A history of Mars
by Greg M. Orme.
Mars has a mysterious history. Many of the facts we know seem to be conflicting, for example it seems to have had a history of water flows which seems to contradict its current cold state. Valles Marineris is also hard to explain, a large rift valley with apparently no plates, which are needed on Earth to create them. There are many water flows from craters but there should be no water in those areas. Craters are unevenly distributed on Mars, covering only half the planet to a large degree and this coincides with a drop in height called the dichotomy boundary.
Here an attempted explanation is made based on large scale events, which may have driven most of the Martian changes and created the paradoxes we see today. It is a forced sequence of events so if the basic premises are accurate then it is quite likely something like this occurred, though perhaps in a different order.
The 4 largest outside influences we know about Mars are probably the last four big impact craters, Utopia, Isidis, Argyre, and Hellas. Since much of the confusion about Mars arises from the fact that we don’t perceive its evolution to be understandable compared to our own, this theory attempts to explain it by outside events driving the changes.
If a planet was perfectly round a pole might tend to wander over time. Usually planets are a spheroid, which means they are like a slightly flattened ball, and the wider parts tend to be at the equator. This is because the extra weight tends to go to the equator where it wields more force because it spins faster there.
The converse of this is that an absence of mass such as an impact crater or large valley like Valles Marineris would tend to go toward a pole since they become the equivalent of the flattened part of a spheroid. We also know that on Mars large impacts typically form a Mons or mountain on the other side of the planet, though sometimes not exactly opposite the crater. Logically this Mons would take a long time to form and we know that the Tharsis Montes for example probably continued to grow and restart through much of Martian history.
So at first with an impact there is an immediate tendency for the crater to move to the pole, and then as the Mons grows on the other side this weight fights to move to the equator and eventually may overcome the lack of mass in the crater. Also the crater may partially fill up over time as Utopia Basin appears to have. It may then be that at first the crater moves to the pole and then after time moves toward the equator as the Mons grows. By having 4 impact craters and their associated Mons doing this it can make the resultant climate on Mars vary wildly, and make it much harder to decipher.
Also as a crater moves toward a pole its gravitational influence diminishes, so it will likely stop near but not exactly on the centre of the pole. It may also fill partially with ice and this addition of mass in it can further stop it moving closer to the pole. If the climate then changes for example with the heat added to the atmosphere by the volcanism of the Mons then this amount of ice can further fluctuate moving the pole as well. This would be because the warmer climate might move ice from the pole to the equatorial regions, and perhaps sublimate CO2 from the poles.
While a Mons can be initiated by an impact it can also be altered or even restarted by additional impacts if the shock waves are strong enough. For example in here I will show that Isidis may have weakened the Tharsis area, which was further affected by an oblique impact from Argyre, and then from Hellas. This would have contributed to these volcanoes restarting many times until they reached their enormous size.
Generally it is believed that a large impact like Hellas would naturally make a large Mons on the other side of Mars, but the record from large impacts is not so clear. Utopia Basin and Isidis Basin have no large Mons opposite them, Argyre has Elysium Mons, and Hellas is hard to line up with the Tharsis Montes and Olympus Mons though it lines up well with Alba Patera. There is however enough of a correlation to think they are related.
The main theory is that when the impact occurs the core acts like a lens focussing the shock waves onto the crust on the other side of the planet, either exactly opposite or somewhat offset if the impact is oblique. This theory has several problems however. One is that a spherical core is not really the right shape to focus shock waves like this; such a shape should tend to defocus the waves. Also we don’t know the relative densities of the materials involved so we can’t say for sure what angle of deflections would be made by such a lens. As Mars became progressively deformed impacts happened from different elevations and so it would seem unlikely all of these would just happen to give such a precise focus to create a Mons.
The effect of shaping sound waves by a lens is well known, dolphins use it for example to direct their sonar.
A more likely explanation might be that as the shock wave spreads there is a small cone of the wave that goes directly through the centre of the core and other layers, and because over this area the surface of the core is relatively flat then this cone of the shock wave would tend to be not defocused. Outside of this cone the shock waves would tend to be defocused and perhaps distributed evenly over the opposite hemisphere to the impact crater.
People who need glasses can see a similar process. Squinting can improve eyesight because the light goes through a narrow aperture, which is similar to shock waves going through the centre of the core. The narrow beam that gets through the core without being defocused might by itself create only a very narrow circle of damage on the surface crating one small volcano, compared to a large area of devastation.
Other parts of the shock wave may even be reflected back so we may get bands of general volcanism as the force is distributed over a large area. For example the core and other layers should have an angle of reflection so that waves hitting at a shallow angle tend to bounce off it and waves at a steeper angle tend to refract into the core. Large enough impacts may even affect the magnetic field in the core and perhaps and stop the magnetic dynamo.
This general spreading of the shock waves could have induced a general increase in volcanism over the whole planet and perhaps in certain bands, so these may explain larger volcanic flows . As we will see later the two main areas of Noachian craters may have been preserved by their having been under poles and thus have resisted volcanic resurfacing.
Some of the Martian names are shown on 2 maps . Also the polar wandering path of Sprenke et al is referred to, these are adjusted to give a polar path more in line with impact craters and known deposits of ice found, which may correspond to old poles. It is not possible to be exact with the positions of poles so long ago; also they may not have been circular. The current poles for example are not, which may be caused by the pole still moving.
The Utopia Impact
While previous impacts may have shaped Mars  I begin here with the Utopia impact basin . Thomson and Head conclude this is an impact basin and also that it is very ancient, likely much older than Isidis, Argyre and Hellas since it is much shallower. Isidis basin is on the edge of Utopia Basin, implying from its shape that it was formed later. There has long been controversy over whether this is an impact basin or an ancient sea. Thomson and Head argue the model of an impact basin as opposed to an ancient sea or ice sheet but the pole in the basin would perhaps make both indicators be seen together. This area could have been a Northern ocean especially when the Utopia impact basin was still warm from the heat of the impact. I refer to the centre of Utopia Basin as North Pole 1 and subsequent poles are in numerical order. The current pole is Pole 5.
Interestingly similar lacustrine and volcanic arguments are made in Valles Marineris which we will see later may have formed from the Isidis and Argyre impacts. If the pole had moved to the area of Valles Marineris in combination with the volcanic activity from the impacts tuyas may have been formed as well.
Smith et al believe Valles Marineris may have formed after Argyre and Hellas, but this may also indicate those impacts helped to increase the rifting after it began with the Isidis impact. Valles Marineris is a large negative gravity anomaly and so should tend to move to a pole as well. With the Isidis impact it was already near a pole, so this tendency was already realised.
As time progresses it moves further from the pole and as we will see towards the equator where it largely remained through further polar wandering. This implies it did not get much larger, or that if it did the negative gravity was compensated by the increased mass nearby of Tharsis Montes, Olympus Mons and the area around Solis Planum. If its rifting had have happened separate from an impact then we should expect to see the advance of the poles towards these impacts to be reversed at some stage when Valles Marineris was formed. This implies then that either it was never a significant negative gravity anomaly which seems unlikely or it formed in circumstances where its lack of mass were already compensated for and this did not change with a widening unrelated to the forming of further Mons from impacts. It is likely then that Valles Marineris was formed around the same time as the Tharsis Montes.
Sprenke et al show no such change in the polar path heading back towards Valles Marineris or even seemingly being affected by it. Smith et al also show how the current gravity of the Valles Marineris area is dominated by Tharsis Montes and Olympus Mons, and also by the area around Solis Planum, which also indicates the Utopia and Isidis impacts could have made that area heavier, slowly negating the negative mass of the Utopia and Isidis impact basins and allowing the pole to move on and this area to move towards its equator at the time. This area is shown in Figure 1.
Isidis Basin also has rootless cones, which according to Martel may be formed by lava flows over water or ice. This would also be consistent with a pole here, and avoids the need to assume large amounts of ice all over Mars. Moore et al believe fluvial erosion occurred in the Noachian to Hesperian.
The centre of this basin is 45 degrees North 248 degrees west, so directly opposite this is 45 degrees south and 68 degrees west. This is shown as A in Figure 2.
Interestingly this area has no Mons at all, though normally there should be one or more from the shock waves. The ground is raised around Solis Planum however and all the way to the Tharsis Montes. It may be then that the rifts around Solis and Syria Planum may have been partially formed from the Utopia Impact, where the whole area was raised rather than a narrow Mons.
The Argyre impact basin is very close to South Pole 1, and it may be that this hit the Mons opposite Utopia Basin, and removed all traces of it. The other possibility is that the Mons was in the area of Syria Planum and was either damaged in the Argyre impact or had eroded to a smaller size. This might account for the generally raised area around Solis and Syria Planum.
The Isidis Impact
The next oldest impact may have been Isidis. If it has happened before the Utopia impact then likely it would show the effects and perhaps have been buried. It seems apparent that water flowed from the Isidis Basin into the Utopia Basin . Argyre also appears to be much younger.
When the impact occurred it would have moved closer to the pole, and the pole opposite would have also moved. The centre of the Isidis Basin is 12.7N 272.6W, giving the other pole as near 12.7S 92.6W, shown as B in Figure 2. This would place it in Sinai Planum. So from one impact to another the pole may have moved from 45S 68W from the Utopia impact to 12.7S 92.6W. We cannot say where exactly South Pole 2 was, though it is likely near a line between A and B.
Isidis is also the landing place for Beagle 2   . Being very flat it is also more likely to be older than Argyre and Hellas. It also has signs of fluvial activity, which could be from when it was at or near a pole. Toon says that large craters and river valleys appear to be the same age. This can be from impacts melting water, but also from impact craters moving to a pole which attracts ice and perhaps water if the craters retain some heat.
The elevated areas between Solis Planum, Icaria Planum, and Aonia then may have been caused by these two impacts. It also turns out that even though water signs were not picked up here by ODYSSEY  the area is thought to contain ancient water deposits  .
Barlow et al suggest the area has contained ice since the Hesperian, which fits in well with an ancient pole having been there. Interestingly they suggest the water table may have tilted here with the formation of Tharsis, which agrees with the time lines suggested in this paper. Instead of or in addition to the water accumulating here from Tharsis it could have accumulated from a pole forming here.
This agrees well with the proposed poles by Sprenke et al, who begin their polar wander at 45S 90W and then move to approximately 30S. It is more difficult to see signs of the opposing North Pole 2 around Utopia Basin though ice signs are seen.
Not only does the area around South Pole 2 in Syria Planum not show ice signs from ODYSSEY but they show the opposite, of being some of the driest parts of Mars. This conflicts with what is seen in Solis Planum, where fluidised ejecta from craters is known. It may be then that there was ice here at one stage but events drove the water out. Since this area is opposite the Utopia and Isidis impact basins it implies that heating from those impacts may have removed the ice. Some ice may still be there.
After the Utopia impact this area would have become saturated with ice and perhaps water as it became a pole, and we know from the ejecta ice was there.
The pole may have extended into Solis and Sinai Planum in the middle of the raised ridges and rifts, though only the ones to the south may have been there then. Since this is opposite the Isidis impact and roughly follows the path of polar wandering by Sprenke and Baker it seems a reasonable possibility.
While the impact of Isidis may explain the lack of water signs opposite Utopia Basin it cannot explain the lack of water signs opposite Isidis itself. An additional event may have happened to make the further rifts around this pole, I call Pole 2 (Pole 1 would have been formed by the Utopia impact). Valles Marineris may have been formed from this further event.
Syria Planum is said by Webb to be surrounded by a raised annulus as well. Stresses then are likely to have created the rifts such as Valles Marineris and allowed these Planum to subside. Instead however of Tharsis forming this strain this may have been done by the combined impacts of Utopia and Isidis, and that forming a pole of ice here restricted the volcanic effects to their perimeter. Scott argues that Syria, Sinai, and Solis Plana were formed with a mantle plume, which is consistent with the idea of heat from the Isidis impact. The subsidence may have been partially formed by the weight of the polar ice. Also Scott says this upwelling may have been enough to form Valles Marineris. This area may also have escaped resurfacing from Tharsis because of this higher elevation according to Smith.
Hartmann says Solis Planum also has well preserved craters, with larger craters more preserved. This may be because of the pole being there for a long time, having buried craters in ice.
Arsia Mons is roughly at 12S 120W, the same latitude as South Pole 2. It is also the largest of the 3 Tharsis Montes as well as being closest to the opposite of the Isidis Impact. Head says evidence of glaciation  has been found also on Pavonis Mons and Ascraeus Mons, which is suggested to be from the late Hesperian. This may also have been from the time the pole was nearby. Few signs of water are seen, which would be consistent with polar ice. Head and Marchant also say that Arsia Mons had volcanic outflows into the Hesperian, which is consistent with later impacts restarting the flows. Sprenke et al say that the Tharsis Montes may have been formed after the Martian global magnetic field ceased, which might imply the Hellas and Isidis impacts had affected this field. It may also mean the volcanoes were reactivated later in subsequent impacts. Vast amounts of ice may be there even today.
Next the Argyre impact may have occurred. Assuming South Pole 2 was at Sinai Planum it would have been likely that this was an oblique impact. Argyre Planitia is shallower from the West to the North though it is deepest to the North West. Argyre is centred on approximately 50S 42W, and the Sinai Planum South Pole 2 may have been at 12.7S 92.6W. Sprenke’s pole position would be 30S 90W so both give an oblique impact assuming the meteor came from within the ecliptic plane of the asteroid belt.
Looking at the higher elevations North West of Argyre Basin it seems these reach from Argyre all the way up to Valles Marineris and west to the northern edge of Icaria Planum, seen in Figure 3. Illustrated in Figure 4 if you draw a line though Olympus Mons A and Pavonis Mons B then Arsia Mons and Ascraeus Mons C would be at close to right angles to this line as would the annulus D to the North West of Bosporos Planum. This also points at the centre of the Argyre Basin. The annulus west of Syria Planum and Solis Planum E would be approximately the same angle as Valles Marineris shown here as two lines F and G.
It may be then that while these features were partially formed by the Utopia and Isidis impacts the glancing blow of Argyre sent a shock wave in a shallow angle and created them. This would be the same mechanism as an impact on the other side of a planet except in this case the main shock wave comes from the side. The shock wave is always strongest in the path of the impact because the sound waves are most compressed along that line by the speed of the meteor and hence the frequency is most raised. So the strongest force in an oblique impact should be along the line of the impact trajectory.
This triangular shape can be approximated by shining a torch onto a circular bowl at an oblique angle, though the sides are more rounded. A shock wave would generally be cone shaped rather than cylindrical like a torch beam but the diffusion is unlikely to be great over this distance. As the beam goes through the pole at a shallow angle it would come out roughly in this triangular shape. The edges of the shock wave would tend to shear the ground creating an approximately triangular or egg shaped annulus and rifts. Rifting and faulting would tend to be in straighter lines making the shape more triangular.
The same thing may have created the triangular shape of Olympus Mons and the three Tharsis Montes, perhaps from a reflection from a subsurface layer. If a shock wave hits a denser layer below at an angle it may glance off like a light beam reflecting off a pane of glass at a shallow angle. The shape of this shock wave can be seen by shining a torch on a globe (representing the denser layer) at an oblique angle.
The shape is approximately the same, and faults would tend to be in straight lines to create the Tharsis Montes in a straight line. Here Tharsis Montes and Olympus Mons are overlaid on this annulus shape together with Valles Marineris to show the similarity of the two shapes.
Another possibility is that the shock wave pointed directly at Tharsis and Olympus Mons, and a reflection made Valles Marineris and the rises. A geological layer would not reflect perfectly because of its rougher surface so some parts of the shock wave would go through and another part would reflect even when the angle of reflection favoured one or the other. A good analogy would be for light reflecting off frosted or roughened glass where some parts would reflect and others refract.
In this case then Valles Marineris would have been stressed but not rifted by the Isidis impact and upwelling and then sheared into a rift valley from the Argyre shock wave.
There are no signs of volcanic activity in any other direction from Argyre, which also implies a glancing impact. On the other side of Mars Elysium Mons would have been also formed from the impact. There are three Mons opposite Argyre, Hecates Tholus, Elysium Mons, and Albor Tholus. This also connects the shape of Tharsis Montes plus Olympus Mons to the three opposite Argyre. The triangular shape of these three Mons may have occurred from a refraction of the somewhat triangular shock wave.
Hiesinger has out six scenarios for the evolution of the Argyre basin. Surious Valles has a delta shape, which may have been from water as South Pole 2 melted. There is also evidence for a proglacial lake. Water signs are found there but too high for water to come in from the northern lowlands. A polar meltback was proposed by Parker et al though not in the South Pole 2 position.
Elysium Mons is close to the Isidis basin which would have been the opposite North Pole 2 at the time.
Such an oblique impact hitting the polar ice may have expelled large amounts of water and ice from Mars; indeed it is hard to imagine an event more likely to do so. Also if at this stage Mars had substantial amounts of frozen gases such as CO2 at the pole this could also have been ejected leaving the atmosphere much thinner. Much material from the crater may have also been removed from mars which could have subsequently made its negative mass more influential relative to the coming shift to Pole 3. Some ejecta may have added to the annulus to the west of Bosporos Planum D and even to the raised area further North West.
The subsequent heat would have melted much of the pole and raised the overall Martian temperature. If gases were frozen this would have raised the air pressure and allowed more liquid water, also floods from the ice melting were likely. Signs of these are probably shown in Valles Marineris which has an elevation sufficient to carry water into Margaritifer Terra and Chryse Planitia which are also shown in Figure 4. In Lunae Planum there is also evidence of large scale flooding, also on Xanthe Terra, but little south of Solis Planum and perhaps some into Argyre Basin which would be too hot at this time for water to channel into it. The water may also have gone North West if Tharsis was not large at this time.
South Pole 2 would try to reform polar ice and water but the heat would drive it away. This then may explain why this area had evidence of water from ejecta in craters but this seems to have disappeared according to Odyssey, also shown in Figure 5. As shown in Figure 6 one red section appears to radiate out of Argyre from the west A to the north B, and the second one sits in Solis Planum C where South Pole 2 may have been. This indicates the Argyre impact may have dried out these areas, which is why they showed fluidised ejecta in the past but now show little ice. It may even have dried out east of Ascraeus Mons.
Later water would drain from the Argyre Basin as it cooled and water ran into it from South Pole 2. The raised annulus west of Bosporos Planum may also have prevented water going to the basin, as well as south to Aonia.
Thaumasia shows deformational features radiating from the Argyre Basin which may show the impact had influence this far. While also radial to Tharsis here they may be more related to Argyre.
The large negative mass of the Argyre basin would have begun a pole shift. Also as the impact helped to grow Tharsis Montes and Olympus Mons they would have tended to move to an equator which would have also helped to shift the pole. As we will see according to the polar wander path of Sprenke and Baker Tharsis and Olympus Mons move directly closer to an equator westward, which in turn moves the pole eastward.
Sprenke et al show a movement of the pole to approximately 0S and 30W and then to 330W. This would take the pole to North of Argyre Basin into Margaritifer Terra and then east to Meridiani Planum. Since it is unlikely the pole stopped in Margaritifer Sinus this is not given the name South Pole 3, that is for when the effects of the Argyre impact stabilise a new pole. So the pole wanders from Sinai Planum A through Margaritifer Sinus B to Meridiani Terra C heading eastward, shown in Figure 7.
According to Grant Margaritifer Sinus contains high valley densities, which would be consistent with the pole moving and subsequently ice melting. Also the area was resurfaced several times, perhaps from the subsequent volcanism from the Argyre impact. While Grant believes some precipitation occurred most would have been from ground water, which is consistent to a water table associated with a forming pole. This discharge lasted a long time according to Grant. The Parana Valles drainage system is particularly extensive.
Hynek et al believe this time of fluvial resurfacing lasted several hundred million years. A combination of rainfall and sapping appear likely, which may have formed a lake for a time. A moving pole then may link the two main theories of precipitation and sapping to explain the valley networks, and that according to Nelson a large build up of ice which periodically melted. Philips et al examined Margaritifer Sinus and concluded much of the Tharsis bulge was already in place before the drainage channels were formed, which is consistent with the general rise in elevation in the area of Tharsis and Sinai Planum from the Isidis impact. Further growth of Tharsis could happen later, though at the late Noachian it was large enough to direct the channels northward. Large amounts of material from this area were removed along these channels probably from water erosion as the pole melted, and moved into Margaritifer Sinus.
Valles Marineris   is then likely to have formed from the stresses of the Isidis and then the Argyre impacts, making its origin harder to see . By this time water and ice would have accumulated in it as the pole melted and moved, which may explain the paleolakes. Carr suggested that ground water flowed into Valles Marineris and then into Chryse Planitia, forming lakes. Rossi et al believe there is good evidence of ice and glaciers which would be consistent with a polar area.
Lunae Planum, also shown in Figure 7 would also have received water from the moving and melting pole. Greeley and Kuzmin show how Shalbatana Valles originates in the chaos on Lunae Planum. Interestingly it comes from a probable impact basin that formed a catastrophic outflow. This impact may have occurred before or at the same time as Argyre, though its shape (not mentioned by the authors) would likely be elliptical if from the time of South Pole 2. While it is suggested the impact breached an aquifer this would be unusual for Mars. It does link the area with large amounts of water and probably ice triggered from an impact, something not seen elsewhere. A pole here would supply the water, and once it carved a channel keep it going with more water. A nearby elliptical formation, Orcus Patera may also have come from an impact, its shape implying a pole was near here.
Xanthe Terra also shows evidence of water flows. Nelson and Greeley discuss 3 major fluvial events here. The first is a broad sheetwash from the Valles Marineris area perhaps coinciding with the Argyre impact. Then there was more extensive water forming Shalbatana, Ravi Simud, Tiu, and Areas Valles which might coincide with the pole moving to Margaritifer Sinus. Most of this water came from chaos areas which would link to the Argyre impact. Subsequent flooding would be as the pole continued to move, and when further enough away the water would cease.
In the new Odyssey results of subsurface ice there is a large deposit on the equator in Babaea Terra shown in Figure 8 and centred at 330 degrees west. Another one can be seen on the left edge of the map just below the equator shown in Figure 9. This would correspond to the opposite pole. According to Sprenke et al the pole moves in a curve through this ice rich area to 0S 330W, almost the centre of the ice rich area. I call this area South Pole 3. Having icy areas opposite each other like this makes it likely they were poles.
This can be explained from the effects of the Argyre impact. As the Tharsis and Olympus Montes grow they accumulate more mass which seeks to go to the equator. The movement of the pole to this area allows these to get much closer to the equator. Tharsis and Olympus Montes are today on the equator at around 120W and the pole would have moved to 330W. This adds to 150 degrees so the Montes would have nearly reached the equator, which indicates their weight was dominating at this stage. The pole has assumed a position between the Argyre and Isidis impact basins as each would have had a tendency to be near the pole.
This would tend to be a stable configuration. The Montes have grown enough to get near the equator so little more can move them closer. Elysium Mons has probably also formed to some degree which reduces some of the negative mass tendency of the Argyre Basin. It is at 210W so there is more than 120 degrees between there and the pole. Pole 3 then would be balanced with Olympus Mons and Tharsis Montes tending to go to the equator and Elysium Mons almost opposite them also near the equator, and Isidis, Utopia, and Argyre basins around South Pole 3.
This also implies the growth of these Montes is strongly linked to the Argyre impact as the pole moved from near the Argyre Basin to mid way between it and the Isidis basin. If the Argyre impact had not happened then, its happening now would scarcely move the pole. It would be unlikely an impact causing the Argyre basin happened then just at a time where it wouldn’t move the pole. Also that Elysium Mons has moved towards an equator which it wouldn’t have done if it hadn’t formed yet. Logically then the Utopia, Isidis, and Argyre impacts had to happen in this order, forming their respective Mons in the order described for this polar wander path suggested by Sprenke.
Interestingly South Pole 3 coincides with an area of heavy cratering and the second cratered area corresponds well with the opposite North Pole 3 in Figure 9. One likely explanation is that the polar ice protected the craters from erosion, and when they were exhumed from the ice they remained in more pristine condition. Pole 3 probably lasted a long time to give this crater disparity. It also implies at this time that the surface was being altered severely and other craters were being buried or obliterated by lava flows.
This may be because of the shock wave effect of these impacts which may have sent shock waves over large parts of the surface initiating volcanism. This would explain how volcanoes have apparently restarted in Martian history and the surface being relatively young in parts. Pole 3 likely remained here through this resurfacing. Since these crater areas are linked into what is termed the Noachian surface it may be that the time after the Argyre impact may be regarded as the Hesperian, obliterating much of the Noachian terrain except for these parts protected with polar ice. Some other areas with Noachian craters are also found around Margaritifer Sinus, implying the pole may have slowly moved and protected other areas for a time in its path.
In moving from Pole 2 to Pole 3, the polar ice closely follows and may have formed the dichotomy boundary. The main boundary is seen between 180 degrees west and 90 degrees west, which is 270 degrees or ¾ of a total possible boundary. The rest is taken up by the land mass of Tharsis Montes, Syria Planum, etc. South Pole 2 moved from 12.7S 92.6W eastward to approximately 0S 330W, which is approximately 122 degrees of longitudinal movement or approximately 1/3 of the total great circle. The opposite pole travels from 12.7N 272.6W to 0S 150W, which is where the dichotomy boundary ends against Olympus Mons, for a movement of 122 degrees. This makes then 244 degrees of movement over a dichotomy boundary of 270 degrees as a polar path. The rest can be explained by the width of South Pole 3 at 330W, which makes it appear to extend further east. So of the total visible dichotomy boundary virtually all of it is on the same line as the movement of Pole 2 to Pole 3 which is unlikely to be a coincidence.
The pole then moves through Margaritifer Sinus and from here there is a green elevation path. This trail begins at east south east of Pole 2 so the pole may have initially moved towards the Argyre crater, which is logical as its negative mass should move towards the pole. This implies the pole may have moved along this green area and lowered the terrain there.
The pole was probably moving on a slope, which may make the path easier to see than from South Pole 3 to South Pole 4 where the ground was not sloping. We already know the planet tends to slope towards the current North Pole, North Pole 5, and that this polar path is lower than the terrain south of it, and higher than the terrain north of it. This then implies the moving pole may have flattened part of a slope going into Acidalia Planitia and for the opposite Pole Elysium Planitia.
A pole moving on a slope like this would tend to have a runoff of water heading North through the journey. Depending on the temperatures and the air pressure at the time ice may have sublimated directly into water vapour and CO2 may also have been a primary erosional force. On the sloping ground water, mud and perhaps CO2 ice would tend to move like glaciers, with material in the ice moved north through avalanches and liquid CO2 as described by Hoffman. Dust that formed on the pole through dust storms then would be moved north and perhaps create a very smooth surface in Acidalia Planitia, Utopia Basin and Elysium Planitia.
As the pole moved new ice would tend to form on the ground ahead and melt on the ground behind it as the temperatures changed. The ice in front would tend to freeze into the soil and create a similar situation to the current Pole 5 where approximately half or more of the soil is ice. When this eventually melted or sublimated the soil in the ice should have moved down the slope and spread out. If there was a high enough air pressure this should have created a seasonal water flow into Acidalia Planitia and created the smooth surface. CO2 might give the same movement at lower temperatures.
It is likely the temperatures of Mars were dropping from the Argyre impact, there are visible water channels in Lunae Planum, Xanthe Terra, and Margaritifer Sinus, but these are no longer seen as the pole moves eastwards. The edges of the green elevation may indicate the edges of the permanent ice cap.
This may mean then that the primary erosion was from ice and CO2. Some channels are found north of South Pole 3 in Arabia Terra, but these may be from the Hellas impact later when the pole moves again. If so then this would again imply the temperatures and air pressure were too low after Margaritifer Sinus for water erosion. More investigation of this polar route should confirm whether channels existed.
The ice deposit at South Pole 3 abuts a cliff to the north, which is an extension of the dichotomy boundary. This ice then implies that it is connected to the creation of this cliff and by extension created the cliff of the dichotomy boundary as the pole moved. As water ran down the slope at South Pole 3 it would have eroded the ground, but where the ground was permanently frozen the ground would have been protected. This should then give a boundary to the north of the moving pole where the ground slopes more.
The speed of the polar wander should be according to how quickly the Tharsis Montes and Olympus Mons grew, with their tendency to go to the equator. Also as the pole moved away from Argyre it may have been held back because the negative mass of the Argyre impact basin would tend to be near the pole. As it came closer to the Utopia and Isidis impact basins it may have accelerated, releasing more water. These basins would counteract to some degree the negative mass of Argyre as they too would seek to be near a pole. It may also be that with the polar movement the channels would be regularly changing and so did not form as large as in Margaritifer Sinus.
The Hellas Impact
The Hellas basin is centred at approximately 40S and 290 W. This would have made it about 40 degrees from South Pole 3 and so would have been an oblique impact, though not as much as Argyre. Almost exactly opposite Hellas is Alba Patera, again probably formed from the shock waves. The resultant shock waves may again have gone around Mars stimulating volcanism, perhaps restarting Tharsis Montes and Olympus Mons which are also close to opposite Hellas. It may also have stopped Mars’ magnetic field. Sprenke and Baker point out that the rotational poles closely follow the movement of Pole 2 to Pole 3, but this does not appear to extend to Pole 4. This may be because the Hellas impact stopped the magnetic dynamo with the shock waves.
Anderson et al analysed Syria Planum in comparison to Alba Patera. They concluded Syria Planum is Noachian to late Hesperian with intense activity that declined later. This would be consistent with its initial formation from the Isidis impact and later from the Argyre impact. They consider Alba Patera to be similar, which is plausible if it was formed by the Hellas impact. This is considered to be extending from the early Hesperian into the Amazonian and so is later than the Syria Planum volcanism. They believe that Syria Planum had a greater impact on Tharsis than Alba Patera which is again consistent with the impact sequence.
The large negative mass of Hellas would have tended to move the pole towards it, and Sprenke found from elliptical craters that the pole probably moved to 45S 345W. This places it on the edge of the Hellas Basin in the direction of the Argyre Basin, probably with the two negative mass craters tending to both be near the pole. This is the same as in South Pole 3 where Argyre and Isidis basins were both near the pole. It is closer to Hellas probably because Hellas is much larger than the Argyre Basin, being younger. There are many large craters in this area as well; some may also have been preserved through burial under the polar ice. I call this South Pole 4.
In Figure 10 A is South Pole 3 and B is South Pole 4. This is now relatively close to Pole 1 at 45S 68W. There is approximately 83 degrees of longitude between Pole 1 and Pole 4, and they are on the same latitude.
Also in this pole position Isidis is on the equator which means that Pole 2, Sinai Planum, and Tharsis Montes are also now on the equator. The pole then has moved to near Hellas while maintaining much of the weight of the Mons on the equator. This is consistent with the weight of Olympus Mons and Tharsis remaining on the equator, and the pole moving to the negative masses of impact craters.
Hellas is an oval shape approximately twice as long as it is wide, probably from the oblique impact. Since Hellas is approximately 45 degrees from South Pole 3 this would imply an impact at 45N at the time, and the oval shape indicates an impact on the western side to give the oblique angle pointing mainly at right angles to South Pole 3. This is likely as to the west of Hellas there is a reddish area with much less ice, shown in Figure 11. The icy area of South Pole 3 is elongated pointing along the path of the polar wander to South Pole 4. The section west of Hellas basin much drier is shown as from C to D. Since this is in a direct line with the longest part of Hellas it is likely this was formed from ejecta or shock waves making this area hotter for a long time, and eventually drying the area when South Pole 4 moved. This is the same mechanism as might have happened with the Argyre impact drying west and north of it in Figure 6.
The icy blue area of the current South Pole reaches to Hellas and implies the pole may have wandered east into Hellas and then south to the current position, as shown in Figure 13. The lack of ice on South Pole 3 may also indicate the climate was warmer from the heat of the impact and stopped large amounts of ice forming.
The corresponding North Pole would then have moved to the east of Alba Patera in Tempe Terra. There is a possible platform there similar to that south west of Alba Patera. The pole may have moved as the gravitational influence of Argyre lessened, with the basin filling up and Elysium Mons growing larger. This would move South Pole 4 to the east away from Argyre, there may be another platform on the eastern side of Hellas Basin. This would also be consistent with water gullies, which in other parts of Mars are near former poles. If the pole moved to eastern Hellas Basin this would explain gullies in Dao Vallis and Tempe Terra. It may also be that the polar ice extended eastward to there.
This would also be consistent with the shape of the current poles. Chasma Australe points to 270W and may have been formed by water melting as the pole moved, the pole perhaps still moving. Promethei Planum would also have been formed from the pole moving away from South Pole 4. A hot spot creating basal melting may have formed Chasma Australe but the moving pole could have also supplied the heat, the leading edge becoming colder, and the trailing edge warmer.
Hellas seems to have contained ice covered lakes which would be consistent with being near a pole. It can be seen that the moving pole may have made a lot of different areas appear to be ice rich and often to have fluvial flows, even glaciers and hydro volcanism. This could solve the mystery of why Mars has so many water signs and apparently not enough ice available to cover them all. It also can explain that even though the temperature has likely been too low for liquid water, channels are widely seen. The moving pole would have moved water and ice with it affecting each area in turn, looking as if there should be perhaps 10 times as much water on Mars.
Chemically Mars resembles a dry planet so outside of these poles there may have been little ice or water, and CO2 erosion may even have predominated at times. Each impact would have temporarily heated up the planet giving perhaps brief times of liquid water and perhaps higher air pressure through sublimated gases.
The various Mons might have been periodically restarted from shock waves from the impacts and the resulting heat kept the planet warmer for a time, until eventually all volcanic activity ceased and Mars reverted to the cold planet we see today.
Thomson and Head believe glacial features, moraines, drumlins, and eskers are to be found in Hellas, consistent with being near a pole. According to them this could have been part of an ice sheet and a proglacial lake, possibly middle Amazonian. The lake they believe would have held enormous amounts of water that has disappeared, consistent with water from a pole that moved on.
Jakupova et al have laid out a distribution of craters 10 km and over. This boundary of heavy cratering closely follows the movement from Pole 2 to Pole 3 and indicates when the resurfacing of the north may have occurred at this time.
This is consistent with the poles moving water and sediments northwards, and burying craters. There is an area above Margaritifer Sinus which is nearly devoid of craters; this is likely to have been resurfaced in the floodwaters in the movement of South Pole 2 to South Pole 3. Isidis is comparatively devoid of craters, and this continues in a line with the movement of North Pole 2 to North Pole 3. This would again be from transporting sediments and water north and removing craters. The area north of the equator and 60 degrees west extends high into the northern hemisphere with heavy cratering. This area was found by Odyssey to be drier and indicates that a lack of water is associated in this area with cratering.
Layers are Mars are thought to have been formed by dust alternating with CO2 or water ice. As water and ice were moved north by the movement of Pole 2 to Pole 3 it would have deposited on these layers. With this pressure and with liquid water the tendency would be for the CO2 and ice to melt and move upwards, which would make the layers collapse and the ground to lower in elevation. The movement of water northwards then could have created a lowering of the ground forming the Northern lowlands. This lowering in turn would enable a large sea, ice sheet or mud ocean to form and the collapsing of layers to become more and more widespread. If so then the southern hemisphere may have substantial amounts of CO2 and ice still trapped in layers.
The northern hemisphere is seen as Amazonian and the Southern surface as Hesperian implying the southern hemisphere is older. This is however from crater counts and it is possible that the craters in the northern hemisphere may have been removed and buried in this process.
After the Argyre impact the formation of the volcanoes may have added a lot of ash into the atmosphere which would have tended to collect at the cold trap in the poles. This would have subsequently been moved northwards as the poles moved.
Permanent ice in the north would tend to compress the ground leading to polygons when the ice was eventually removed. Dust and accretion from meteors would have built up on the northern ice as well as in the south. As meteors impacted in the north they would have fallen on ice and so not left a permanent mark. Head et al show that the northern lowlands contain areas of polygons, craters with ejecta lobes, and potential coastlines.
Deviations in the Contact 2 coastline may be accounted for by changes in Tharsis and Elysium Mons which would be occurring as the pole moved, and later.
When eventually the planet became colder after the effects of Hellas and Tharsis wore off the air would have begun to freeze and go to the poles. Then the northern ice would also have sublimated, some may even still be buried as a frozen ocean. The material that had built up on the northern ice would have fallen down onto the craters that had been preserved under the ice, and buried some of them. This material would appear similar to that of the south, and likely not show signs of water as it came from the surface above the ice. Some of the northern ice sheet may have been liquid underneath around Tharsis Montes, Olympus Mons, Alba Patera and Elysium Mons because of their heat.
Some of these surfaces then may be smooth from having been sediments on an ocean floor in this way. Others areas may be smooth because as the ice sublimated the material fell smoothly.
Amazonis Planitia is thought to be flat from sedimentation or fluvial processes according to Head. This is north of where North Pole 3 stopped. Also the outflow channels may be partially from when South Pole 2 in Syria Planum melted and began moving. Arsia Mons which is the most southern of the three Tharsis Mons may have been much smaller then. Some channels leading to Amazonis Planitia point north but to the east some point more to the North West.
Lucas Planum is described by Cabrol et al as an estuarine delta. If so then this may imply that the movement of Pole 2 to Pole 3 was accompanied by water flows as the pole melted. It may also have formed water locally from the heat of Apollinaris Patera, or from when the pole began to move north towards the future site of Alba Patera after the Hellas impact. Alba Patera has steep sides and may have formed in the polar ice of North Pole 4. Fuller et al believe this area was resurfaced volcanically and with fluvial sediments. This could be for example from when the Hellas impact restarted some volcanism in Olympus Mons and started melting and moving Pole 3.
The Medusa Fossae Formation follows the path of Pole 2 to Pole 3, and has formations similar to a pole according to Fuller et al.
McGill refers to the younger material sitting on the older Noachian material, which is consistent with the dust layer settling. The buried materials are similar in age to the southern highland, which is consistent with the idea that this was buried under ice and then overlain with dust as the ice sublimated. In this case the air pressure would already be low so there would not be a liquid phase, hence no water to leave signs of the removal of the ice and chemical signs of water having been there.
Watters shows lobate scarps are found south of the dichotomy boundary suggesting that compressional deformation was involved in the boundary’s formation, which is consistent with the weight of polar ice. While he suggests that this occurred in the early Hesperian Anderson et al believe Alba Patera was also formed in the early Hesperian to Amazonian, but the impact of Hellas may have defined the start of the Amazonian from the Hesperian. Since the Noachian, Hesperian, and Amazonian are calculated from crater records the impact of Hellas here may have changed these same crater records of the Hesperian to Amazonian at least around Alba Patera.
Head et al believe much of the northern lowlands were resurfaced volcanically and in some areas as sublimation residue from frozen ponded bodies of water. This may have occurred by the diffusion of shock waves from the Hellas impact over the northern hemisphere of Pole 4.
Tanaka et al believe the northern lowlands were smoothed by glaciation. This would be consistent along the dichotomy boundary while it was forming, if there was a larger icy area north of the moving pole that was melting and reforming. If the air pressure was too low then this could have been from ice sublimating.
Hoffman et al believe flood channels from Cerberus Rupes may be from CO2. This area is to the north as the pole moved southwards from North Pole 2 in Isidis Basin to the North Pole 3 position. This then may give CO2 through this area, in combination with flood water from the melting pole. The actual flooding depends on the temperatures but this area is equivalent to Margaritifer Sinus. South Pole 2 had begun moving and released water into Lunae Planum, Xanthe Terra, and Margaritifer Sinus, so the opposite pole would likely be releasing water at the same time as it moved.
Since CO2 typically sublimates on the current poles in summer this same mechanism would presumably be operating as the pole passed this area. It is not known at this stage whether CO2 can account for these effects, but it is likely that it was available.
Burr et al believe flood water originates to the north of the Elysium Basin and Marte Vallis. A lake in Marte Vallis may have been fed from Medusae Fossae to the south. Ice from the pole moving to the North Pole 3 position may have been heated by Elysium Mons which would be forming from the Argyre impact, and so may have provided heat to the area. They also conclude precipitation was unlikely to form the channels because nearby areas show no erosion from rain. Groundwater is likely to form from a nearby pole, and the heat from Elysium Mons should turn this to water when the pole got close to the area.
Burr et al see rootless cones though Athabasca Valles, which can from lava on wet ground. This can be from the volcanic activity from the Elysium Mons area caused by the Argyre impact, and water from the passing pole. The carrying of sediments is consistent with the idea the moving pole may have carved out the dichotomy boundary, and floods moving the sediment north. Ice from north of Elysium Mons may also have been melted by volcanism giving flood water.
While the pole was here each summer, water or ice may have fallen down the slope of the dichotomy boundary off the northern edge of the pole, and the dichotomy boundary here could have been the edge of the permanent polar cap. The edge would form here because each summer water or perhaps ice or CO2 avalanches would fall down the slope, eroding it away till it abutted the permanently frozen cap. In figure 17 at A an ice trail, possibly from this water connects to higher ice areas. With higher ground to the south water may have tended to go north.
As the pole moved from North Pole 3 to North Pole 4 it moves close to Olympus Mons and the Tharsis Montes, which may have restarted from the shock waves of the Hellas impact. If so then the movement of the pole near such hot areas should sublimate frozen CO2, so this time was probably one of higher air pressure. As Alba Patera formed from the Hellas impact at Pole 4 the heat would also have kept CO2 from freezing there and raised the air pressure. Since this would keep one pole from having as much frozen CO2 the overall air pressure should have been substantially higher for a long time.
This places the North Pole 4 just to the north and North West of Olympus Mons shown in Figure 19. Milkovith et al interpret this area to the North West of Olympus Mons to be glacial, but much large than terrestrial glaciers. This would be consistent with polar ice. Each of the Tharsis Montes according to Head also shows glacial signs, perhaps from as the pole was passing. Since a pole should slow as it nears its resting point there may have been a pole on the Western edge of the Tharsis Montes for some time.
This is the current Martian pole. As time progressed Alba Patera became larger, perhaps cancelling out the negative mass of the Hellas basin. The current poles have the major Mons all near the equator just as they did at Pole 3 and Pole 4. This indicates that from the time of Pole 3 the polar wander had to move so as to keep these large masses on the equator. Since Pole 3, 4, and 5 are roughly in a straight line this would have been controlled by the Mons and indicates they are older than these three pole positions.
Pavonis Mons is on the equator and Arsia Mons the largest is at 10 degrees south. Olympus Mons is at 20 degrees North and Ascraeus Mons at 12 degrees north. Elysium Mons is at 25 degrees north.
Once the ice in the northern hemisphere started to sublimated and move to the poles this would have created a large negative mass that would have acted like a crater. The pole would have tended to move to the gravitational centre of this which would move it from Hellas Basin to the current position. Since most of the ice came from the north this may explain why  the North Pole 5 has more ice.
Since the shift to Pole 5 temperatures may not have allowed this additional ice to sublimate and equalise the amount at both poles.
Chasma Boreale on the North Pole 5 points to approximately the North Pole 4, and Chasma Australe on South Pole 5 points approximately to South Pole 4. Both of these are the largest chasma on their respective poles. The poles may even still be moving which would explain why the South Pole is asymmetrical.
The North Pole seems similarly asymmetrical . Both shapes seem to elongate at right angles to the previous pole positions. This would follow as the pole moved the forward edge would represent a line of temperature low enough to form a permanent CO2 cap. Clearly the elongation could not point into the movement of the pole as this would be against the temperature gradient.
Byrne et al found evidence of short term change on the current Martian South Pole, in the “Swiss cheese” formations. This is consistent with the idea that Pole 5 is still moving, though it seems unlikely such short term changes would be associated with the pole moving. Changes may occur in spurts as areas collapse with the changed temperatures. One analogy might be the changes in glaciers on the Earth’s pole which can change suddenly from the slower global warming.
These structures are found on the forward edge of South Pole 5, and the spider formations are found directly opposite this on the other side of the pole. It may be then that these “Swiss Cheese” formations may be older spider areas that have slowly been moved into colder areas and are now permanently frozen. In this way the similarity between the Swiss Cheese shapes and the spider bushes can be explained.
Some of the spider formations would then be left behind as the pole moved on its trailing edge, and we see this as spiders that merge into apparently inactive areas there.
Pathare et al believe recent changes in the Polar Layered Deposits may have been caused by changing obliquity though these could also have been caused by the moving pole. Layering is seen along the path of Pole 2 to Pole 3; implying layers may be formed as a pole moves.
Malin Space Science Systems recently reported in Science more examples of changes on the South Pole. Hoffman shows gullies on the current South Pole may be undergoing changes, again consistent with a moving pole. These pitted areas however are also significant in relation to South Pole 4, and the gullies may have been formed at that time. M1003736 mentioned by Hoffman is at 70.91S 358.7W, which is closest to South Pole 4. This would explain their pristine condition if they were moved into the polar area after the pole shift from Pole 4 to Pole 5.
The Ages of Mars
The three ages of Mars, Noachian, Hesperian, and Amazonian are primarily based on craters counts. If the polar wander theory is correct then these time scales will be distorted by resurfacing after each of the four major impacts. The Argyre impact may have been so influential it might be said to have begun the Hesperian, forming Valles Marineris, Olympus Mons, the Tharsis Montes, the dichotomy boundary and Elysium Mons.
As an alternative guide the four impacts might themselves be defined as the start of an age. There would then be the ages of Utopia, Isidis, Argyre, and Hellas. This can be much easier to work out the ages of various formations as the beginning and end of each age is a fixed date. Ages could also be defined according to volcanoes, e.g. the Age of Tharsis, Olympus, Elysium, and Alba Patera.
An approximate age can be determined for each impact, and then a tree of cause and effect can be created following on from each impact. Then the age of each event that follows from an impact is determined and added to the tree. This in turn enables the age of each impact to be more precisely determined. Other events that were sufficiently independent could be portrayed as separate trees of cause and effect.
The age of Utopia may have begun to form some of the area around Solis and Bosporos Plana. There may also be areas to the north west of Elysium Mons that could be dated according to this impact. It may have formed a Mons that was destroyed by the Argyre impact, if so then signs around the Argyre Basin may be dated according to Utopia as a benchmark.
Many of the effects of each impact would happen relatively soon afterwards and there would be a long time between impacts dates. Many formations should then be able to be connected with an impact and more accurately determined. This is especially useful where each impact changes an area in turn. For example the area around Tharsis Montes may have been altered by all four impacts.
The age of Isidis could be initially estimated by comparing the relative age of the Isidis and utopia Basins. This in turn may date some of the changes to the Solis, Syria, and Sinai Plana, and perhaps earlier changes to the future Tharsis and Valles Marineris. Geologically it is easier to calculate the ages of these formations by showing how craters counts are changed by resurfacing.
The age of Argyre may have formed the Tharsis Montes and Olympus Mons. If so then craters on them may help date Argyre Basin. The beginnings of Valles Marineris, Candor, and Ophir Chasma could be dated to shortly after the Argyre impact. After this the water channels of Lunae Planum, Xanthe Terra and Margaritifer Terra could be estimated.
In turn this can be compared against the age of the dichotomy boundary which would be formed later. This may in turn allow the time of the formation of the northern lowlands to be determined, if much was formed after the Argyre impact.
The age of Hellas would move the pole from Lucus Planum northwards and begin the formation of Alba Patera. This may also date the restarting of Olympus Mons and Tharsis Montes from the shock waves of the impact. The combined heat from these volcanoes may have resurfaced the northern lowlands.
The current age may be dated from the time the existing poles were formed.
Narrow angle images
Previous poles have left many changes on the Martian surface. To examine smaller scale changes I have examined 730 MOC narrow angle images out of a larger randomly acquired collection, separating them into various kinds of formations such as water signs, dunes, and layers. These were accumulated over several years, before the ideas in this paper were conceived so there is no relevant unconscious bias in their selection.
This gave a list of coordinates between 0, equal to 90 degrees old north and 180 which is 90 degrees old south.
Fluid signs gave an unusual distribution with a large number clustering around the Pole 4 equator. On further examination these were around 37 to 43S and 140 to 200W, and 39N 19W.
The first cluster is on the bottom edge of an ice ridge area identified by Odyssey, which abuts the old equator at these coordinates. This was previously identified as Pole 3. The second cluster abuts another ice rich area on the top, again on the old equator and also near the dichotomy boundary. This is at the opposite Pole 3.
The water could have several possible origins. Some ravines could have formed on this pole, but this is unlikely as it should be very ancient and the water flows are more recent. The second possibility is these flows occurred on the equator of Pole 4 because it was warm enough there for some water to melt from the remaining ice of Pole 3. In that case we may be seeing relics of this flow. The third possibility is we are seeing ice from Pole 3 melting because the current latitudes are suitable for this. In all cases this implies the source of the water was ground water or ice in the soil from Pole 3.
Since the water only seems to have been flowing in small areas it seems likely that these areas started flowing on the equator in Pole 4 in a restricted area close to the equator. Though the pole has shifted channels in the ground are still connected to this ice, and at certain mid latitudes this can still flow . As we will see the positions of gullies is also correlated with layering relative to Pole 4. Hartmann et al compare these gullies with Icelandic gullies, which is consistent with the idea of seepage from a former polar area.
Others seem to cluster around 35S 270W, and 29S 38W. The first cluster is on the north eastern edge of Hellas Basin and may represent an area on the eastern edge of the South Pole 4 ice cap.
The second cluster is close to the south western edge of the South Pole 3 ice cap and so is likely to have formed with the same mechanism. This then gives all 4 main clusters the same mechanism, of ice from an old pole now at mid latitudes suitable for a water flow.
Another cluster is at 37 to 53S 320 to 356W. This is close to South Pole 4. Again the mechanism seems to be a part of the ice from an old pole position which corresponds to the suitable latitude for water to flow now.
It would seem then the reason the craters with water signs are so rare is that old polar ice deposits and suitable current mid latitude temperatures only coincide at a few positions.
Schmidt points out additional areas with craters, which are also examined.
Gorgonum Chaos  is situated at 37S 173W, which would be on the southern edge of North Pole 3. Wilson et al believe these gullies are not so young and represent only a limited discharge. This would be consistent with the older position of Pole 3, which still had to move to Pole 4 and on to the current Pole 5. One theory according to Moore et al is that these knob fields were formed by water and near a lake, which would also be consistent with a previous Pole 3 position.
Stewart et al examine the idea that CO2 could have formed these channels, which is also consistent with a pole position. This would depend on the temperatures of Pole 3 at the time. As seen earlier the pole may have cooled in its movement from Pole 2, as the number of channels may have diminished. The temperatures may have risen after the Hellas impact as the Pole moved northward to the North Pole 4 position around then to be formed Alba Patera. Many of the objections to CO2 arise from not having a mechanism to maintain enough of it long enough to create these formations, however a pole may be able to supply this reservoir. There may be then in some of these areas a mixture of the two kinds of erosion, without knowing the temperature at the time it is probably not possible to determine. Other ravines may be more recent.
Newton Crater is situated at 41.1S 159.8W, also on the edge of the North Pole 3 area. Cabrol et al refer to the large amounts of water released into Newton Crater, which represents the dilemma of abundant water on such a dry planet. Being on the edge of a pole however could supply this water while non polar areas could remain dry.
Tempe Terra  is found at approximately 42N 73W. This area would again have been on the edge of an ice cap, in this case North Pole 4. Volcanism in the area may have come from the Hellas impact, like Alba Patera. Hauber et al point out chaos similar to Gorganum Chaos, which is also on the edge of a former pole. Syria Planum, associated with South Pole 2 also has these formations. Even though these three formations are relatively close to each other, each could have been formed from a different pole. They also show signs of glaciation, which is consistent with the edge of a pole.
Nirgal Vallis  is approximately at 27.5S 317W, on the edge of South Pole 4 near Hellas Basin. This may account for its appearance of having water more recently. Lee and Rice compare Nirgal Vallis to Devon Island, and find indications of the decay and retreat of an ice cover, consistent with the edge of a Martian South Pole 4.
Hale Crater  is located at 36S 37W. This may have experienced outflows from Argyre basin when South Pole 2 was moving eastward. Alternatively it could have received water from South Pole 1 and the movement to South Pole 2. This could have been a slow movement and generated a lot of water in this area.
Maunder Crater is on the south western edge of South Pole 4.
Rabe crater is situated at 44S 325W, which is around the area of South Pole 4.
Dao Vallis is located at 33S 266W, on the north eastern edge of South Pole 4. Arfstrom interprets the area as glacial, which is consistent with being on the edge of a pole. He believes this may be part of a larger ice flow.
All these areas referred to by Malin et al are on previous pole positions. This makes it likely groundwater rather than snow is the cause of these gullies and viscous flow features, though snow  may also be forming more easily in shapes made by flowing water. In some cases CO2 from previous poles may also have formed gullies.
Schorghofer et al map locations of slope streaks, and one cluster is approximately on South Pole 3. This may imply they are indeed related to water. Other areas tend to follow the path of the opposite North Pole 2 to North Pole 3, and then part of the movement to North Pole 4 around Alba Patera. Residual ice in the soil may also make it conducive to landslides.
Palermo et al believe these are more likely to be fluid flows. No actual gullies seem to be formed with streaks though a fluid reservoir implies they should flow over and over at least sometimes. The shapes probably represent the path to lower elevations water or dust would take.
Over time water should make some kind of mark or channel on the surface like we see in even in Russell Crater on sand. Moisture from underground ice deposits could cause landslides, and explain the link between old pole areas and the streaks. Sullivan et al point out the streaks are similar to snow avalanches, which may be consistent with icy soil under a dusty surface layer. It may be fluid flows and dust avalanches both occur at times. Sullivan et al refer to dust avalanches as the most likely explanation.
Another possibility is a small area of ice sublimates and the resulting vapour dislodges some dust and creates the landslide. If so then an example of this may have been imaged. MOC photo AB102003 shows a possible plume of vapour found by Spires, colloquially known as “Dan’s smoker”. There is a slope streak in this image pointing in the same direction, and other images in the area such as M2300332 contain slope streaks. The pale mark seems to go down one mound and then climb the other, which makes it unlikely to be a streak. If this was reimaged and the light streak was gone then it is more likely to have been vapour. E1103683 just misses this formation.
Hematite has been found in the area of South Pole 3, which is consistent with the having water around a polar area. The area is believed to have been recently exhumed, by Lane et al which is consistent with the pole moving and exposing this area. According to Hynek Aram Chaos and Valles Marineris  also have hematite deposits, which is consistent with the path of the moving pole from South Pole 2 to South Pole 3 giving water to create hematite. Aram Chaos is to the west of the South Pole 3 position and is connected to the Areas Valles outflow channel. This would also be consistent with the pole depositing water as it moved.
Images of dunes were also compared to their Pole 4 latitudes. Dunes were generally found to be evenly spread around the current pole longitudinally and to be confined within 40 degrees north and south of the current equator. The distribution in regard to Pole 4 was also even but generally from 50 degrees north to 50 degrees south. This is an usual correlation as Pole 4 is at 45 degrees south, and so the distribution should be skewed. This implies that dunes formed in a band between 50 degrees old north and 50 degrees old south in relation to Pole 4. In turn this implies a high enough air pressure for dunes to form at the time. After the pole shift the dunes would appear to be moving to the same kind of formation relative to Pole 5.
Dunes on the current South Pole 5 were also examined. These dunes were typically found between 75 to 85S and 100 westward to 350W. In relation to South Pole 4 all of these dunes were found to be between 30 and 50 degrees old south (that is, south compared to Pole 4) which implies they were actually formed before the Pole shift of Pole 4 to the current Pole 5. If so then these dunes may have been frozen in position since then. Malin et al say there is no evidence dunes on Mars are presently mobile.
Layer images were also examined and mainly fell in the old southern hemisphere of South Pole 4, particularly from the equator to 50 degrees old south (old south is relative to Pole 4). This is surprising as it implies much of the layering shown was actually formed under Pole 4 though earlier layers may be buried.
Layers found on the current South Pole, Pole 5, were typically at 85S and concentrated at 175 to 275W. This in relation to South Pole 4 placed them between 30 and 50 degrees old south, also implying they were formed in the time of Pole 4 rather than on the current pole. Malin et al point out layers in Candor Chasma, which is near the equator of Pole 4 seems relatively young compared to nearby Arsia Mons. The absence of craters may imply these layers were made in the time of Pole 4, or perhaps exhumed by processes in that time.
If so then much layering has been a relatively recent occurrence associated with the Hellas impact, perhaps because older layering may have been buried. Pole 4 may have existed for long enough for layers under it to dominate.
Dunes and layers have a similar distribution in the southern hemisphere of Pole 4, while water signs seem to be related to different poles. It may be then that air rather than water is responsible for many of these layers. CO2 may also have formed some layers, if the temperature dropped enough. The change from Pole 4 to Pole 5 may have occurred when the temperature dropped enough to freeze the air, so ice sublimated and went to the poles
If the air pressure dropping was enough to make the pole move to Pole 5 then that implies it had not dropped to that level earlier, or the pole shift would have already happened. The dropping of the temperature then may have represented a final phase change, or the temperatures may have periodically risen with changing obliquity. If so then the pole may have wandered to some degree between the positions of Pole 4 and Pole 5 depending on the level of ice depositions in the northern lowlands.
In this time CO2 may have been involved in the formation of layers. Odyssey thermal data implies layers were not formed by water. Layers are found in the area of Pole 3, which may have formed in that time just as some layers form on the poles today. Layers could have formed under all the previous poles; it may be that Pole 4 dominates because it is the most recent.
Some layers may have been formed in the movement of Pole 2 to Pole 3, and because this is on the dichotomy boundary this will appear in the equatorial region of Pole 4. Also since Tharsis Montes, Olympus Mons, Hecates Tholus, Elysium Mons and Alba Tholus all are near the Pole 4 equator in the time ash may form layers also appearing to be caused by Pole 4. Some layers may also have been formed along the equatorial region of Pole 4 by water if the temperature was high enough.
In terms of astrobiology the impacts certainly warmed Mars, and depending on their timing may have created a climate that could have supported life for long periods.
In an ideal scenario the Utopia impact would have heated the planet for a long time, as ice and CO2 forming in the Utopia Basin would have been warmed. Since even now Mars is close to being warm enough to sublimate all the CO2 from the poles it is reasonable to believe that this impact basin at the pole would have made it warm enough to raise the air pressure, especially with higher obliquity.
If the Isidis impact occurred before the planet cooled then this would have added heat, as Pole 2 forming on Isidis Basin would have sublimated CO2, as would the pole opposite it around Solis and Syria Planum.
Next the Argyre impact may have warmed the poles followed by the Hellas impact. If these were spaced at the right times then Mars may have had a long time of higher air pressure and occasional liquid water. These conditions would possibly have allowed microbial and even substantially more evolved life forms to survive, especially since the higher air pressure would have offered some protection from radiation. An impact may have decimated life much like impacts did on earth but subsequently kept the planet warm enough for the survivors to adapt. If the Hellas impact destroyed the Martian magnetic field then this could have led to the extinction of some life. Without sufficient life to create oxygen this may have led to the air freezing more as CO2 and ice sublimating to the poles.
Eventually the impacts and volcanoes ceased and life if it still or ever existed would have had to adapt to the much colder climates.
The more likely scenario is that life may have evolved somewhat during these times of higher temperatures only to die off or survive at a low level when the planet cooled and the air froze. With the next impact some life may have evolved again if the times were long enough, perhaps being reseeded with meteors from Earth.
Much of the Martian terrain is consistent with the idea of polar wander. This may have been controlled by 4 main impacts, Utopia, Isidis, Argyre, and Hellas.
The Isidis impact may have formed some of the deformations around Solis and Syria Planum.
The impact of Argyre may explain the formation of the Tharsis Montes, Olympus Mons, Elysium Mons, Hecates Tholes, and Alba Tholus.
The movement of Pole 2 to Pole 3 may explain the formation of the dichotomy boundary and all the fluid channels north of it. It may also have formed the Northern Lowlands.
The number of narrow angle images examined here is too small to give a definite conclusion, but they give a picture of Pole 4 having a large influence on many current Martian features. This may be an artefact of the selection process but they were accumulated well before the ideas in this paper.
Fluid signs in craters and valleys are found on the edges of older poles, which are now at suitable latitudes for water ravines to form.
Some dunes are found to be evenly spread compared to Pole 4, even on the current South Pole 5 and imply a time of higher air pressure, and perhaps that since then there has been insufficient air pressure to move them from this pattern.
Layering may have partially occurred in the time of Pole 4, and some layers on the current South Pole may be from before the pole shift to Pole 5.
 Bradley J. Thomson and James W. Head III “Utopia Basin, Mars: Characterization of topography and morphology
and assessment of the origin and evolution of basin internal structure” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. 0, PAGES 1–22, MONTH 2001 http://www.planetary.brown.edu/planetary/documents/2396.pdf
See Figure 1, comparing Utopia Basin with Hellas Basin.
NASA, Jack Connerney, Mario Acuna, Carol Ladd “Martian Magnetic Map”
 “The northern hemisphere is made up largely of rolling volcanic plains, not unlike the lunar maria. These extensive lava plains—much larger than those found on Earth or the Moon—were formed by eruptions involving enormous volumes of lava. They are strewn with blocks of volcanic rock as well as with boulders blasted out of impact areas by infalling meteoroids (the Martian atmosphere is too thin to offer much resistance to incoming debris). The southern hemisphere consists of heavily cratered highlands lying several kilometers above the level of the lowland north.”
“On the basis of arguments presented in Chapter 8, this smoother surface suggests that the northern surface is younger. (Sec. 8.4) Its age is perhaps 3 billion years, compared with 4 billion in the south. In places, the boundary between the southern highlands and the northern plains is quite sharp. The surface level can drop by as much as 4 km in a distance of 100 km or so. Most scientists assume that the southern terrain is the original crust of the planet. How most of the northern hemisphere could have been lowered in elevation and flooded with lava remains a mystery.”
Nanjing University Syllabus “The Surface of Mars available online at
 “Major features of topography. The dominant feature of the topography is the striking difference (;5 km) in elevation between the low northern hemisphere and high southern hemisphere that represents one of the outstanding issues of martian evolution. This hemispheric dichotomy also has a distinctive expression in the surface geology of Mars. The surface of the crust in the southern hemisphere is old and heavily cratered,
whereas that in the north is younger and more lightly cratered and was probably volcanically resurfaced early in Mars’ history (17). The
hemispheric difference is also manifest in surface roughness (Fig. 3) calculated from the MOLA topographic profile data (18). Most of the northern lowlands is composed of the Late Hesperian–aged (19) Vastitas Borealis Formation, which is flat and smooth (Fig 2), even at a scale as short as 300 m (Fig. 3). The Amazonian-aged (19) Arcadia Formation, which overlies the Vastitas Borealis Formation, is also smooth at large and small scales, consistent with either a sedimentary (4, 20) or volcanic (21) origin for these plains. In the southern hemisphere Noachian aged (19) ridged plains form locally flat intercrater deposits, whereas younger Hesperian- aged ridged plains dominate in some regions. All are characterized by a rougher topography than the northern plains. The boundary between the smooth northern hemisphere and the rough southern hemisphere is characterized by mesas, knobs, and intervening
plains (22), as well as regional elevation changes of up to 4 km over distances of 300 to 1300 km (23). Where the regional elevation change is relatively steep, it is referred to as the dichotomy boundary scarp (compare Fig. 1).” Smith, D.E. et al “The global topography of Mars and implications for surface evolution” Science, 284, 1495-1503, 1999 available online at http://ltpwww.gsfc.nasa.gov/tharsis/global_paper.html
 “Very roughly speaking, this is a map of the ages of the surfaces on Mars. The red surfaces were formed in period 1, the green surfaces were formed in period 2, and the blue surfaces were formed in period 3. These three periods correspond roughly to the three Martian periods Noachian, Hesperian, and Amazonian (named after regions that approximate those ages.)” Mike Caplinger” Determining the age of surfaces on Mars” Malin Space Science Systems February 1994 available online at http://www.msss.com/http/ps/age2.html [16/8/03]
 Jarmo Korteniemi “Main albedo features and full nomenclature” available online at http://www.student.oulu.fi/~jkorteni/space/mars/maps/ [16/8/03]
 USGS Astrogeology Research program Regional MOLA map available online at
 K. F. Sprenke and L. L. Baker “POLAR WANDERING ON MARS?” Lunar and Planetary Science XXXI 1930.pdf
 “Gravity over the north polar region (Fig. 4A) reveals several positive anomalies that have no obvious correlation with topography (16). A combination of ice and crustal material has been proposed (17) to account for anomalies situated in the immediate vicinity of the north polar layered terrains. In contrast, the south polar region (Fig. 4B) shows a positive anomaly of ;200 mgal immediately over the pole, which
could represent the load associated with the permanent ice cap. The lack of a comparable anomaly over the northern cap could indicate that the southern cap is younger and has not yet had sufficient time to adjust isostatically, or that the southern layered deposits contain a larger
fraction of dust, thus constituting a greater gravitational load than in the north (12).
A possible explanation for the high-latitude northern hemisphere gravity anomalies, adjacent to and remote from the residual ice cap, is that they represent moderate-diameter (100 km) impact basins buried beneath the resurfaced northern hemisphere (18). The mass excesses implied by these positive anomalies may represent a combination of volcanic and sedimentary fill within the basin cavity and thinning of the northern hemisphere crust beneath the basin (19) that have not relaxed to an isostatic state (20).” David E. Smith et al “The Gravity Field of Mars:
Results from Mars Global Surveyor” available online at
 “We find evidence for several probable buried basins in the lowlands and at least one in the highlands that are similar to Hellas, Argyre, Isidis, Chryse and Utopia in size. All of these buried features must be extremely old because smaller likely buried basins are superimposed on them. We previously used this relationship to suggest Utopia was "Earliest" Noachian in age.” FREY, Herbert V “LARGE BURIED AND VISIBLE BASINS ON MARS: TOTAL POPULATION AGES OF THE HIGHLANDS AND LOWLANDS”
 “Abstract. Recently obtained Mars Orbiter Laser Altimeter (MOLA) topography has permitted a new assessment of the morphology, structure, and history of Utopia Planitia. The new topographic data convincingly demonstrate that the Utopia region is an impact basin, as originally proposed by McGill , whose major topographic expression is a circular, 1–3 km deep depression _3200 km in diameter. Utopia Basin is the largest easily recognizable impact structure in the northern hemisphere of Mars and is the only portion of the northern lowlands that exhibits a distinct large-scale impact signature; its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the Noachian period.” Bradley J. Thomson and James W. Head III “Utopia Basin, Mars: Characterization of topography and morphology
and assessment of the origin and evolution of basin internal structure” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. 0, PAGES 1–22, MONTH 2001
 “After Isidis, the largest impact-associated gravity anomaly (Table 2) is Utopia (Fig 5A), which has been interpreted as an ancient basin on the basis of surface geology (24). Topographic data indicate that the basin is a quasi-circular depression;1500 km in diameter (25), a factor of about 2 greater than originally proposed. Utopia’s gravity anomaly
is diffuse, occupying an area of ;107 km2 with no clear centre. The Utopia structure is buried beneath the northern hemisphere resurfacing,
but the size of the depression and gravity anomaly suggest that the original basin could have been of a size comparable to that of Hellas (Fig. 5B) (16). However, these two massive structures appear in complete
contrast gravitationally. Both appear to have readjusted isostatically, but Utopia was subsequently filled with material, which contributes
to the gravitational mass excess. If the Utopia and Hellas structures were originally similar, the gravity field data may be able to shed light on the density of the material that has filled Utopia and by inference on the material of the northern plains.” David E. Smith et al “The Gravity Field of Mars: Results from Mars Global Surveyor” 1 OCTOBER 1999 VOL 286 SCIENCE www.sciencemag.org available online at
 “8.5. Open Water Features
Parker et al.  presented evidence for as many as seven
contacts between the northern plains and southern uplands, which
were interpreted to be highstands of a former ocean. On Earth,
wave-cut platforms and associated landforms result from direct
coupling of wind and the open water surface [Duane et al., 1972;
Swift et al., 1972, 1973; Stubblefield et al., 1975; Swift, 1975;
8.6. Ice-Dominated Bodies of Water
A second possible analog for the circumferential features
includes the extremely wide, near-horizontal platforms that are
common in high-latitude regions on Earth. Known as strandflats,
they are up to 50–60 km wide and have extremely low crossplatform
gradients [e.g., Evers, 1962; Benn and Evans, 1998].
There have been many theories advanced for their formation, but
many workers have highlighted the importance of frost shattering
[Nansen, 1904, 1922; Larsen and Holtedahl, 1985; Guilcher et al.,
1994]. Frost action resulting from recurrent freeze-thaw cycles is
an effective geomorphologic agent and is considered to be a key
component of rapid coastal cliff recession and platform extension
in polar seas [Hansom, 1983; Matthews et al., 1986]. The most
extensive strandflats are found in areas sheltered from wave
erosion [e.g., Hansom, 1983]. An ice foot, or accumulation of
sea ice frozen onto the shoreline, inhibits erosion by wave action
during freeze periods but may increase the potential for frost
shattering at the base of coastal cliffs [Nansen, 1922; Feyling-
Hanssen, 1953; Nielsen, 1979]. Exposure of the coastline to wave
action during thaw periods may increase the rate of platform
formation by facilitating the removal of debris [Matthews et al.,
1986]. An idealized cross section of terrestrial strandflat generations
is given in Figure 12. Note that the sequence of landforms
shown is of similar scale to the circumferential features shown in
Utopia [see also Rice, 2000].” Bradley J. Thomson and James W. Head III
“Utopia Basin, Mars: Characterization of topography and morphology
and assessment of the origin and evolution of basin internal structure” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. 0, PAGES 1–22, MONTH 2001
 “Viking Orbiter and Mars Orbiter Camera images show mesas having horizontal to angled layers in many Valles Marineris chasmata. Several chasmata are filled nearly to the plateau rim with Late Hesperian to Early Amazonian  interior deposits, many of which are separated from
the chasmata walls by a moat. A lacustrine origin was suggested because of their apparent horizontal continuity and similarity in connected troughs [2,3,4,5,6,7]. Others prefer a volcanic origin based on the volcano-tectonic setting, layer diversity, low albedo and high competence of some layers, tuff-like weathering, and location of dark materials [1,4,8,9]. The interior deposits of Gangis and Juventae Chasmata were suggested to be similar to the ideal tuya form (table-like) 10] and eroded flutes and variable albedo of Hebes Chasma deposits bear an uncanny resemblance to tuyas . We note that Mars Orbiter Laser Altimeter data show interior deposits that locally (1) reach 4-km in height, (2) rise above sections of plateau, and (3) in the case of
Hebes, have the distinctive tuya form. Their morphologies include local resistant caps , ridged forms, and possible deltas. Based on the dimensions, morphologies, and associated catastrophic floods and other geologic events (glacial, tectonic, and mass flows) we support the suggestion that the interior deposits are hyaloclastic ridges and tuyas.” Page 15 Volcano/Ice Interaction Workshop August 13-15, 2000 ReykjavÍk, Iceland available online at
 “Valles Marineris shows a strong negative anomaly congruent with the topography (Fig 6). The rift axis anomaly is the largest negative
gravity feature on Mars and is due mostly to the mass deficit associated with the chasm (29), which has a depth of 11 km below the surrounding
terrain at its lowest point (12). The canyons are flanked by gravity highs but the canyon system lacks a negative anomaly, broader than
the rift, that is associated with upwelling of hot mantle material beneath active rifts on Earth (30). The deviation of the canyon from isostatic compensation is consistent with its formation subsequent to Argyre and Hellas (31) and suggests that the martian lithosphere has not yet adjusted to its presence.” David E. Smith et al “The Gravity Field of Mars: Results from Mars Global Surveyor” available online at
 Fig 6 David E. Smith et al “The Gravity Field of Mars:Results from Mars Global Surveyor” available online at http://ltpwww.gsfc.nasa.gov/tharsis/smith.mgs.grav.pdf
 Fig 1a David E. Smith et al “The Gravity Field of Mars: Results from Mars Global Surveyor” available online at
 “Clusters of small cones on the lava plains of Mars have caught the attention of planetary geologists for years for a simple and compelling reason: ground ice. These cones look like volcanic rootless cones found on Earth where hot lava flows over wet surfaces such as marshes, shallow lakes or shallow aquifers. Steam explosions fragment the lava into small pieces that fall into cone-shaped debris piles. Peter Lanagan, Alfred McEwen, Laszlo Keszthelyi (University of Arizona), and Thorvaldur Thordarson (University of Hawaii) recently identified groups of cones in the equatorial region of Mars using new high-resolution Mars Orbiter Camera (MOC) images. They report that the Martian cones have the same appearance, size, and geologic setting as rootless cones found in Iceland. If the Martian and terrestrial cones formed in the same way, then the Martian cones mark places where ground ice or groundwater existed at the time the lavas surged across the surface, estimated to be less than 10 million years ago, and where ground ice may still be today.” Linda M.V. Martel “If Lava Mingled with Ground Ice on Mars” PSR Discoveries [6/26/01] available online athttp://www.psrd.hawaii.edu/June01/lavaIceMars.html
 H. V. Frey, S. E. H. Sakimoto, and J. H. Roark “MOLA TOPOGRAPHY AND THE ISIDIS BASIN: CONSTRAINTS ON BASIN CENTER AND RING DIAMETERS” LPSC98 available online at
 Figure 1a
 “3) a site at ~5°S and 264°W just south of the Isidis rim that is heavily dissected by channels. These regions were optimally imaged by Viking for the generation of DTMs, lie within the Mars 2001 landing constraints, and are potential locations for fluvial or lacustrine deposits. Our initial analysis of the later sites indicates that fluvial erosion for large solitary channels probably took the form of sapping, whereas denser networks of small channels may have formed at least in part from runoff, such as from surface ice-melt. Both sites show that channeling took place during a period in which fairly large craters will still forming. The tectonic fabric appears to largely predate the channeling. Aeolian deposition largely post dates the channeling.”
J. M. Moore (NASA Ames), A. D. Howard (U. Va.), P. M. Schenk (LPI) “[43.04] The Topography and Basin
Deposits of the Equatorial Highlands: A MGS–Viking Synergistic Study” 31st
Annual Meeting of the DPS, October 1999
Session 43. Mars Surface: Structure available online at
 J.A.Iluhina and J.F.Rodionova “AUTOMATED MAKING THE MAP OF ISIDIS’S BASIN” Microsymposium 36, MS037, 2002 available online at
 “Beagle 2 has as its focus the goal of establishing whether evidence for life existed in the past on Mars at the Isidis Planitia site or at least establishing if the conditions were ever suitable.” Page 4 J. D. Farmer “Exploring for Martian Life: Recent Results and Future Opportunities” Astrobiology Volume 1 Number 3  available online at http://188.8.131.52/search?q=cache:XenIThQGrU8J:cips.berkeley.edu/events/discussion_group_2003_spring/farmer_astrobiology_space_missions.pdf+farmer_astrobiology_space_missions.pdf&hl=en&ie=UTF-8
First image Ames Research Centre available online at http://amesnews.arc.nasa.gov/releases/2002/02images/mars/mars.html
 "When the river valleys on Mars were confirmed in the 1970s, many scientists believed there once was an Earth-like period with warmth, rivers and oceans," said Owen Toon, a professor at the University of Colorado and a coauthor of the Science paper. "What sparked our interest was that the large craters and river valleys appeared to be about the same age." Another piece of evidence arguing against a condition warm, wet period on Mars are images of river channels without any sign of tributaries flowing into the main channel. "We definitely see river valleys but not tributaries, indicating the rivers were not as mature as those on Earth," said Toon. Jeff Foust “New research explores past, present water on Mars” Spaceflight Now December 5th 2002 available online at http://spaceflightnow.com/news/n0212/05mars/
 Nancy Ambrosiano “Los Alamos releases new maps of Mars water” Los Alamos National Laboratory  available online at
 M. L. Litvak “DISTRIBUTION OF CHEMICALLY BOUND WATER IN SURFACE LAYER OF MARS BASED ON DATA ACQUIRED BY HIGH ENERGY NEUTRON SPECTROMETER, MARS ODYSSEY” Microsymposium 36, MS062, 2002
“ Koroshetz and Barlow , using Viking Orbiter imagery, found smaller onset diameters for SL morphology craters in the Solis Planum region south of Valles Marineris (20S-30S 50W-90W), one of the same
regions where  found a higher concentration of ML morphologies. Koroshetz and Barlow propose that the uplift of the Tharsis Bulge, directly west of this region, caused the water table in this area to tilt and the water flowed into a topographic depression south of
Valles Marineris.” N. G. Barlow “SUBSURFACE VOLATILE RESERVOIRS: CLUES FROM MARTIAN IMPACT CRATER MORPHOLOGIES” Fifth Conference 1999 http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6082.pdf
 “A group of scientists claims to have found evidence of liquid water under the surface of Mars. The team, led by Nadine Barlow of the University of Central Florida’s Robinson Observatory, believes the reservoir lies relatively close to the surface, at a depth of roughly 110 meters (360 feet).” Ames Research Centre “Mars Watering Hole Found, Scientists Say” available online at
 “Our current study suggests that the ice-rich layer producing the SL morphology lies closer to the surface (<300 to 500 m) in the Solis Planum region than elsewhere in the equatorial region (~520-572 m) and that an underlying liquid reservoir, which produces the ML morphologies, has been present since the region formed in the Hesperian.” N. G. Barlow, C. B. Perez (U. Central Fl.), J. Koroshetz (U. Fl.) “[39.06] A Volatile-Rich Reservoir South of Valles Marineris, Mars” 31st Annual Meeting of the DPS, October 1999 Session 39. Mars Surface: Evidence of Change available online at http://www.aas.org/publications/baas/v31n4/dps99/40.htm
 “We propose that the uplift of the Tharsis Bulge to the west of this region warped the area and tilted a pre-existing groundwater table. The tilting of the groundwater table caused the volatiles to accumulate in the slight depression where today the smaller onset diameters and abundance of ML morphologies are found.” Ibid.
 “8.4. Glacial Features
Another possible explanation of the circumferential features is
that they are related to morainal/ice-margin features. A glacial
explanation has been advanced for the formation of thumbprint
terrain [Lucchitta, 1981; Rossbacher, 1985; Lucchitta et al., 1987;
Scott and Underwood, 1991; Scott et al., 1992; Kargel and Strom,
1992; Kargel et al., 1995]. As shown in Figure 10, there are areas of
thumbprint terrain that are located in the middle of the zone of
circumferential features in southern Utopia. On the basis of the
morphology and distribution of thumbprint terrain and other structures,
several workers have suggested the former presence of large
ice sheets in the northern hemisphere of Mars [Lucchitta et al.,
1986; Chapman, 1994; Kargel et al., 1995]. The lack of associated
glacial flow features such as drumlins in the northern plains seems
inconsistent with widespread glacial activity. Drumlins are streamlined
mounds of glacial till that have elongated teardrop shapes in
plan view [Benn and Evans, 1998]. The absence of drumlins does
not rule out a glacial explanation, for a glacial body in the northern
hemisphere may have been cold-based for much of its evolution
[e.g., Kargel et al., 1995]. However, the lack of drumlins highlights
the general lack of features related to mass ice movement and scour
in the interior of the Northern Plains. In addition, because ice
experiences a drop in plasticity with decreasing temperature [Glen,
1955; Goldsby et al., 2001], the current temperature regime on Mars
would tend to inhibit glacial flow. This does not exclude the possibility of glacial activity at periods of high obliquity or more
temperate paleoclimatic conditions but highlights the need for a
greater understanding of ice deformation mechanisms [Goldsby et
al., 2001] under possible Martian paleoclimates before the viability
of a glacial explanation can be verified.” Bradley J. Thomson and James W. Head III “Utopia Basin, Mars: Characterization of topography and morphology and assessment of the origin and evolution of basin internal structure” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. 0, PAGES 1–22, MONTH 2001 available online at
 “Evidence for a large ground water reservoir
-- capped by a relatively shallow layer of ice -- exists within the Mars'
Solis/Thaumasia Planum region, says a team of scientists. The site is south of
the huge Martian canyon system, Valles Marineris.” Leonard David “Mars
Watering Hole Found, Scientists Say” Space.com posted: 03:00 pm ET
13 August 2001
“ We propose that the strain from Syria Planum was transferred along proto-Valles Marineris forming a sinistral transtensional zone which provided tectonic control for later valles formation. At the east end of Valles Marineris, the Coprates Rise is a lithospheric buckle with a thrust fault along the eastern edge. We also interpret the southern edge of the Thaumasia Highlands as the surface exposure of a thrust fault. The compressional structures of the Coprates Rise appear to extend into the Thaumasia Highlands. The thrust faults likely cut deep into the crust and may represent the décollment for later wrinkle ridge faulting in Sinai and Solis Planum. In this hypothesis, Claritas Fossae represents a dextral transpressional zone and acts as a boundary between the eastern and western halves of the south-Tharsis ridge belt identified by Schultz and Tanaka (1994, JGR 99, p. 8371), which includes the Coprates Rise, Thaumasia Highlands, and ridges in Daedalia Planum. Compression in Daedalia Planum likely resulted from the same forces affecting the Thaumasia Plateau in the Noachian, but was arrested at an earlier stage of development, perhaps due to the buttressing effect of early Tharsis Montes construction.” WEBB, Benjamin M. “NOACHIAN TECTONICS OF SYRIA PLANUM AND THE THAUMASIA PLATEAU” Paper No. 132-0  available online at http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_28019.htm
 “Summary: It is argued that Syria, Sinai and Solis
Plana were generated by the volcanic activity associated with a mantle plume. They formed a large lithospheric root which was removed in a convective downwelling initiating a buoyant rebound of the region, followed by later subsidence when this uplift could no longer be sustained. The sequence of faulting within the region  is consistent with this scenario.” Evelyn D. Scott “SUB-LITHOSPHERIC ‘SUBDUCTION’ ON MARS: CONVECTIVE REMOVAL OF A LITHOSPHERIC ROOT. III: SYRIA PLANUM REGION” Lunar and Planetary Science XXXI 1331.pdf http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1331.pdf
 “This hypothesis easily combines the various hypotheses that Valles
Marineris formed either as a thermal response to events in the Martian mantle or as a tectonic response to the loading of Tharsis. If it is argued that there is an asthenospheric upwelling below the Plana, then the Wernicke 'Simple Shear' model can be invoked to explain the opening of Valles Marineris. In this model the upwelling is lateral to the site of the rifting, whereas McKenzie's 'Pure Shear' model would locate the site of rifting immediately above the mantle decompression. The fact that the fissure system of Noctis Labyrinthus has not evolved to the same extent as that of Valles Marineris could be because it is not as close to the thermal influence of the upwelling or because it has formed simply as a response to the isostatic realignment and was not influenced to as great an extent by the growth of the Tharsis volcanic shields.” Ibid.
 “The new topographic data illuminate a long-standing debate over the dominant contributors to the high elevations of the Tharsis region. A prominent ridge (containing Claritas Fossae; Fig. 2) extends southward from the region of the Tharsis Montes, and then curves northeastward in a “scorpion tail” pattern. This arcuate ridge bounds Solis Planum, a plateau within the southern rise. The ridge contains an abundance of heavily cratered Noachian material that has presumably escaped resurfacing by younger Tharsis volcanic flows because of its high elevation. It has been suggested (25) that the termination of the ridge structure could have formed by lithospheric buckling, as could, by analogy, other ridge structures in the south Tharsis region. The southern rise (southward of ;35°S) also contains exposures of heavily cratered Noachian units. These elevated ancient terrains are consistent with the view that the broad expanse of the southern rise (elevations .;3 km; see Fig. 2) formed at least in part by structural uplift (26). David E. Smith “The Global Topography of Mars and Implications for Surface Evolution” www.sciencemag.org SCIENCE VOL 284 28 MAY 1999 available online at
 MSSS “Wide Angle View of Arsia Mons Volcano” MGS MOC Release No. MOC2-179, 27 September 1999 http://mars.jpl.nasa.gov/mgs/msss/camera/images/9_27_99_arsia/
 Calvin J. Hamilton “Arsia Mons” 1997 available online at
 “Surface environmental conditions on Mars are presently extremely cold and hyperarid, most equivalent to polar deserts on Earth. Coupling newly acquired Mars MOLA and MOC data with field-based observations regarding the flow, surface morphology, and depositional history of polar glaciers in Antarctica, we show that the multiple facies of an extensive fan-shaped deposit on the western flanks of Arsia Mons, Tharsis Rise are consistent with deposition from cold-based mountain glaciers. An outer ridged facies that consists of multiple laterally extensive, arcuate and parallel ridges, resting without disturbance on both well-preserved lava flows and an impact crater, is interpreted as drop moraines formed at the margin of an ablating and predominantly
receding cold-based glacier. Inward of the ridges lies a knobby facies that consists of irregular and closely spaced equidimensional knobs, each up to several kilometers in diameter; this facies is interpreted as a sublimation till derived from in situ downwasting of ash-rich glacier ice. A third facies comprising distinctive convex outward lobes with concentric parallel ridges and aspect ratios elongated downslope likely represents rock-glacier deposits, some of which may still be underlain by a core of glacier ice. Taken together, these surficial deposits show that the western flank of Arsia Mons was occupied by an extensive mountain glacial system accumulating on, and emerging from, the upper slopes of the volcano (above ˜7000 m) and spreading downslope to form a piedmont-like fan. Similar deposits exist on the other Tharsis Montes, suggesting at least one phase of late Hesperian aged glaciation in the equatorial Tharsis region.” J. W. Head , D. R. Marchant “COLD-BASED MOUNTAIN GLACIERS ON MARS: WESTERN ARSIA MONS” Geophysical Research Abstracts, Vol. 5, 02770, 2003
c European Geophysical Society 2003 available online at
 “Using new MGS data and Earth analogs appropriate for Mars, we explored the hypothesis that the deposit is the remnant of a mountain glacier formed on the western flank of Arsia Mons (e.g., ). Conditions during the recent geological history of Mars suggest that glacial ice should commonly be below the pressure melting point, and thus analogous to polar glaciers, which are frozen to underlying beds (cold-based), and move by internal deformation, producing no record of basal scour or extensive meltwater features. Glaciers in the Antarctic
Dry Valleys may be most appropriate terrestrial analogs, and we find many similarities between them and the western Arsia fan-shaped deposits. We interpret the outer parallel ridge zone to be distal
dump moraines formed from the lateral retreat of a coldbased
glacier, and the hummocky facies to be proximal hummocky moraines resulting from the sublimation, decay and downwasting of the ice sheet (a sublimation till). The arcuate structures in the proximal zone are interpreted to be rock glaciers, formed by lobate flow deformation of debris-covered ice surfaces; some rock glaciers may still be ice-cored. We find little evidence for melting features in association with the deposit, and thus conclude that it was predominantly cold-based throughout its history. In summary, we find abundant evidence to support the interpretation that the fanshaped western Arsia Mons deposit was formed by a cold-based mountain glacier. Similar deposits are seen
on Pavonis and Ascraeus Montes.” James W. Head and David R. Marchant “MOUNTAIN GLACIERS ON MARS?: WESTERN ARSIA MONS FAN-SHAPED DEPOSIT SMOOTH FACIES AS ROCK GLACIERS:” Microsymposium 36, MS103, 2002
 “Characterization: The basic units comprising Arsia Mons consist of lava flow members of the Tharsis Montes Formation [2; see also 3], and the oldest flows are Late Hesperian in age, and younger units span the Amazonian. Scott and Zimbelman  show that during the Amazonian, three lava flow members of the Tharsis Montes Formation and the three facies of the fan-shaped deposit were emplaced. The ridged facies of the fan deposit clearly overlies Member 5 and is thus considered to be Late Amazonian in age.” James W. Head and David R. Marchant “MOUNTAIN GLACIERS ON MARS? CHARACTERIZATION OF WESTERN ARSIA MONS FANSHAPED DEPOSITS USING MGS DATA:” Microsymposium 36, MS105, 2002
 “Introduction: Prominent magnetic anomalies are absent over the major volcanic edifices of Mars. Apparently the martian global magnetic field ceased to exist long before the volcanism north of the dichotomy
occurred . However, Arsia Mons, the southernmost of the great shield volcanoes of Mars, is located adjacent to a large regional magnetic anomaly (Fig.1). This raises the question of whether the Arsia Mons lavas might have acquired a magnetization induced from the much older remnant magnetization in the adjacent crust. This magnetization, induced by local fields associated with magnetized regions of the crust, would have occurred in spite of the absence of a global field at the time of emplacement.” And see Figure 1 K.F. Sprenke and L.L. Baker “Magnetization of Arsia Mons, Mars” Lunar and Planetary Science XXXIII (2002) 1070.pdf
 “Recently, it was proposed, on the basis of a morphological interpretation of Viking Orbiter images, that a thick ice sheet covers the Arsia Mons volcano in the Tharsis province on Mars, i.e. almost on the equator (Geology, March 1999, v. 27; no. 3; p. 231-234).” This conclusion is reached by examining deep canyons that cut into the fan areas of Arsia Mons and almost reach into the caldera area. These canyons are interconnected to circular vent-like structures that are interpreted as openings where ice has been melted above eruptive volcanic sites.
These vent-like openings lack a collar of ash normally associated with eruptive vents. The close association of a fissure swarm, large scale canyons, numerous vent-like structures and a broad fan area concur with a genetic relationship between these features.” Johann Helgason “Does Mars Hide Vast Water Deposits” MARSDAILY.COM SPECIAL REPORT Reykjavik - June 10, 2000 available online athttp://www.spacedaily.com/news/mars-water-00b.html
 See Figure 1 K. F. Sprenke and L. L. Baker “POLAR WANDERING ON MARS?” Lunar and Planetary Science XXXI 1930.pdf
 “Based on volume estimates of  which are based on a 3 km thick ice cap that covered the entire area of the Dorsa Argentea Formation, ~6.63 x 106 km3 of water could have been released. However, taking into account that the ice thickness very likely decreased toward the margins of the ice cap, that the ice cap contained up to 50% sediments, that not all of the melt water ended in the Argyre basin, that large amounts of ice never underwent melting but sublimed, and that large amounts of water are still stored in the pore space of the Dorsa Argentea Formation, we calculated that there is probably not enough water to completely fill the Argyre basin due to meltback of a Hesperian polar cap. We argue that partly filling the Argyre basin with water derived from polar cap meltback is more likely and is also consistent with Hesperian channels cutting far down into the basin.” H. Hiesinger, J.W. Head III
“GEOLOGY OF THE ARGYRE BASIN, MARS: NEW INSIGHTS FROM MOLA AND MOC” Lunar and Planetary Science XXXII (2001) 1799.pdf
“Catastrophic flooding out of Argyre: Uzboi Valles is a relatively large, Noachian outflow channel that cuts the northern rim of Argyre (Nereidum Montes) and drained northward toward Holden Crater, into Holden Basin . Without good topography, however, Uzboi Valles is somewhat confusing. With both ends obliterated by large impact craters and the channel floor exhibiting few streamlined forms, it isn’t even obvious which way the channel flowed. However, even the gridded MOLA topography clearly shows Uzboi probably linked the Argyre interior with Holden Basin and Ladon Valles prior to formation of the large craters (Fig. 1). Next in the system is Holden Basin , into which Uzboi Vallis flow continued prior to formation of Holden Crater . The northeast rim of Holden Basin is “gone” even though this basin superposes Ladon Basin. Instead, a broad “ramp” was identified in Viking Orbiter stereo pairs . Ladon and Arda Valles converge on this ramp and drain into the interior of Ladon Basin. Parker  inferred that the rim of Holden Basin failed catastrophically during flooding from Argyre to produce this ramp, which drained a temporary lake that had formed in Holden Basin. Continued flooding from Uzboi Vallis favored Ladon Valles’ course, so Arda Valles was quickly abandoned. Channel morphology disappears just inside the inner rim of Ladon Basin, but resumes on the basin’s northeast side, at Margaritifer Valles .”
Parker et al., , LPSC XXXI, 2033.pdf
 “Most highland basins show evidence of some communication between higher basins and adjacent, lower basins. The high plateau of Solis Planum exhibits surface drainage eastward through Her Desher Vallis–Nirgal Vallis into the upper parts of the Chryse Basin  as well as discharge westward into Amazonis as proposed by Dohm et al. .
Likewise, the Argyre basin overflowed northward through Nirgal–Uzboi Valles  into the Ladon basin and Margaritifer Basin  and eventually into Chryse Planita. The various interconnected lowlands
of Icaria Province probably spilled over the southern rim into Argyre  providing a continuous pathway from the southern polar region to the northern ocean.” R.A. De Hon “MARTIAN SEDIMENTARY BASINS AND REGIONAL WATERSHEDS” Lunar and Planetary Science XXXIII (2002) 1915.pdf
 See Figure 1 Lionel Wilson and James W. Head III “Tharsis-radial graben systems as the surface manifestation of plume-related dike intrusion complexes: Models and implications” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. E8, 10.1029/2001JE001593, 2002
 “A system of gigantic ancient valleys -- some as much as 200 kilometers wide -- lies partly buried under a veneer of volcanic lava flows, ash fall and wind-blown dust in Mars' western hemisphere. New observations made with Mars Orbiter Laser Altimeter on the Mars Global Surveyor spacecraft reveal northwestern slope valleys (NSVs) northwest of the huge martian volcano, Arsia Mons, and south of Amazonis Planitia, site of a postulated ocean.” Lori Stiles “Scientists Find Largest Flood Channels in the Solar System” University of Arizona uanews.org  available online at
 “Especially prominent are the Nilae Fossae around the Isidis basin, but less distinct concentric graben and scarps are visible around the Argyre and Hellas basins.” BY THE VIKING ORBITER IMAGING TEAM “Deformational features” NASA SP-441
 “Introduction: The Margaritifer Sinus region of Mars preserves some of the highest valley network densities on the planet [1-4]. Two large northwest draining valley systems, Samara and Parana-Loire Valles, whose associated basins cover an area exceeding 540,000 km2, dominate regional drainage. These valley systems converge on Margaritifer Basin, a confluence plain shared with the Uzboi-Holden-Ladon-Margaritifer Valles meso-outflow system (UHLM) that drains northward from Argyre. Detailed geologic and morphometric mapping of the Samara and Parana-Loire valley systems confirms the timing of incisement and permits evaluation of possible mechanisms for valley evolution [2, 5-8].” J. A. Grant “Valley Evolution in Margaritifer Sinus, Mars” Available online at
 “features in Margaritifer Sinus. Four resurfacing events that deposited materials interpreted to be of mostly volcanic origin on the basis of wrinkle ridges and occasionally lobate morphology followed formation of these basins. The first three resurfacing events were
widespread and ended before evolution of the preserved valleys; the first two occurred during early Noachian heavy bombardment  and the second ended at an N5 age of 1400 (number of craters >5 km in diameter
per 1,000,000 km2). By contrast, the third resurfacing event began during the middle Noachian (N5 of 500) and ceased during the late Noachian (N5 of 300) coincident with waning highland volcanism . Formation of Samara and Parana-Loire Valles, the UHLM system, infilling of associated depositional sinks (e.g., Parana Basin at 12.50W, 22.50S), and initial collapse of Margaritifer Chaos all occurred from the late Noachian (N5 of 300) into the early Hesperian (N5 of 150). The last, more localized resurfacing event lasted into the early and middle Hesperian (N5 ages 200 to 70) and emplaced materials that embay valleys. Nearly all area surfaces have been subsequently modified to varying
degree by eolian activity.” Ibid. available online at
 “Model for Valley Evolution: A model for valley formation consistent with these results involves mostly localized ground-water discharge enabled by surface fed recharge. In this model, precipitation (rain or snow) would be largely relegated to subsurface entry by high
surface-infiltration capacities. Discharge at exposed relief would be controlled by occurrence of layers/ aquitards. Valley evolution would have continued until draw-down of the water table following cessation
of precipitation, thereby resulting in a strong sapping overprint.
Martian valley formation by this process may best explain observed morphometry. For example, the basin wide distribution of valleys (Fig. 1), low drainage density and ruggedness numbers, degree of integration,
and sediment volume in along-valley sinks may be difficult to accommodate in a hypothesis involving ground-water discharge in the absence of surface recharge. With surface-fed recharge, valley distribution would be controlled mostly by the occurrence of layers/
aquitards.” Ibid. Available online at
 “The crustal structure accounts for the elevation of the Martian northern lowlands, which controlled the northward flow of water early in Martian history, producing a network of valleys and outflow channels. The new gravity-field data suggest that the transport of water continued far into the northern plains. The gravity shows features interpreted as channels buried beneath the northern lowlands emanating from Valles Marineris and the Chryse and Kasei Valles outflow regions.” Goddard Space Flight Centre “View inside Mars reveals rapid cooling and buried channels” March 9 2000 available online at http://www.gsfc.nasa.gov/topstory/20000309mars.html
 “Geologic mapping in Margaritifer Sinus, Mars, defines a complex history of water transport, storage, and release that began in the late Noachian and persisted into at least the mid-Hesperian. Collection, transport, and discharge of the water from widely dispersed surfaces were accomplished by systems of differing character flanking opposite sides of the Chryse Trough. Drainage on the western side of the trough was accommodated by the segmented Uzboi-Ladon-Margaritifer mesoscale outflow system that heads in Argyre basin, drains approximately 9% of the Martian surface, and alternately incises and fills as it crosses ancient multi-ringed impact basins.” John A. Grant “DRAINAGE EVOLUTION IN MARGARITIFER SINUS, MARS” Paper No. 132-0 GSA Annual Meeting, November 5-8, 2001 Boston, Massachusetts http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_27669.htm
 Dave Williams “Parana Valles drainage system in Margaritifer Sinus, Mars” available online at
 “Using high-resolution topographic data from the Mars Orbiter laser
altimeter (MOLA) instrument on the Mars Global Surveyor mission
(Smith et al., 1999), we have gathered evidence for a major fluvial
resurfacing event in the Martian highlands. We completed detailed geomorphic mapping for the Margaritifer Sinus region (08–308S, 08–
308W), where resurfacing appears most evident. In addition, evidence
from adjacent areas suggests that this was not a localized event, but
one that affected at least 1 3 107 km2 (an area equivalent to the European continent) of the cratered uplands. The topographic information
allows for the first time a separation of younger, low-standing fluvially reworked terrains from older, high-standing erosional remnants. The newly acquired MOLA data also allow the volume of eroded material to be sensibly determined and minimum erosion rates to be estimated. The erosional episode was limited in time to no more than several hundred million years, and occurred ca. 4 Ga. The scale of the processes involved strongly suggests, but does not demonstrate uniquely,
that precipitation must have played a major role in landscape denudation
in this region of Mars.” Brian M. Hynek and Roger J. Phillips “Evidence for extensive denudation of the Martian highlands” available online at
 Formation processes of valley networks are still controversial; the
debate is largely focused on the relative roles of surface runoff and
groundwater processes. In the mapped region, the morphology of the
valleys and associated networks (v-shaped profile, sinuous, high density, and high valley order) and the observation that numerous valleys originate near the tops of crater rims or hilltops (Fig. 3) indicate that precipitation and surface runoff may have played a major role in their formation. Some valleys show morphologies more consistent with a groundwater-sapping origin (u-shaped profile, low density and order, and alcove-like terminations), suggesting that subsurface water was also important. Therefore, both precipitation and groundwater certainly contributed to degradation in the Margaritifer Sinus region, but the relative importance of each erosion mechanism is unclear. These results are consistent with previous work completed on the south-central part of our study area (Grant, 2000).” Ibid. available online at
 “There is evidence for a large paleolake in the region (Parana basin;
22.58S, 12.58W, area ;33 000 km2) (Goldspiel and Squyres, 1991). The
depression contains hummocky interior deposits with interspersed smooth terrain (Ni) that were emplaced contemporaneously with the extensive denudation and valley network formation. A large number of valley systems terminating at the proposed shoreline of Parana basin are believed to have been sources for the paleolake (Goldspiel and
Squyres, 1991). The unit HNl contains a hematite spectral signature
and is interpreted to be sedimentary layers deposited from large-scale
water interactions (Christensen et al., 2000).” Ibid. Available online at http://ltpwww.gsfc.nasa.gov/tharsis/hynek.erosion.pdf
 “J.A. Grant examined the valley networks in the Margaritifer Sinus region, the area on Mars where they are most concentrated, and concluded that they were indeed carved by "sapping" (tunneling by underground water flows) rather than surface runoff -- but also that the only way such a subsurface water supply could be adequately replenished was if "widespread precipitation" in the form of rain or snow occurred in the region and then seeped into Mars' porous ground.
B.M Hynek concluded from MGS' laser topography maps that the western Arabia Terra ("Arabia Highlands"), an area the size of Europe, was so eroded by surface rain that 3 million cubic km of its material was gradually washed into Mars' low-altitude northern plains.
K.P. Harrison and R.E. Grimm examined the fact that the areas on Mars where valley networks seem to be most concentrated are also those where MGS' magnetic sensors -- to everyone's surprise -- found local magnetic fields which seem to be areas where crustal iron minerals have been permanently magnetized by Mars' long-vanished early magnetic field.
Since this most easily occurs when molten rock is exposed to a magnetic field at the same time that it is rapidly cooled into solid form, the obvious possibility is that rising flows of underground magma may have collided in these areas with large amounts of groundwater kilometers below the surface, providing a flow of geothermal hot springs for the valley networks, and also cooling the magma quickly enough to "freeze" a copy of Mars' magnetic field into the resulting solid rock before Mars' magnetic field could reverse polarity (which, like Earth's, it probably did every million years or less) and thus scramble the permanently recorded "fossil" field.
D.M. Nelson examined the highlands south of the Elysium Basin -- through which three especially big channels seem to have carried fluid for a long period -- and concluded that the area showed signs of having undergone repeated cycles of geological peace that would have allowed a local layer of ground ice to build up, and episodes of moderate volcanism just right to melt the accumulated ice and produce large water flows into Elysium.”Bruce Moomaw “Mars: A World of Varied Catastrophes” MARSDAILY May 1, 2001 available online athttp://www.spacedaily.com/news/lunarplanet-2001-01a2.html
 “Valley networks were examined in detail (25) in Margaritifer Sinus, a region on the flank of the Arabia bulge and in the Tharsis
trough (Fig. 3B). Most formed on regions of relatively high topographic gradient on the flanks of the trough. The majority (;85%) of
observed valley networks here likely formed in Late Noachian time, between ;4.3 to 3.85 billion years ago (Ga) and ;3.8 to 3.50 Ga
(26), although the possibility exists that earlier valley networks in this region were destroyed by a high impact flux or alternative
erosion mechanisms. Because many of these valley network orientations are controlled by Tharsis-induced slopes, the Tharsis load must
be largely Noachian in age, which is consistent with inferences made earlier. Superposition and sequence relationships indicate that
the valley networks whose azimuths are not explained by the model are nevertheless contemporaneous with the Tharsis-controlled valley networks (27). The formation of valley networks in Margaritifer Sinus is intimately associated with a Late Noachian, large-scale erosion event on the flanks of the Tharsis trough that stripped at least 1.5 3 106 km3 of
material from this area, leaving behind numerous mesas of Early and Middle Noachian terrain (25).” Roger J. Phillips et al “Ancient Geodynamics and Global-Scale Hydrology on Mars” www.sciencemag.org SCIENCE VOL 291 30 MARCH 2001 available online at
 Goddard Space Flight Center Educational Programs  image of Valles Marineris available online at http://education.gsfc.nasa.gov/experimental/all98invProject.Site/Pages/Vallis.Marineris.html
 Image of Valles Marineris
 “Figure 1 shows two recent magnetic maps of Mars derived using these techniques. The anomalies have a pattern strongly suggestive of faulting and perhaps offset along faults along a major tectonic structure. The Vallis Marineris on Mars is a series of large, fault-bounded canyons which have been compared with major rift structures on the Earth. The pattern in the magnetic maps, especially the abrupt truncation of the anomalies at the wall of the canyon, supports the idea that the Valles Marineris canyon is a tectonic graben. The maps also suggest that highly magnetic source rocks exist at the intersection of Coprates and Capri Chasmata, on the northeast corner of the canyons, and there is a good possibility that these magnetic rocks may be exposed along the fault wall.” Herbert Frey Geodynamics 2001 The Year in Review available online at
 M.E. Purucker et al “Interpretation of a magnetic map of the Valles Marineris region, Mars” available online at
 “Paleolake deposits have been mapped in Central
Valles Marineris since Mariner 9 and Viking
(McCauley, 1978; Nedell et al., 1988;Witbeck et al., 1991). Accordingly, the region has been proposed as a priority target for landed payloads intended to detect diagnostic mineral evidence of a permanent lake environment, and, especially, biogenic signatures that could have survived from such promising candidate Martian habitats. (eg, Murray, et al, 1996; Yen, et al, 1999, Murray, et al, 1999). Just-released MOLA data strongly buttress the hydrological case for longduration ice-covered lakes there during Hesperian times at least.” Bruce Murray  “PALEOLAKE DEPOSITS IN CENTRAL VALLES MARINERIS: A UNIQUE OPPORTUNITY FOR 2001” Second Mars Surveyor landing site Workshop available online at
 “Carr (1996) suggested that ground water flowed from the Tharsis uplands into the deep canyons of Valles Marineris before debouching onto Chryse Planitia in the northern plains. Such a flow may have persisted for billions of years, and is generally inferred to have maintained deep lakes beneath which lacustrine sediments accumulated. Remnants of these Hesperian Age lake deposits survive today as conspicuous layered
strata in Central Valles Marineris. Just published MOLA data (Smith, et al, 1999) confirm in detail this topographic trend and, most importantly, prove that deep, permanent lakes did indeed exist, especially in Central and Western Valles Marineris. Because the canyons in the Valles Marineris are deeper than the probable ground water table at that period, large portions of the canyons would have filled with water and formed ice-covered lakes.” Ibid. available online at
 Valles Marineris Outflow Site (MER-A) http://marsoweb.nas.nasa.gov/landingsites/mer2003/topsites/VMout/zoom.html
 “The channel is unusual because it appears to represent a single outflow initiated by a large impact. This impact could have excavated materials from the Martian crust from depths of several kilometers, apparently “tapping” the aquifer system leading to catastrophic
flooding to form the channel. Ejecta from the Noachian impact crater [6, 7] is preserved NW-W and SE from the source area. The width of Shalbatana Vallis near its source is about 50 km and then it continues 500 km NE as a sinuous, narrow channel of nearly constant width (10 -20 km cross) and depth (~2 km). The channel then becomes wider (40-50 km), bifurcates, and enters Simud Vallis .” Ronald Greeley and Ruslan Kuzmin “SHALBATANA VALLIS: A POTENTIAL SITE FOR ANCIENT GROUND WATER” MSL99 Workshop available online at
 “DISCUSSION The irregular shape and lack of significant downrange ejecta that surrounds Orcus Patera do not help support an impact origin; it is important to note that Orcus Patera and Schiller are very similar in shape, but the origin of Schiller is also poorly understood at present. The average flank slope ETF value of –0.30 found for Orcus Patera is only barely within the –0.30 to –2.33 range for ETF exponents that were found for other Martian impact craters . Cavity-wall slopes range from 4.33 to 9.65º and are more gradual than expected for degraded Martian impact craters. The floor of Orcus Patera is relatively flat, though this appears to be the result of post-formation lava flooding; the feature’s cross sectional geometry is thus not typical of an impact crater of this size. MOLA colorstretched topographic grids around the depression reveal a shape that could be interpreted as the remnants of a butterfly ejecta pattern commonly emplaced by elliptical impact craters. However, taken together, these data provide insufficient grounds for interpreting Orcus Patera as an impact basin. Unfortunately, Orcus Patera’s elliptical shape, interior resurfacing, and floor topography also fail to provide enough strong support for a solely volcanic origin. For instance, the plan view shape of the basin is similar to that of Long Valley caldera, one of the largest elongate calderas on Earth. Orcus Patera’s depth below the surrounding plains and truncated asymmetric flanks, however, are similar to what is observed for small volcanic edifices in the Tharsis region on Mars, where subsequent deposits have flooded onto the flanks. Finally, if Orcus Patera is volcanic in origin, the difference in absolute age for Orcus Patera’s interior and exterior deposits  (volcanic infilling in the interior is younger than the surrounding flanks) suggests that the feature had a prolonged volcanic history and multiple episodes of flooding. Further investigation of relative and absolute ages for smaller distinct units within this region is necessary to identify whether volcanism played a key role in the origin of Orcus Patera or simply modified it subsequent to formation.” D.A. van der Kolk et al “ORCUS PATERA, MARS: IMPACT CRATER OR VOLCANIC CALDERA?” Lunar and Planetary Science XXXII (2001) 1085.pdf
 “Summary. Geologic mapping of southern Chryse Planitia and the Xanthe Terra outflow channels has revealed a sequence of fluvial events which contributed sediment to the Mars Pathfinder landing site (MPLS). Three major outflow episodes are recognized: (1) broad sheetwash across Xanthe Terra during the Early Hesperian period, (2) Early to Late Hesperian channel formation of Shalbatana, Ravi, Simud, Tiu, and Ares Valles, and (3) subsequent flooding which deepened the channels to their current morphologies throughout the Late Hesperian. Materials from the most recent flooding, from Simud and Tiu Valles, and (to a lesser extent) materials from Ares Vallis, contributed the greatest amount of sediment to MPLS.” D.M. Nelson, R. Greeley “XANTHE TERRA OUTFLOW CHANNEL GEOLOGY AT THE MARS PATHFINDER LANDING SITE” Lunar and Planetary Science XXIX 1158.pdf
 “Following sheetwash, Mawrth Vallis was formed, possibly resulting from the discharge of floods from Margaritifer and Iani Chaos. A broad area of subdued terrain east of Ares Vallis indicates buried and embayed
craters to the south of Mawrth Vallis. Floods could have passed over this surface before excavating Mawrth, then drained downslope into Acidalia Planitia. Alternatively, the subdued area could be a spill zone
formed during the early excavation of Ares Vallis. Channelization continued in the Late Hesperian with the development of Shalbatana, Ravi, Simud, Tiu, and Ares Valles. Shalbatana Vallis possibly formed by
subterranean discharge from Ganges Chasmata , and Ravi was excavated by flooding from Aromatum Chaos. Simud and Tiu Valles then developed by floods from Hydraotes and Hydaspis Chaos, and Ares Vallis developed by flooding from Iani Chaos. Cross-cutting relationships in Ares and Tiu Valles suggest that multiple floods occurred within these channels.” Ibid. http://mars.jpl.nasa.gov/MPF/science/lpsc98/1158.pdf
 “Surfaces on Mars that date to the period of heavy bombardment are different from the Moon in that processes other than cratering have modified the surface both during and, to a lesser extent, subsequent to the cratering epoch. This image shows an area in Mars in the region "Terra Tyrrhena" at about 285 degrees west longitude and 5 degrees south latitude and shows an area about 500x500 kilometers. It is fairly typical of areas of the heavily cratered terrain that have been extensively modified during and immediately after the period of heavy bombardment. Most of the large craters have very smooth floors.” A.D. Howard “Features of Martian Cratered Terrain” GEOMORPHOLOGY HOME PAGE University of Virginia available online at
 “Scarp retreat: Large areas of Mars downslope of the present-day dichotomy scarp are littered with remnant knobs, and distinctive valleys – the fretted terrains, eat back into the scarp. Collectively they
appear to represent ~ 1000 km of scarp retreat in a planet-encircling belt. Profile analysis suggests that the missing volume represents a wedge 4 km thick at the present day scarp and tapering to zero over the 1000km width of the belt of fretted and knobbed terrain. Extending this in a girdle planetwide, we come up with ~5 x 107 km3 –the volume of the sediments.
Scenario: As the dichotomy collapsed, the slurries would have poured into the northern lowlands, filling and covering pre-existing cratered terrain and emplacing thick deposits on a very rapid timescale. Outgassing from trapped volatile CO2 would produce mud volcanoes [8, 9] and phreatic cones  as CO2 escaped to surface and blasted loose debris upwards. The northern plains would have been an extensive,
mobile “sea” of fluidised debris – a “Mud Ocean” . Its surface would have been wreathed in clouds of escaping CO2 from fumaroles, fissures, and vents. The margin of the Mud Ocean would have been like the
flow front of an aa lava – advancing in a bulldozer-like carpet, burying and engulfing the surrounding terrain, and steaming from the escape of CO2. The speed of advance would have been, like lava flows, very
variable and a function of fluid supply behind the flow front. Long stillstands and episodes of slow creep would alternate with short intervals of hundreds of metres per day, or more.” N. Hoffman et al “EMPLACEMENT OF A DEBRIS OCEAN ON MARS BY REGIONAL-SCALE COLLAPSE AND FLOW AT THE CRUSTAL DICHOTOMY” Lunar and Planetary Science XXXII (2001) 1584.pdf
 K. F. Sprenke and L. L. Baker “POLAR WANDERING ON MARS?” Lunar and Planetary Science XXXI 1930.pdf
 “Syria Planum: Syria Planum is the site of long-lived (Noachian to Late Hesperian) magmatic-driven activity with distinct episodes of intensive early magmatic/tectonic activity that declined in tectonic
intensity by an order of magnitude from the Late Noachian to Late Hesperian [2,25], transitioning mainly into a dominantly volcanic setting during the Late Hesperian . Some of the dominant
characteristics of Syria include: (1) local and regional uplifts, (2) extensional and contractional tectonism, (3) dike emplacement, including the formation of Late Hesperian and possibly younger pit crater chains, (4) volcanism including the formation of shield fields  and the emplacement of voluminous sheet lavas that may range in relative age from the Late Noachian to the Late Hesperian ,”
 “Preliminary results indicate that Syria had a greater impact on the evolution of the Tharsis magmatic complex than Alba.” R. C. Anderson et al “COMPARATIVE INVESTIGATION OF THE GEOLOGICAL HISTORIES AMONG ALBA PATERA AND SYRIA PLANUM, MARS” Lunar and Planetary Science XXXIII (2002) 1811.pdf
 “The Hellas Basin is an ancient impact structure on Mars, approximately 3000 km long by 1500 km wide” J. Richardon “Isostacy in the Hellas Basin on Mars” available online at http://www.lpl.arizona.edu/~jrich/work/hellasslides.pdf
 N. Hoffman “Water on mars? Who are they trying to kid?” School of Earth Sciences University of Melbourne available online at
 “Glacial History: There are a variety of distinct landforms on Mars that are interpreted to be associated with the presence of ground ice/permafrost [9-11]. Today, the only visible surface ice occurs at the permanent polar caps, although water ice is physically stable poleward of 45° N and S latitude. Some investigators have suggested that the ice cover was once more extensive, particularly in the southern hemisphere. Kargel  mapped the occurrence of a suite of landforms in Hellas that may have had a common glacial origin. These features, which he interpreted to be glacial scour marks, moraines, drumlins, and eskers, are shown in Figure 1.” B. J. Thomson and J. W. Head “THE ROLE OF WATER/ICE IN THE RESURFACING HISTORY OF HELLAS BASIN” Fifth International Conference on Mars 6200.pdf http://www.lpi.usra.edu/meetings/5thMars99/pdf/6200.pdf
 “It remains unclear whether the grooved terrain, if it is indeed glacial in origin, is indicative of a local, isolated glacier or whether it was part of a more extensive ice sheet in the southern hemisphere.” Ibid. available online at http://www.lpi.usra.edu/meetings/5thMars99/pdf/6200.pdf
 “Channel and Lacustrine Deposits: Northwards of the proposed area of maximum glacial extent there is a region interpreted to be influenced by glacio-lacustrine processes. Kargel  mapped a portion of the shoreline of a possible proglacial lake. The MOLA data reveal that this mapped shoreline lies almost entirely at the -6000 m elevation level. Possible sources of input to this lake is water derived from retreating glaciers as well as outflow channels which empty to Hellas from the east. The esker field, in which the long axis of the features in oriented north-south, may represent subglacial flow of water into a proglacial lake. The eastern channels also might have contributed to this lake. These small channels resemble other outflow channels
in gross morphology, but are greatly reduced in size. Interestingly, channel cutting terminates abruptly on the basin floor in a manner that is very similar to the abrupt cessation of the circum-Chryse outflow channels. The paucity of tributaries along the length of these Hellas channels suggests a localized source region, possibly due to volcano/ground ice interactions.” Ibid. available online at http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6200.pdf
 “Glacial Hypothesis: There are a variety of distinct landforms on Mars that have been attributed to the presence of ground ice/permafrost [7-9]. Today, although water ice is physically stable poleward of 45° N and S latitude, the only visible surface ice occurs at the permanent polar caps. Some investigators have suggested that the polar ice cover was once more extensive earlier in Mars’s history [e.g. 10-12]. Kargel and Strom  mapped the occurrence of a suite of landforms in Hellas which they believed share a common glacial origin. These features, which include glacial scour marks, moraines, drumlins, and eskers, are proglacial lacustrine deposits, are shown in Figure 1. The proposed age of the latest episode of glaciation is middle Amazonian. Three predictions of the glacial hypothesis that we have investigated with MOLA data are 1) glacial scouring on the south rim, 2) a shoreline from a pro-glacial lake in the north, and 3) a suite of glacial depositional landforms on the basin floor.” Bradley J. Thomson and James W. Head “HELLAS BASIN, MARS: EXAMINATION OF A GLACIAL HYPOTHEISIS WITH MOLA TOPOGRAPHY” 32-th Vernadsky-Brown Microsymposium / Abstracts available online at http://www.geokhi.ru/~planetology/Abstracts/Thompson%20et%20al.pdf
 Jakupova A. E. et al “PREPARATION OF AN ATLAS OF THE CRATERING OF MARS” 38th Vernadsky/Brown Microsymposium on Comparative Planetology available online at
 “In this topographic portrayal of Mars, above, the northern lowlands are occupied by an ocean (blue) whose shoreline is placed at the position of Contact 2, the line that Parker and co-workers interpreted as an ancient shoreline. Thus, this view shows Mars as it might have looked mid-way through its history according to the oceans hypothesis. The Tharsis region, with numerous very large shield volcanoes is seen in the central part of the globe. In the upper right, many channels flow into the northern lowlands at Chryse Planitia.” NASA Mars Global Surveyor Project; MOLA Team “Possible configuration of ancient oceans on Mars: Topographic portrayal of the surface of Mars derived from Mars Orbiter Laser Altimeter (MOLA) data” available online at
 See Figure 2 for shorelines and Figures 3 A to F for polygons and craters with ejecta lobes.
“Martian impact craters in the 2- to 50-kmdiameter range commonly have ejecta deposits with distinctive lobe and rampart morphology, interpreted to be due to the presence of groundwater or ground ice in the target area that mobilizes the ejecta material (22). Craters on Mars smaller than a few kilometers generally do not have unusual ejecta ramparts, and thus the onset diameter of ramparts may be an indication of the depth at which groundwater or ground ice is encountered during cavity excavation. On the basis of this concept, Kuzmin et al. (23) assessed the onset diameter globally. Using their map, we found a correlation between the lower range of onset diameters (,4 km) and the northern lowlands (Fig. 3B). The craters with the smallest diameters (,2 km) correlate with the position of the two large basins within the northern lowlands, a distribution consistent with an interpretation of groundwater or ground ice occurring preferentially near the surface in the northern lowlands and particularly in the interiors of the two basins (7, 8).” James W. Head III et al. “Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data” 10 DECEMBER 1999 VOL 286 SCIENCE www.sciencemag.org available online at
 “An initial step towards identifying the mechanism of formation
of Amazonis Planitia is to compare its topographic properties to other smooth regions with potentially analogous origins. Shown in Figure 4 are pro_les of elevation collected by various altimeters over smooth surfaces from a variety of solar system bodies. At the top is MOLA Pass
31 over Amazonis Planitia, where the anomalously smooth region is observed to extend over 600 km, approximately centered in the plot (vertical point-to-point accuracy _z _ 0:4 m, horizontal resolution _x _ 0:3 km). Below is a Clementine pro_le of the Moon's Oceanus Procellarum (_z _ 40 m, _x _ 2 km for 1 Hz data and _ 0:2 km for 8 Hz data)
[Smith et al., 1997], Magellan radar altimetry over Niobe Planitia (_z _ 4 m, _x _ 10 km) [Ford and Pettengill, 1992], Shuttle Laser Altimeter data collected over the Sahara desert (_z _ 1:5 m, _x _ 0:7 km) [Garvin et al., 1997], and shiptracks of Seabeam 2200 bathymetry over the south
Atlantic abyssal plains (_z _ 2 m, _x _ 0:1 km) [Neumann et al., 1996]. The last two pro_les were extracted from the GTOPO data set (highly variable _z _ 20 m, _x _ 0:1 km) [Gesch and Larson, 1996], _rst over the Great Plains in the U.S., and second over the Indo-Gangedic Plains across over the Tibetan Plateau, down across the Tarim Basin and continuing northwards. Oceanus Procellarum consists of lava flows that have been broadly tilted by subsidence and locally steepened by tectonic deformation (wrinkle ridges); their small-scale roughness is dominated by impact regolith formation processes. Niobe Planitia on Venus consists of vast lava plains similarly tilted and steepened but not influenced
by regolith formation. Comparison of these surfaces reveals that of these lowest, smoothest regions observed in the solar system, Amazonis Planitia closely resembles in its smoothness only the heavily sedimented surfaces on the Earth, i.e. oceanic abyssal plains and basins _lled by fluvial deposition processes. It is noteworthy that volcanically resurfaced terrain is markedly rougher on the Moon, on Venus, and on
Mars, than the peculiar Amazonis deposits. Saharan sand sheets are rougher by a factor of about three. Other regions in the Martian northern hemisphere that exhibit evidence of dust deposition are rougher than Amazonis as well.” Oded Aharonson, Maria T. Zuber and Gregory A. Neumann “Mars: Northern hemisphere slopes
and slope distributions” GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 24, PAGES 4413-4416, DECEMBER 15, 1998 available online at
 “RATIONALE: The debouche of Ma'adim Vallis in the Elysium Basin generated a transitional transported sediment structure, which planimetric shape is controlled by the enclosing topography of a deep re-entrant gulf of the Basin into the highland. We defined it as an estuarine delta. The location and the importance of this estuarine delta is supported by the theoretical model of graded profile constructed for Ma'adim Vallis , and by two approaches: (i) the reconstruction of Ma'adim Vallis downstream course from Gusev to Elysium Basin (figure 1), and (ii) the survey of the sediment deposit in the alleged estuary. The longitudinal graded profile of Ma'adim Vallis finds its base-level in the Elysium Basin, at a -1000 m elevation , which is in agreement with the observed Basin shoreline . This model is supported by observational evidence of flow between the northern rim of Gusev crater, and the Elysium Basin shoreline. This downstream course of Ma'adim Vallis can be divided into three hydro geologic regions. Cabrol et al “Duration of the Ma'adim Vallis/Gusev crater hydrogeologic system, Mars” Icarus 133, 98-108 .
 “flowing around the aureole. These three barriers (degraded Noachian crater rim, proto- Olympus Mons flow unit, and Olympus Mons aureole) caused subsequent lava flows and outflow channel effluents, primarily from the Elysium region to the west, to pond on the floor of Amazonis Planitia, preferentially smoothing the terrain there. Mars Orbiter
Camera (MOC) images substantiate that at least two very fluid lava flows alternated with fluvial episodes from Elysium Planitia, flowing through Marte Valles onto the floor of the Amazonis Planitia basin. Within Amazonis Planitia, MOC images show flow-like textures heavily mantled by sediments, and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris. These data thus suggest that the unique smoothness of Amazonis Planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin. Crater counts suggest that the most recent resurfacing may have occurred in the latest Amazonian Period, in the last 1% of the history of Mars.” Elizabeth R. Fuller and James W. Head III “Amazonis Planitia: The role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on Mars” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. E10, 5081, doi:10.1029/2002JE001842, 2002 available online at
 “Introduction: This study seeks to understand origin of the equatorial layered deposits (ELDs), including the Medusae Fossae Formation (MFF) the filled craters of Elysium and Arabia Planitiae (
Gusev and Henry Craters). Several origin hypotheses have been proposed for the MFF [c.f. summary in most involving a pyroclastic origin but one proposing formation at the poles . Previous work using MOLA to test the polar formation theory found there are both similarities and significant differences between the equatorial and polar layered deposits, concluded that the MFF may be volatile rich, but not form at the poles . Another MOLA-based study similarly found that the deposits were not polar origin, and instead concluded that they were most consistent with a welded ashfall tuff .  further showed that the ELDs could not be evidence of polar wander on the basis of the time scales necessary for polar wander to have occurred. Morphological evidence also indicates that while there are similarities between the poles and the ELDs, including extensive layering at multiple scales, unusual smoothness at several scales [see also discussion in steep slopes (~1-6° in the MFF, ~1-10° at the poles), and distal thinning of the materials, there are fundamental differences, notably the lateral extent the ELDs: the MFF itself reaches across 90 longitude (Figure 1), and filled craters are present around the globe. If the ELDs did form by mechanism similar to that of the poles, what were sources of the volatiles, and how did they reach equator?
Volatile sources: There are three Amazonian-aged volatile sources in the equatorial region: degassing from nearby volcanism, Elysium-region catastrophic outflow, and polar material migration during periods
high obliquity. 1) Degassing: The Tharsis Montes, Olympus Mons, and Elysium Mons were all active during the Amazonian.  showed that these eruptions were most likely plinian, with extensive magmatic degassing releasing CO2 and H2O. Regional outflow:  and  have shown that waterrich debris flowed down the northwestern flanks Elysium Mons in the mid-late Amazonian. Additionally, in the late Amazonian there was repeated catastrophic release of water in Elysium Planitia, through Marte Vallis, debouching into Amazonis Planitia . 3) Migration of polar materials: periods of maximum obliquity, the poles receive more insolation than the equator. As the poles warm, ice becomes unstable and is forced to migrate to a new cold trap (see below) .” E. R. Fuller and J. W. Head, III “PROPOSING A HIGH VOLATILE CONTENT IN THE EQUATORIAL LAYERED DEPOSITS INCLUDING THE MEDUSAE FOSSAE FORMATION, MARS” Microsymposium 36, MS022, 2002 Available online at
 “Tectonics: In the highlands of Amenthes-northern Terra Cimmeria and northern Arabia Terra, lobate scarps are found between approximately 200 to 600 km south of the dichotomy boundary. These lobate scarps, interpreted to be the surface expression of thrust faults, are oriented roughly parallel to the dichotomy boundary (Figure 1). The proximity and parallel orientation of thrust faults to the dichotomy boundary suggests that compressional deformation was involved in its formation
. Extension along the boundary is thought to have occurred during the Late Noachian to Early Hesperian . Thrust faulting of the highlands near the boundary appears to have occurred during roughly the same period [2, 4]. Thus the fractures and thrust faults may reflect a tectonic event that was associated with the dichotomy boundary (Figure 1). The deformation along the boundary suggests that the dichotomy formed in the Late Noachian to Early Hesperian [2, 3]. If the dichotomy formed earlier, this deformational event may have been responsible for shaping the present-day dichotomy boundary in the eastern hemisphere.”
T. R. Watters “THE TECTONICS AND TOPOGRAPHY OF THE DICHOTOMY BOUNDARY IN THE EASTERN HEMISPHERE OF MARS” Lunar and Planetary Science XXXIII (2002) 1692.pdf
 “Distinctions include: (1) magmatic-driven activity from at least the
Early Hesperian extending into the Amazonian [1,7-8]” R. C. Anderson et al. “COMPARATIVE INVESTIGATION OF THE GEOLOGICAL HISTORIES AMONG ALBA PATERA AND SYRIA PLANUM, MARS” Lunar and Planetary Science XXXIII (2002) 1811.pdf
 “4. Conclusions
 Detrended MOLA altimetry data have provided a new picture of the Martian northern lowland basin topography, morphology, evolution, and relation to the history of Mars. We interpret our results to indicate that the northern lowlands are underlain by a regional unit containing a basin-wide system of subparallel wrinkle ridges and arches. This unit is laterally contiguous with Hesperian-aged ridged plains in the southern uplands and contains highly modified craters, the number of which suggests an Early Hesperian age. The orientation and location of the
wrinkle ridges in the North Polar Basin completes a global circum-
Tharsis ridge system forming a band approximately 7000 km wide and extending over the whole circum-Tharsis region. Several subareas of the northern lowlands show individual patterns (e.g., basin-like areas of Isidis and Utopia). The present spacing and height of wrinkle ridges and geometry of buried craters in the northern lowlands suggest that the Late Hesperian Vastitas Borealis Formation is a sedimentary unit superposed on Hr (regional plains). Hesperian-aged channels entering Chryse Planitia are controlled by the orientation and topography of wrinkle ridges deep into the basin, indicating that wrinkle ridges had largely formed by Late Hesperian. These channels are among the strongest
candidates for providing the material of the Vastitas Borealis Formation. Amazonian-aged smooth plains units of volcanic origin, particularly in Amazonis Planitia, further bury and obscure the underlying wrinkle ridges and the Vastitas Borealis Formation.  Recognition of these units and their stratigraphic relationships provides a new perspective on the history of the northern lowlands (Figure 17). In this scenario, in the Early Hesperian the majority of the northern lowlands was filled with volcanic plains similar to those presently exposed in the southern uplands (Hr). As with those deposits in the southern uplands, evidence for volcanic vents was scant or subdued in topography. The Hesperian-aged plains in the northern lowlands were pervasively deformed soon thereafter by Tharsis-circumferential and basin-related wrinkle ridges. Circum-Chryse outflow
channels formed in the Late Hesperian following courses largely controlled by wrinkle ridge orientation and height and deposited material in the basin to form a major contribution to the Vastitas Borealis Formation.
 Widespread emplacement of the Hesperian-aged ridged
plains of apparent volcanic origin is interpreted to mean that the
volcanic phase represented by this unit was global in nature and resurfaced the northern lowlands, in addition to the _10% of the
planet previously known, for a total resurfacing of about 30% of
Mars. This remarkable event increases by a factor of 2 the amount
of volatiles that might have been degassed into the atmosphere
during this time period of peak volcanic flux.” James W. Head III et al. “Northern lowlands of Mars: Evidence for widespread volcanic flooding and tectonic deformation in the Hesperian Period” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. 0, 10.1029/2000JE001445, 2002 available online at
 “ We analyze the fate of the Hesperian-aged outflow channel effluents emplaced into the northern lowlands of Mars. We have modeled the evolution of these effluents under the assumption that they were emplaced under a range of atmospheric conditions comparable to those of today and thought to have prevailed in the Hesperian. Under these conditions we find that the evolution of the sediment-loaded water after it left the channels includes three phases. Phase 1: Emplacement and intensive cooling: Violent emplacement of water followed by a short period of intensive evaporation from the surface and near-surface layer, and intensive convection. During this phase the water maintained and redistributed its large suspended sediment load. Water vapor strongly influenced the climate, at least for a geologically short time. When the temperature of the water reached the temperature of the maximum density or the freezing point, boiling and intensive convection ceased and the water deposited the sediments. Phase 2: Freezing solid: Geologically rapid freezing of the water body accompanied by weak convective water movement occurred over a period of the order of _104 years. Phase 3: Sublimation and loss: This period involved sublimation of the ice and lasted longer than the freezing phase. The rate and latitudinal dependence of the sublimation, as well as the location of water vapor condensation, crucially depend on the planetary obliquity, climate, and sedimentary veneering of the ice. Phase 3 would have been very short geologically (_105–106 years) if an insulating sedimentary layer did not build up rapidly. If such an insulating layer did form rapidly, sublimation could cease and residual ice hundreds of meters thick could remain below the surface today.” Mikhail A. Kreslavsky and James W. Head “Fate of outflow channel effluents in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. E12, 5121, doi:10.1029/2001JE001831, 2002 available online at
 “Resurfacing: We suggest that the latest resurfacing of the northern plains did not occur by sedimentation within an ocean or by widespread volcanism, but rather by the latest stages of long-term periglacial and thermokarst modification, with progressively reduced intensity occurring during the Hesperian through Early Amazonian. This activity obliterated or heavily modified earlier landforms, resulting in huge collapse structures, ghost craters, valley networks, highland/lowland fretted and knobby terrains, polar cavi terrains, and lowland thumbprint terrains. Such resurfacing likely involves erosion, ductile deformation, collapse, and effusive and violent eruptions of volatile charged material. The elevation dependence of the reworking may be related to gradual lowering of the threshold for near-surface volatile activity, as governed by the composition and distribution of subsurface volatiles and by the geothermal gradient. The difficulties to making Mars warm in the past and the lack of significant chemical weathering on Mars  seem to preclude substantial liquid water at the surface in the form of long-lived fluvial, lacustrine, and wet-based glacial activity. Instead, northern plains resurfacing may result mainly from the subsurface activities of both H2O and CO2 (CO2 being more volatile), as well as from local discharges of sediment enriched with these volatiles.”
K. L. Tanaka et al “RESURFACING OF THE NORTHERN PLAINS OF MARS BY SHALLOW SUBSURFACE, VOLATILEDRIVEN ACTIVITY” Lunar and Planetary Science XXXIII (2002) 1406.pdf
 “CO2 and Warm H2O Models: The simplest and most self-consistent model for the morphologies we see in and Athabasca Vallis and nearby “flood” valleys is that a volatile-rich debris flow was deposited and sculptured by roller vortices to produce the flow parallel ridges which were impregnated with the flow volatiles (Figure 3a). Given likely flow velocities, thicknesses, and rheology, roller vortices actually are only stable for debris flows and density flows (and not for aqueous floods or lava flows) . In the immediate aftermath of the flow, escape of highly volatile fluids from the ridges generated longitudinal chains of phreatic cones in a cryovolcanic process (Figure 3b). The most reasonable explanations for the Athabasca Vallis and its ridges of cones appears to be debris flows charged with warm water and/or CO2 gas-. Implications For Local And Regional Geology:
Whilst Athabasca Vallis is currently targeted as a MER 2003 backup candidate landing site, due to the evidence for recent outburst floods, the terrain does not require aqueous action. Instead, massive CO2-rich
gas-supported density flows may have resulted from outburst of subsurface liquid CO2 reservoirs rather than liquid water reservoirs.”
Nick Hoffman and Ken Tanaka “CO-EXISTING “FLOOD” AND “VOLCANIC” MORPHOLOGIES IN ELYSIUM AS EVIDENCE FOR
COLD CO2 OR WARM H2O OUTBURSTS” Lunar and Planetary Science XXXIII (2002) 1505.pdf
 “Fluvial geomorphology. The fluvial nature of the Marte Vallis outflow channel appears to be confirmed by MOC images  that show streamlined islands of several hundred meters to a couple of kilometers across, longitudinal grooves ten's of meters wide, and multi-level terraces on channel islands and margins. In conjunction with the anastomosing plan form of the channels, these features suggest channel formation by a high volume of low viscosity fluid that we hypothesize was sediment-laden water. Similar features also appear in MOC images to the north and west of the Elysium Basin, indicating the presence of some channels more substantial than previously supposed.” D. M. Burr et al “RECENT FLUVIAL ACTIVITY IN AND NEAR MARTE VALLIS, MARS” Lunar and Planetary Science XXXI 1951.pdf
 See images in
 “Discussion: MOC images have not shown many smaller networks as would be expected from precipitation. Malin and Carr  have suggested that the global lack of such dendritic channels may be due to modification by eolian and mass-wasting processes. However, the lava and channel
morphologies of the Elysium Basin region appear pristine. The dendritic channels, then, are likely absent from MOC images of the Elysium Basin because they did not form there. In addition, the anastomosing form of the channels suggests formation by exceptionally large flow. Thus, we believe that the MOC data fails to support the idea that the channel flood water derived from precipitation.” D. M. Burr “RECENT FLUVIAL ACTIVITY IN AND NEAR MARTE VALLIS, MARS” Lunar and Planetary Science XXXI 1951.pdf
 “Secondary geomorphic evidence: rootless cones. Rootless cones are seen throughout Athabasca Valles and the unnamed northern channel system, as well as in Amazonis Planitia, into which the Marte Vallis debouches . Rootless cones form when lava flows over and intimately mixes with wet substrate, volatilizing the water which then erupts up through the overlying lava flow . Rootless cone fields within
the channels, but not on the surrounding terrain, suggest that the water for their formation was emplaced by aqueous flow within the channels.”
D. M. Burr et al “EXTENSIVE AQUEOUS FLOODING FROM THE CERBERUS FOSSAE, MARS, AND ITS IMPLICATIONS FOR THE MARTIAN HYDROSPHERE” Lunar and Planetary Science XXXIII (2002) 1047.pdf
 “Source of the sediment: The sediment deposited in the streamlined forms was in transport by the floodwater. The floodwaters would have been carrying material entrained from the Martian surface during
the carving of Athabasca Vallis. Because they emanated from the Cerberus Fossae, the floodwaters may also have been carrying sediment from within the Fossae. Since the Fossae were a source for both water and lava, this sediment may have been hydrothermally altered. Athabasca Vallis was a candidate landing site for the Mars Exploration Rovers. If future landed missions target Athabasca Vallis, they may be able to collect sediment samples from the streamlined forms of such subsurface material.” D. M. Burr “TEMPORARY PONDING OF FLOODWATER IN ATHABASCA VALLIS, MARS” Lunar and Planetary Science XXXIV (2003) 1066.pdf
 “ The Cerberus Fossae fissures (Figure 1C) have very sharp edges and steep slopes (>80° indicated by shadows and viewing geometry in M04-03770) and cut sparsely-cratered plains (e.g., M07-03839). Thus, although their structural trend is also observed in remnant ancient highland terrain [Tanaka et al., 1992], we deduce the fissures to have been recently reactivated. That they appear to have been the source, not only of recent lava flows, but also of recent voluminous aqueous flooding, supports a causative relationship between the two types of flows, such as a scenario in which rising dikes melt ground ice [e.g., McKenzie and Nimmo, 1999] and open pathways to the surface. By analogy, the easternmost Cerberus Fossae could have been the main source for the larger aqueous floods down Marte Vallis [Tanaka et al., 1992], although geomorphic and topographic evidence may now be largely buried beneath Cerberus Plains lavas. Burr, D. M “4. Source of the Flood Water” GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 1, 10.1029/2001GL013345, 2002
 “Note the number of channels in this image. In places, these features look a lot like lunar sinuous rilles. They are all large flat-bottomed valleys. They begin abruptly in broad depressions. And their sources seem to form a ring centered on Elysium Mons. Like sinuous rilles on the Moon, these valleys might be lava channels. However, water is a more likely cause for their formation. Specifically, ground ice appears to have been widespread in the Elysium region. Such ice is easily melted near hot magmas. Thus, melt water provides a ready source for erosion in the Elysium region. Further, the loss of a lot of ground ice can cause collapse depressions near the channel sources.” S. De Silva “Elysium Mons” University of South Dakota available online at
 Mars Odyssey and MGS Mars Orbital Laser Altimeter (MOLA) Science teams “Mars Odyssey Orbiter Watches a Frosty Mars”  available online at
 “Due to the presence of two distinct phases of volcanism of such differing characteristics, it is proposed that these phases were separated by a period of repose. During this time the magma chamber, which had supplied the Elysium Mons vent, cooled sufficiently to alter the regional stress fields and produce tectonic activity observed in the Elysium Mons area e.g. arcuate graben. It is suggested that the chamber cooled sufficiently to act as a regional “plug” thus preventing
magma from the second phase of volcanism following the same course to the surface as that of the first phase. A repose period of 10 Ma has been estimated as a period of time sufficient to allow a magma chamber of 1100 km.” S.P. Bowling “Modelling the Effusion Rates and Activity Phases of the Elysium Volcanics” Lunar and Planetary Science XXX 1185.pdf
 “The whole of north Terra Meridiani (centered at lat. 0°, long. 0°) contains an unusual and enigmatic terrain unit. On the equatorial geologic maps of Mars, this highland area was mapped as being surfaced by two units of Noachian age: a subdued crater unit and an etched unit [1,2]. The subdued crater unit is a plains unit marked by subdued and buried old crater rims and was interpreted to be thin, interbedded lava flows and eolian deposits that partly bury underlying rocks [1,2]. The etched unit was described as being deeply furrowed by grooves that produce an etched or sculptured surface and was interpreted to be ancient cratered material degraded by wind erosion, decay of ground ice, and minor fluvial erosion [1,2].” M. G. Chapman “2001 SITE IN NORTH TERRA MERIDIANI: THE TES CONCENTRATION AREA” MSL99 Workshop available online at
 N. Hoffman “Outburst floods as cold and dry avalanches” available online at
 “Interpretation: We interpret the fan shaped deposits found at the base of the Olympus Mons escarpment as remnants of glaciers, in agreement with Lucchitta . It is important to consider what type of glacier. The con-tinuous, curvilinear ridges found on the surface of Unit C are very similar to rock glaciers. The source region, the basal escarpment, provides the topographic relief re-quired to provide the debris. The linear ridges found in the lower left region of the image are interpreted as the remnants of lateral moraines, which were deposited as the glacier retreated and then eroded again as the glacier advanced. This implies several episodes of advance and retreat.
However, there is no cirque-like source for the de-posits. Instead, they extend from somewhat linear seg-ments of the basal scarp. Additionally, the fan shaped deposits are much larger than terrestrial rock glaciers; they extend many tens of km rather than up to a few km. Thus, we interpret these features to be the remnants of debris-covered glaciers, which are morphologically simi-lar to rock glaciers but contain more ice and therefore flow more like valley glaciers and cover greater dis-tances.
We thus envision the following scenario: glacial ice builds up on the northwestern slope of the basal escarp-ment. Debris from the escarpment is deposited on top of the ice. As the glacier flows to the northwest, it spreads and develops a spatulate form. Several periods of ad-vance and retreat are recorded by the eroded lateral mo-raines. At the furthest extent of advance, the glacier de-posited a large terminal moraine. This moraine has now degraded, perhaps by sublimation of internal ice blocks or removal of debris through aeolian erosion. This has left the hummocky material in unit B.
Discussion: Lucchitta  also identified glacier-like features at the nearby Tharsis Montes. Recent analysis of MOLA topography data confirm this result and conclude that cold-based glaciers were once on the west-northwest flanks of Arsia Mons [16, 17] and Pavonis Mons [18, 19]. Cold-based glaciers are made up of ice that is entirely below the melting point; thus, it flows through internal deformation and there are no melting features associated with the glacier. It is likely that most mountain glaciers on Mars would be cold-based .
The glacial features found around the Tharsis Montes are far more extensive than those at Olympus Mons. This implies that a greater quantity of ice was available at the Tharsis Montes. Since all of these volcanoes are in the equatorial regions, it seems likely that they were glaciated at the same time. If water ice were stable at one location, it should be stable at the others. However, the fact that Olympus Mons had smaller glaciers implies that the conditions there were not as favorable for surface ice.
One possibility is that Olympus Mons was more active at the time; a higher geothermal flux in this region could prevent large build-ups of ice.” S. M. Milkovich and J. W. Head, III “OLYMPUS MONS FAN SHAPED DEPOSIT MORPHOLOGY: EVIDENCE FOR DEBRIS GLACIERS” Sixth International Conference on Mars (2003) 3149.pdf
 See Figure 1, also
“Introduction: Tharsis Montes cap the broad Tharsis Rise (Fig. 1), a huge center of volcanism and tectonism spanning almost the entire history of Mars. Each of the Tharsis Montes, although largely constructed of effusive and explosive volcanic deposits, contains a distinctive and unusual lobe, or fan-shaped deposit on their western flanks. On the basis of their unusual nature and superposition relationships, they have attracted attention since they were first described from Mariner 9 and Viking data . These deposits, as exemplified by those on Arsia Mons [e.g., 2,3], usually contain three facies: 1) An outermost ridged facies, consisting of a broad thin sheet characterized by numerous ridges, 1->10 km in length, and spaced a few hundred meters to several kilometers apart, that extend over topographic barriers without obvious deflection. 2) A knobby facies, which forms an extensive area of chaotic terrain that consists of surrounded several-kilometer-diameter hills; some hills are elongated downslope, and others form chains that are
parallel to subparallel to the ridges in the ridged facies. 3) A smooth facies, which contains arcuate lineations and
diffuse to lobate margins; the smooth facies appears to overlie areas of the knobby facies.” J. W. Head “MOUNTAIN GLACIERS ON MARS? CHARACTERIZATION OF WESTERN THARSIS MONTES FAN SHAPED DEPOSITS USING MGS DATA” Mars atmosphere modeling and observations workshop  available online at
 “In mid-October the frozen carbon dioxide, which seasonally caps Mars' north pole, evaporated enough to give Odyssey's scientists their first chance to look there for ice. "We are really excited about what we are seeing in the north polar region of Mars. With the seasonal carbon dioxide frost gone, we can see evidence of massive amounts of water ice in the soil, even more than we found in the south," said Dr. William Boynton, principal investigator for Odyssey's gamma-ray spectrometer suite at the University of Arizona, Tucson.” “NASA's Revealing Odyssey” MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20021207a.html
 “"Once the carbon-dioxide layer disappears, we see even more water ice in northern latitudes than Odyssey found last year in southern latitudes," said Odyssey's Dr. Igor Mitrofanov of the Russian Space Research Institute (IKI), Moscow, lead author of a paper in the June 27 issue of the journal Science. "In some places, the water ice content is more than 90 percent by volume," he said. Mitrofanov and co-authors used the changing nature of the relief of these regions, measured more than 2 years ago by the Global Surveyor's laser altimeter science team, to explore the implications of the changes.” Mars Odyssey and MGS Mars Orbital Laser Altimeter (MOLA) Science teams “Mars Odyssey Orbiter Watches a Frosty Mars" available online at http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20030626a.html
 T. N. Titus (Oak Ridge Associated Universities), H. H. Kieffer, K. F. Mullins (U.S. Geological Survey) “TES Observations of the South Pole” available online at http://www.mars-ice.org/crocus.html
 “Discussion: The narrowness of the size distribution combined with the size cutoff at smaller and larger sizes points toward a period in the history of this area of the residual cap where Swiss-cheese features were forming. It is hard to imagine what may be varying on timescales of centuries to control whether environmental conditions are suitable for Swiss-cheese formation or not. Orbital change cannot be playing a significant role over such short timescales and the atmosphere generally has no memory from one year to the next. One possibility is perhaps the slow redistribution of dust on a planet wide scale into preferred areas, which changes the albedo pattern with respect to the (by comparison) invariable elevation pattern. This could possibly switch the climate and circulation patterns into some other mode leading to differing conditions on the residual cap and a reseting of dust to its original configuration. This dust redistribution action may also act on more regional or local scales, changing the environment only in the near polar areas.” S. Byrne et al “Martian Climactic Events Inferred from South Polar Geomorphology on Timescales of Centuries” Lunar and Planetary Science XXXIV (2003) 3112.pdf
 “Introduction: The origin of the layering characteristic of the Polar Layered Deposits (PLD) of Mars is
generally not thought to arise from the flow of the water ice presumed (along with dust) to comprise
these layers, since rheological modeling indicates that Mars is presently too cold to permit substantial ice
flow in the polar regions. However, Martian obliquity deviates chaotically from its current Earth-like value of 25º, surpassing 45º within the last several Myr. Not only will the polar regions receive additional insolation at these high obliquities, but the resulting increase in H2O sublimation from the ice caps will initiate a water vapor greenhouse heating effect. Hence, surface and subsurface temperatures will be elevated at high obliquity, leading to dramatic increases in ice flow velocities.” Asmin V. Pathare and David A. Paige “Enhanced Ice Flow at High Martian Obliquity: A Rheological Model of the Polar Layered Deposits” Lunar and Planetary Science XXXI 1571.pdf
 “The observation of these changes and the rate at which they are occurring is akin to the observations of the "ozone hole" over Antarctica, or the steady increase in atmospheric CO2 in the Earth's atmosphere. Although the implications of these observations is often hotly debated (with most scientists convinced that they represent evidence for the impact of humans on the terrestrial climate), everyone agrees that they are evidence of contemporary climate change. Mars, too, is experiencing climate change today. We don't know what it means, or how extensive the changes may be, but we can now propose tests for future observations that can begin to address these questions.” Malin Space Science Systems Team “Evidence for Recent Climate Change on Mars” available online at
 “Introduction: Recent work has shown, surprisingly, that active channel systems exist in widespread but specific locations on Mars . Although conventionally interpreted as evidence for water flow, their context more firmly argues for the involvement of CO2 at cryogenic temperatures, and argues against liquid water. Channels within the South polar cap at 71o South are fresh and presumably carry annual flows as the pole cap ablates each spring. These are the freshest evidence for channels anywhere on Mars, with activity within the last Martian year. The temperature at this location has an annual mean around 200K making liquid water a very difficult proposition, in sufficient quantity to carry sediment 1.5 km downslope.” N. Hoffman LPSC  available online at
 A spreadsheet using this formula is illustrated here. By inserting coordinates of other images their Pole 4 latitude can be calculated.
 “Gullies seen on martian cliffs and crater walls in a small number of high-resolution images from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) suggest that liquid water has seeped onto the surface in the geologically recent past. The gully landforms are usually found on slopes facing away from mid-day sunlight, and most occur between latitudes 30° and 70° in both martian hemispheres. The relationship to sunlight and latitude may indicate that ice plays a role in protecting the liquid water from evaporation until enough pressure builds for it to be released catastrophically down a slope. The relative freshness of these features might indicate that some of them are still active today--meaning that liquid water may presently exist in some areas at depths of less than 500 meters (1640 feet) beneath the surface of Mars.” “MOC Images Suggest Recent Sources of Liquid Water on Mars”
MGS MOC Releases MOC2-234 to MOC2-245, 22 June 2000 available online athttp://mars.jpl.nasa.gov/mgs/msss/camera/images/june2000/
 “2. Occurrence in Regional Clusters. This observation was stated in the original paper , and is amplified by > 2 Mars years’ worth of data. Gullies occur in regional clusters. Gaps, in which no gullies occur between clusters, are observed. More gullies occur in the
southern hemisphere than the north.” K. S. Edgett et al “POLAR- AND MIDDLE-LATITUDE MARTIAN GULLIES: A VIEW FROM MGS MOC AFTER 2 MARS YEARS IN THE MAPPING ORBIT” Lunar and Planetary Science XXXIV (2003) 1038.pdf
 “Debris flows in French Alps: Best analogs to Martian gullies are debris flows from Greenland  and Canada  which occur over a permafrost. Debris flows in the Alps sometimes occur over a permafrost but this is not the case usually. They nevertheless consist of good analogs for the properties of the flow and the geometry. The two examples shown fit the association of alcove at the gully head and channel with levees. They have been triggered by snow melting in the springtime or strong showers in summer, thus external processes only. The debris flows of the Izoard do not show any springs at the head (Fig. 1). One spring has been observed in the valley 400m in elevation under the gully head and no debris flows alcove is observed at this location. The debris flows of Izoard formed in 1985 and they have overflow the road located at mid-slope. They are typically 10 m large with 2 m high levees.” N. Mangold et al “FORMATION OF GULLIES ON MARS: WHAT DO WE LEARN FROM EARTH?” Sixth International Conference on Mars (2003) 3048.pdf
 “3. Association with Layers. This observation was also stated in the original paper . We reiterate it here after examining ~1300 images. Any model for the origin of gullies must explain the relationship with layers. Gully channels typically head at a specific layer exposed on a given slope (e.g., Fig. 1). Within a given regional cluster, gullies may all head at the same layer where it is exposed in different crater and trough walls.” K.S. Edgett et al “POLAR- AND MIDDLE-LATITUDE MARTIAN GULLIES: A VIEW FROM MGS MOC AFTER 2 MARS
YEARS IN THE MAPPING ORBIT” Lunar and Planetary Science XXXIV (2003) 1038.pdf
 “Martian gullies discovered by Malin and Edgett  are widely regarded as evidence of recent hillside erosion by liquid water on Mars [2,3]. As reported earlier [3,4], Icelandic basaltic talus slopes of hillsides contain gullies that include virtually exact duplicates of
Martian gullies in terms of size, morphology, and placement with respect to blocky outcrops. At the 2001 LPSC, Costard et al.  and Lee et al.  also presented evidence of similar gullies in Greenland and Canada,
respectively.” William K. Hartmann et al “COMPARISON OF ICELANDIC AND MARTIAN HILLSIDE GULLIES” Lunar and Planetary Science XXXIII (2002) 1904.pdf
 “Global distribution of observed gully landforms” diagram in “True Colors of Mars by Schmidt  available online at
 “Gorgonum Chaos: The Gorgonum Chaos basin is an ancient, highly degraded 220-km diameter basin centered at about 37ºS and 173ºW. The basin itself lacks a well-defined rim, and probably was created through erosional integration of at least three impact basins that were subsequently mantled by thick air fall deposits during or prior to the earliest Noachian [1,2]. This basin, together with the nearby Atlantis, Newton, and Ariadnes basins have been suggested to have hosted deep lakes during part or most of the Noahian , and it has been suggested that at least once the lakes were deep enough to have formed an integrated basin overflowing to form Ma’adim Valles . The edges of these basins exhibit linear features that have been interpreted as possible shorelines . The present abstract focuses, however, on bench-like features at the bottom of the Gorgonum Chaos basin that appear to have been formed in association with a post- Noachian lake. The Gorgonum Basin is shown in Figure 1, with the general location of the post-Noachian lake outlined in cyan.” A. D. Howard and J. M. Moore “THE CURIOUS SHORELINES OF GORGONUM CHAOS” Sixth International Conference on Mars (2003) 3190.pdf
 “Image analysis: A thorough analysis of the MOC images coupled with a few simple climatic considerations suggest that these gullies are not so young. The gullies are not deeply incised and many of them are even filled up with detritus or dust-covered as can be seen in the upper part of Fig. 1 thus showing that the generating process acted only intermittently and was limited in time because no aquifer recharge has been available after their first formation.” G. Leone “GORGONUM CHAOS: ARE THE SEEPAGE-RUNOFF FEATURES REALLY RECENT?” Lunar and Planetary Science XXXII (2001) 1649.pdf
 “More speculative is our thinking on knob material origin. We note that the knob fields largely occur within five adjacent basins and within a restricted elevation range. Thus knob-material’s restricted occurrence implies that it was emplaced in a (or as a) medium that was limited in areal extent and possibly under a strong gravity-control, such as a fluid. If this material is volcanic then its susceptibility to modern wind erosion tends to disfavor emplacement by molten lava flows but doesn’t entirely rule out a subaerial pyroclastic density flow that didn’t significantly weld after emplacement. However, this argument is weakened by the absence of evidence for volcanic activity in the region. If the knob material was deposited in water, then its composition could either be fine-grained clastic lacustrine material or precipitates (evaporites). Such materials on Earth are relatively unindurated. All
but one very small knob field occurs within and below the 1100 m high-stand of a lake proposed by Irwin et al . The single exception is located in an isolated crater floor just SE of this putative lake and at a few 100 m above its reported high-stand.”
 “3. Gully Formation
 Recently, several groups have proposed that the young gullies [Musselwhite et al., 2001; Hoffman, 2001, 2000b; Draper et al., 2000] and many larger-scale features on Mars [Hoffman, 2000a; Hoffman et al., 2001; Jo¨ns, 2001; Parsons, 2001] may have formed from slope collapse
related to the presence of subsurface liquid or solid CO2 and
subsequent CO2 vapor-supported flow.” Sarah T. Stewart and Francis Nimmo “Surface runoff features on Mars:Testing the carbon dioxide formation hypothesis” JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. E9, 5069, doi:10.1029/2000JE001465, 2002
 “A clathrate mixture of CO2 and water ice, as long as it's under a fair amount of pressure, can actually exist in a solid form even if the ground is somewhat warmer than the melting point of ordinary water ice. If such a buried clathrate deposit was suddenly exposed by a landslide, the result would be a blast of liquid water -- squirted outward by the pressure of the vaporizing CO2 -- which could pour down the slope for some distance before vaporizing in the thin Martian air. [Since a rise in buried clathrate's temperature -- produced by geothermal warmth or a change in Mars' long-term climate -- could cause it to erupt in the same way, this is actually a variant on the "soda-water fountain" theory I described in Part 1 of my report -- except that the eruption of soda water would be released by "uncapping the bottle" through a landslide, rather than by through a temperature rise.] The obvious problem here is that, for the water part of the released clathrate to turn into liquid water rather than remaining a shower of ice fragments, the eruption would have to occur where the ground temperature was above 0 deg C. -- and the gullies are all in much colder areas. A possible way out of this problem, however, would be for the water part of the clathrate to be highly salty. As I mentioned in Part 1, some brines made out salts that are thought to be very common in Mars' soil -- such as magnesium sulfate and calcium sulfate -- have melting points dozens of degrees below that of pure water. And such "briny clathrates" might exist in solid form in these cold regions, but still be warm enough to turn into a short-lived torrent of liquid brine when a landslide released the pressure on them. There is also, perhaps, one more long-shot possibility. Carbon dioxide can't exist in liquid form under the 1-bar pressure of Earth's atmosphere (thus, frozen CO2 is known as "dry ice" because it sublimates directly from solid into gas). However, liquid CO2 can exist if the pressure is more than 5 bars -- and so there's a real possibility that large amounts of it may also exist underground in some regions of Mars. If a landslide released such a deposit, it just might remain liquid long enough to pour down a slope in the same manner as liquid water before boiling into gas. This, however, is unlikely -- Tanaka points out that such high-pressure liquid CO2 would explode into gas almost immediately on exposure to Mars' near-vacuum, and he thinks that - unlike released liquid water - it would have almost no time to pour down a slope in still-liquid form. Carr, however, disagrees, and that this theory cannot be completely ruled out.) Another problem is that for CO2 to be under enough pressure to exist in liquid form, it must be much more deeply buried than a water ice-CO2 clathrate -- under at least 30 meters of Martian soil and rock -- and landslides big enough to suddenly unearth such a deposit would have to be a lot larger. However, it's possible that a smaller landslide could make the covering layer of rock and soil over such a deposit shallow enough that the underlying pressure of the liquid CO2 could cause it to burst out into the open.” Bruce Moomaw “The Case For Outgassing” July 5, 2000 MARSDAILY.COM available online at http://www.spacedaily.com/news/mars-water-science-00g2.html
 “Evidence of drainage- The gullies in the CNewton crater have been discussed by Malin and Edgett (2000) who performed speculative scaling calculations to estimate the volume of water involving the discharge event. They concluded that about 2.5x106 liters of water were involved in each event, with nearly 100 channels active in the crater, giving a total of nearly 0.25 km3 of water that must have been discharged into the crater basin in a short period of time.” N. A. Cabrol et al “PROLONGED PONDING EPISODE IN C-NEWTON CRATER IN RECENT GEOLOGICAL TIMES ON MARS” Lunar and Planetary Science XXXII (2001) 1255.pdf
 “… approach in the Tempe Terra region. Geologic Setting: Tempe Terra is located on the northeastern flank of the Tharsis volcano tectonic province. It is an ancient terrain of Noachian age which has been cratered and heavily fractured. The western margin is embayed by volcanic flows originating from Tharsis and Alba Patera while the eastern margin is buried under probable alluvium from Kasei Valles and other outflow channels.” B.W. Harrington et al “EXTENSION ACROSS TEMPE TERRA, MARS FROM MOLA TOPOGRAPHIC MEASUREMENTS” 5th Conference 
 “Introduction: Numerous small volcanic edifices have been previously identified in the Tempe Terra  and Ceraunius Fossae regions of Mars [2, 3]. Low shield volcanoes dominate Ceraunius Fossae, while Tempe Terra has both low shields and steeper, possibly explosively erupted cones . These features are an interesting example of plains volcanism, and several comparisons have been made with terrestrial volcanic features. From Viking images, Hodges and Moore  used crater diameter/basal diameter (C/b) ratios for the Tempe volcanoes [C/b of 0.06-0.17] to suggest they may be similar to Mauna Ulu shield, Hawaii and low shields in the Snake River Plain, Idaho. Additional photoclinometric measurements made by Davis and Tanaka  of five volcanoes in Tempe Terra indicated morphological similarities to terrestrial cratered basaltic lava shields and tuff rings. Volcanoes in Ceraunius Fossae are less well studied, but previous work suggested they are similar to shields in Tempe Terra .” M. P. Wong et al “MOLA TOPOGRAPHY OF SMALL VOLCANOES IN TEMPE TERRA AND CERAUNIUS FOSSAE, MARS: IMPLICATIONS FOR ERUPTIVE STYLE” Lunar and Planetary Science XXXII (2001) 1563.pdf
 See Figure 1, E. Hauber et al “MORPHOLOGY AND TOPOGRAPHY OF FRETTED TERRAIN AT THE DICHOTOMY BOUNDARY
IN TEMPE TERRA, MARS: GENERAL CHARACTERISTICS” Lunar and Planetary Science XXXIII (2002) 1658.pdf
 “Nirgal Vallis is an ancient valley thought for nearly 3 decades to have been carved, in part, by running water at some time far back in the Martian past. Today the valley is, like the rest of Mars, quite dry. However, some of the high resolution Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images reveal small gullies on the walls of this valley system. An example is shown here (above, left), in which more than 14 channels nearly 1 kilometer (0.6 miles) long run down the south-facing slope of the Nirgal Vallis wall. Each narrow channel starts at about the same position below the top of the valley wall, indicating that there is a layer along which a liquid--most likely, water--has percolated until it reached the cliff, then ran down hill to form the channels and the fan-shaped aprons at the bottom of the slope. Some of the apron deposits seem to cover the dunes on the floor of the valley (lower 1/3 of the image), suggesting that the channels and aprons formed more recently than the dunes. The fact that neither the dunes nor the aprons and channels have impact craters on them suggests that these features are all geologically young, meaning a few million years at most, a few days or weeks at least.”
 J. R. Zimbelman “DECAMETER-SCALE RIPPLE-LIKE FEATURES IN NIRGAL VALLIS AS REVEALED IN THEMIS
AND MOC IMAGING DATA” Sixth International Conference on Mars (2003) 3028.pdf
 “Small valley networks on Mars: Two alternative modes of formation for the small valley networks on Mars are generally considered: a) the valleys resulted from surface runoff following precipitation or b) they
resulted from the release of groundwater, with or without the involvement of hydrothermalism [e.g., 2]. In some instances, a case for the possible role of sapping has been made (such valleys would belong to
“b”). For instance, Lee et al.  have reported ground ice sapping valleys within the distinctive impact breccia formation at Haughton crater, Devon Island, Canada, that are possible analogs to martian small
valleys such as Nirgal Vallis.
We interpret the Devon valley networks to be glacial meltwater channel networks: they formed as a result of the decay and retreat of an ice cover, possibly with intervals of glacial reoccupation. The proposed
mode of formation is supported by our observation that similar networks can been seen actively emerging at the margin of the ice cap in the eastern part of Devon Island. Both subglacial and ice-marginal streams, and in some instances supraglacial streams and their icemarginal
falls, were seen to present significant discharges and contribute to valley formation at several sites along the receding edge of the cap. The interpretation of valley networks on Devon Island as meltwater channel networks is consistent with the island’s overall landscape of glacial selective linear erosion, which suggests extensive former glacial occupation (mostly static ice) .” Pascal Lee and James W. Rice Jnr. “SMALL VALLEYS NETWORKS ON MARS: THE GLACIAL MELTWATER CHANNEL NETWORKS OF DEVON ISLAND, NUNAVUT TERRITORY, ARCTIC CANADA, AS POSSIBLE ANALOGS” Fifth International Conference on Mars 6237.pdf http://www.lpi.usra.edu/meetings/5thMars99/pdf/6237.pdf
 Figure 6 Nature Insight: Review article Hale Crater http://www.nature.com/nature/journal/v412/n6843/fig_tab/412228a0_F6.html
 “Interpretations: I interpret the viscous-flow features as ice, glaciers, and rock glaciers derived from seepage and eroded valley wall material associated with gully and alcove formation [1 and 2]. I suggest that ice formation and accumulation have occurred on the NW wall of the valley under conditions of relatively low sublimation due to reduced insolation on pole-facing slopes . Ice and ice-rich debris built up over time and began to flow under the influence of gravity in the form of glaciers and rock glaciers. These eventually reached the floor of the valley and continued to flow until areas of higher insolation were encountered. In these areas, the sublimation rates were high enough to ablate the glaciers to the point that they could advance no further.”
J. D. Arfstrom “UPPER DAO VALLIS: A BASIN DOMINATED BY ICE-RICH VISCOUS MATERIALS” Lunar and Planetary Science XXXIV (2003) 1208.pdf
 “Observations: The ice formations on the slopes of Dao Vallis appear to be tributaries of an even more extensive ice formation on the floor of the valley (Figure 1). The ice formations of the slopes merge with the ice formation at the bottom of Dao Vallis in a way that suggests mutual flow, closely resembling the way terrestrial tributary glaciers merge with main valley glaciers (Figure 2). The ice formations on the
slopes and floor of Dao Vallis possess distinct structural morphologies that are characteristic of terrestrial alpine glaciers (Figure 3).”
J. D. Arfstrom “PROPOSED MARTIAN GLACIERS OF RECENT AGE AND A MODEL OF THEIR FORMATION” Lunar and Planetary Science XXXIII (2002) 1092.pdf
 “Cosmetic alterations A dirty ice sheet that once extended over Mars’s mid-latitudes would explain several
enigmatic features there. Some of these have puzzled planetary scientists ever since the two Viking orbiters returned images in the late 1970s that looked for all the world like ice-related surface features on Earth. Most suggestive of ice, perhaps, were places where the surface seemed to be sloughing off the land and oozing downhill. Generically termed “viscous flow features,” they looked like the work of Earth’s rock glaciers, streams of flowing rock-laden ice. Many more have since turned up in close association with the dissected mantling spotted by Mars Global Surveyor. In the 13,000 MOC images they have inspected, Milliken and his Brown colleagues reported at the workshop, viscous flow features are restricted to the same 30° to 60° mid-latitude bands as the dissected mantling. The flows peak in abundance at the same 40° latitude as the dissected mantling.
Furthermore, the mysterious gullies—where liquid water seems to have flowed down steep slopes in the recent past—follow the same latitudinal distribution as viscous flow features and dissected terrain; they even tend to cluster in the same three or four places as the viscous flow features do. The currently favored explanation for gullies is that lingering patches of dirty snow melted there (Science, 28 February, p. 1294). Taken together, the Brown researchers say, these features could be explained by the warming of an ice-rich mantling. That could have produced meltwater that formed gullies, ice softening that gave rise to viscous flow, and ice loss through sublimation that weakened the mantling and allowed dissection. “That’s consistent with what I’ve seen” in images, says planetary geologist James Zimbleman of the Smithsonian Institution’s National Air and Space Museum in Washington, D.C. “I’d call it a working hypothesis.” “Iceball mars?” 11 APRIL 2003 VOL 300 SCIENCE www.sciencemag.org available online at
 “At a press conference and in a paper published online by Nature on Wednesday, planetary scientist Phil Christensen of Arizona State University proposed a new idea to explain the creation of the martian gullies. He suggests they could have been carved by water melting from snow banks.” Vanessa Thomas “Snow May Have Carved Martian Gullies” Astronomy.com available online at
 “4. Occurrence of levees: Levees on each sides of the channels are typical of a particular kind of flows
with a yield strength . The yield strength corresponds to the minimal shear strength the material needs to reach before to flow. They are typically associated to flows containing 50 to 90% of solid particles (silt to pebble size) . In Izoard, levees are 2 m high for a 10 m large channel, a size comparable to gullies observed on several MOC images. The existence of levees implies the incorporation of meltwater in the debris over a significant thickness of material. This is possible only if thawing of the ground occurs over a significant thickness (several tens of cm), on the contrary to the model of snowmelt proposed by Christensen  under present conditions. The ratio of water to sediment of 10:1 proposed by Christensen (so 10% of rock) is also not in the range of debris flows with levees which are characterized by a proportion of more than 50% of rock . Nevertheless, if existing during high obliquity periods, the presence of snowpacks would favor the process of debris flows because snowmelt can efficiently fill the porosity of debris as observed in cold regions in Greenland  or North Canada .” N. Mangold et al “FORMATION OF GULLIES ON MARS: WHAT DO WE LEARN FROM EARTH?” Sixth International Conference on Mars (2003) 3048.pdf
 “Now UA researchers propose an alternative explanation involving carbon dioxide erosion. They point to several reasons why CO2 is a better candidate than water in gully formation. One reason is that most gullies are found in the southern highlands, the oldest and coldest part of the planet, a place where liquid water is least likely to be stable.
"That's high altitude in a region of low geological activity. It is difficult to invoke some hydrothermal action there," Musselwhite said. "The surface is old but the gullies are new."
Another reason is that the southern hemisphere has more extreme temperature variations throughout the year than does the northern hemisphere, a result of the fact that Mars is closer to the sun during southern summer and farther away during southern winter, Musselwhite said.
The gullies are generally on pole-facing slopes where they receive very little or no sunlight for most of the year.
However, Musselwhite said, the most compelling fact is that gullies always start about 100 meters below the top of the cliff. At that depth, the pressure of the rock overhead is just enough for liquid CO2 to be stable, if the temperature is low enough.” Agnieszka Przychodzen “Exotic CO2 Process May Have Carved Martian Gullies” MARSDAILY April 2, 2001 available online at http://www.spacedaily.com/news/mars-water-science-01f.html
 See Figure 3
“3. The Role of Water
 The observed geographic (Figure 4), temporal (Figure 5), and azimuthal (Figure 6) correlations provide evidence for a connection between slope streaks and a surface temperature near the triple point of water, suggesting that the formation of streaks involves a phase transition of water. For instance, melting could provide lubrication of avalanches, or mass movements could be triggered by sublimation at the solid-gas transition. The analysis presented does not pinpoint a specific mechanism for slope streak formation, and hence we do not elaborate on any particular one, but consider the potential role of water generically.
(See also Ferris et al. .) While alternative explanations not involving water, such as patterns in atmospheric dust transport, can be envisioned, the observations are simply accounted for if water plays a role, either in triggering the mass movements or in controlling dust deposition.” Norbert Schorghofer et al “Slope streaks on Mars: Correlations with surface properties and the potential role of water” GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 23, 2126, doi:10.1029/2002GL015889, 2002 available online at
 “When examined in detail individually and as a group it appears that the seep features have far more characteristics associated with liquid flows than with flows of dry dust or slurries. The equatorial location of the seepages, clustering in the Tharsis region (and 180 degrees away north of the Hellas Basin) plus physical flow attributes, indicate that water (or possibly some other liquid) may be involved in their genesis. As we have demonstrated, these features are currently being formed on the Martian surface. These circumstances together imply that it is highly likely that water is now present on the surface of Mars.” Efrain Palermo, Jill England and Harry Moore “A Study of
Mars Global Surveyor (MGS)Mars Orbital Camera (MOC) Images
Showing Probable Water Seepages. Are They Dust Slides as NASA Claims or Proof of Water on Mars?” available online at
 See Figure 3 R. Sullivan et al “MASS-WASTING SLOPE STREAKS IMAGED BY THE MARS ORBITER CAMERA” Lunar and Planetary Science XXXI 1911.pdf
 “Summary. We conclude that dark streak formation on Martian slopes is fundamentally similar to small mass-movements that have occurred on debris-covered steep slopes elsewhere on Mars; distinctive dark streak features result where small mass-movements occur in the presence of a thin, potentially mobile dust mantle. They cannot be easily interpreted as a dark fluid stain or float moving downslope from a point source.”
R. Sullivan et al “MASS-MOVEMENT CONSIDERATIONS FOR DARK SLOPE STREAKS IMAGED BY THE MARS ORBITER CAMERA “ Lunar and Planetary Science XXX 1809.pdf
 “Crystalline hematite has been mapped over an area in Sinus Meridiani approximately 500 km in longitude extending approximately 200 km in latitude . The extent of this deposit very closely matches the geomorphic boundary of a smooth, layered, friable unit that is interpreted to be sedimentary sedimentary in origin [3, 9]. This material may be the uppermost surface in the region, indicating that it
might be a later-stage sedimentary unit, or alternatively a layered portion of the heavily cratered plains units. A second accumulation of hematite approximately 60 x 60 km in size is observed in Aram Chaos (2° N, 21° W). This site is also associated with layered materials and a water-rich environment.” P.R. Christensen et al “THE DISTRIBUTION OF CRYSTALLINE HEMATITE ON MARS FROM THE THERMAL EMISSION
SPECTROMETER: EVIDENCE FOR LIQUID WATER” Lunar and Planetary Science XXXI 1627.pdf
 “Figure 4. Crater count diagram and isochrons for the Terra Meridiani hematite-rich area. Filled symbols show the population of "fossil craters" lying near the saturation equilibrium limit (upper straight line), indicating a very ancient surface. Open symbols show the fresh, recent craters created since the modern surface formed, indicating that the area has been exposed for as little as a few million years. Our interpretation is that an ancient (paleolake bed?) was covered by sediments and exhumed only a few million years ago.” Melissa D. Lane et al “UPDATE ON STUDIES OF THE MARTIAN HEMATITE-RICH AREAS” Lunar and Planetary Science XXXII (2001) 1984.pdf
 “Mineral abundance maps (Fig. 5) show basaltic lithologies for much of the VM interior, in the form of high- and low-Ca pyroxenes (up to 24% total) and plagioclase minerals (up to 28%) in layered deposits in the walls and interior, as well as in dark materials at the base of canyon walls. Note that the presence of surface dust in parts of Ophir and east Candor Chasmata appears to decrease the apparent abundance of minerals in these areas. The distribution of gray hematite agrees well with previous results , but we see only (~8%) a small enrichment of red hematite in the possible hydrothermal site in west Candor  (Fig. 6).” L.R. Gaddis et al “MINERAL MAPPING IN VALLES MARINERIS, MARS: A NEW APPROACH TO SPECTRAL DEMIXING OF TES DATA” Lunar and Planetary Science XXXIV (2003) 1956.pdf
 “Our observations of hematite in the VM are similar to those seen by Christensen et al., .” F. S. Anderson et al “MINERALOGY OF THE VALLES MARINERIS FROM TES AND THEMIS” Sixth International Conference on Mars (2003) 3280.pdf
 “Aram Chaos is a 280 km diameter crater centered at 2.5N, 338.5 E. Like other nearby craters, it has been filled with a large amount of material since its formation . It is connected to the Ares Vallis
outflow channel by a small, 15 km wide channel that flowed outward, from Aram Chaos to Ares Vallis. The association of Aram Chaos with the outflow channels, as well as its obvious basin morphology,
indicates a possible connection to past surface and subsurface water in the region.” Timothy D. Glotch and Philip R. Christensen “The Geology of Aram Chaos” Lunar and Planetary Science XXXIV (2003) 2046.pdf
 “There are a number of reasons to proceed with numerical modeling of sand transport at this time. Most importantly, the wind regime near the surface is strongly influenced by topography, and the first accurate map of global topography from MGS MOLA has only recently become available. Mars GCM’s now appear to adequately simulate the circulations during dust storm periods, which produce some of the strongest surface winds . Finally, Mars GCM’s now have the flexibility to examine wind regimes from different epochs. We have used surface wind output from the GDFL Mars GCM to build a global sand transport model for Mars. Several parameters have the same values used by Anderson et al.  in order to directly compare the Ames GCM output with that of the GDFL GCM. We compare the resulting sand distribution with the known sand dunes on the Martian surface. We also compare our results with those of Anderson
et al. . The RDP/DP is also calculated along with the sand transport, and these values are compared with known dune forms and orientations as well as to the results found by Lee and Thomas  with the Ames GCM.” L. K. Fenton and M. I. Richardson “GLOBAL MARTIAN SAND TRANSPORT AS PREDICTED BY THE GDFL MARS GCM” Lunar and Planetary Science XXXI 2072.pdf
 “Sand dunes are representative of these types of landforms. With nearly three years of high resolution observations of relatively small dunes, no evidence whatsoever has been found to support the contention that any dunes on Mars are presently mobile. Yet their dune crests appear to be quite sharp (inactive dunes still shed sand from their
crests and become rounded with age), and subtle markings on their slip faces suggest that a small amount of avalanche sand may move under the added weight of winter snow. Occasionally, dunes exhibit striations that suggest that their surfaces may be cemented or crusted, but for the most part their inactivity in the presence of winds likely to be able to move sand (we see dust-devil tracks on some dunes) suggests that their inactivity may be related to some environmental factor, such as the absence of locally sustained winds.” M. Malin and B. A. Cantor “MARS ORBITER CAMERA CLIMATE OBSERVATIONS” available online at http://www-mars.lmd.jussieu.fr/granada2003/abstract/malin.pdf
 “Exposures of layered materials in western Candor Chasma illustrates yet another incongruent relationship: these layered outcrops display very few impact craters on their surface. Indeed, they show crater densities two to three orders of magnitude lower than those seen within the summit caldera of Arsia Mons (Figure 3). Since the evidence is very good that these materials are ancient and being exhumed, the absence of craters means that the layers have been recently exhumed, or that their surfaces have been recently eroded (if the Arsia Mons caldera is of the
order of hundreds of millions of years old, then the surfaces in Candor are only hundreds of thousands to millions of years old, and in cases where there are no craters at all, even younger). We see no evidence of the process that has exposed these materials, and no evidence for where the materials have gone. There is certainly nothing acting today that could create what we see. This landscape, too, is not representative of the present-day suite of processes.” Ibid. available online at
 “Two basic processes are portrayed: deposition of sediment as dust settling out of the atmosphere, and deposition in bodies of water such as crater lakes and shallow seas.
The chief source for sediment in both cases may be a combination of materials produced by explosive volcanism and meteorite impact, as well as weathering and erosion, researchers said.
Malin and Kenneth Edgett have suggested that the some of the layers may have formed underwater in lakes or perhaps shallow seas inside craters.
If the sediment fell from the air, then some recurring phenomenon would have had to create thin layers of regular thickness and properties -- the type of deposition that occurs in bodies of water.
Malin and Edgett explained how deposition from the air might have occurred. The atmosphere's pressure might have varied on a regular basis from something that is hundreds of times thicker than it is at present to something that is perhaps only tens of times (or less) thicker than it is today. As the atmospheric pressure went up, it could have carried more dust to be deposited; as it went down, there would have been less.
It is also possible, the researchers say, that the layers were created by a combination of deposition from the air and from water.
"Ultimately, geologists will have to go to Mars," Malin said, "to investigate the changes in ancient Martian environments recorded in these rocks."
Jack Farmer, director of the astrobiology program at Arizona State University, said standing water is the most likely explanation for the layering.
"This truly is exciting stuff," Farmer told SPACE.com. "If true, it indicates that water-lain sediments could be much more widespread than we thought previously." http://www.space.com/scienceastronomy/solarsystem/mars_sediment_pics_001205.htmlMORE IMAGES: Martian Sediment Layers Explained”
 “HOUSTON,TEXAS—Planetary scientists poring over the latest data returned by Mars orbiting spacecraft have reached a startling conclusion: Half the Red Planet appears to have been encrusted with ice in the relatively recent past. A layer of dirty ice still covers Mars poleward of latitudes that, on Earth, would encompass Anchorage, Moscow, and South America’s tip. But several lines of evidence suggest that, within the past million years or so, a now-vanished ice layer cloaked Mars down to the latitudes of Buenos Aires, New Orleans, and Baghdad. This icy coating would not have been the first to cover large areas of Mars, according to new climate modeling reported last month at a workshop here.* Mars has a tendency to wobble back and forth on its axis, and the new modeling suggests that this instability would have triggered a succession of ice ages throughout the planet’s history. The tilting would have shifted polar climes to lower latitudes, vaporizing the polar ice caps and layering dirty ice toward the equator. That would help explain much geology that has puzzled researchers for as long as 30 years: swaths of “softened” martian terrain that look like they’re made of ice cream scooped on a hot day, slopes that ooze like wet paint dripping down a wall, and even the enigmatic gullies where water seems to have flowed on a frozen planet. More speculatively—and farther back in Mars history— extreme tilting of the planet may have repeatedly driven ice sheets right down to the equator. If so, that ice is gone now, but the dust left behind could have formed the mysterious layered sediments of the equatorial region.” “Iceball Mars?” 11 APRIL 2003 VOL 300 SCIENCE www.sciencemag.org available online at
 “Recent research has confirmed the observation that extensive areas of Mars are dominated by layered terrain. Layers exist everywhere - even within craters. This poses two main problems, depending on the interpretation of the origin of the layers.
If the layers are sedimentary, then it implies an active early sedimentary history for Mars, involving a far stronger hydrological cycle than we have evidence for. If early Mars were this active, then all the early craters should have been wiped away, yet they are largely unaffected. In addition, layering exists within many unbroken craters, without sign of an entry or exit channel. It is as if the layers had fallen from the skies.
If the layers are lavas, then it implies a much greater early volcanic history than we see evidence for. Again, many of the large early craters should have been destroyed or buried, and we should see evidence for many more volcanic vents and fissures than we do in fact see. In one way, the volcanic model can explain the layers in enclosed craters. Massive volcanic eruptions could have formed ash clouds that rained down into the craters, yet we don't see the vents.
Here are the seeds of yet another Mars paradox. The evidence is internally contradictory. We see layers, yet no sign of the processes that caused them or the likely side effects of those processes.” N. Hoffman “Origin of Layering on Mars” available online at http://www.earthsci.unimelb.edu.au/mars/Layer.html
 “Analysing the spectra from the ten different bands of infrared light the instrument can detect, the THEMIS team has begun to identify specific mineral deposits, including a significant layer of the mineral olivine near the bottom of a four-and-a-half kilometer deep canyon known as Ganges Chasma. Olivine, Christensen notes, is significant because it decomposes rapidly in the presence of water. "This gives us an interesting perspective of water on Mars" he says. "There can't have been much water – ever – in this place. If there was groundwater present when it was deep within the surface, the olivine would have disappeared. And since the canyon has opened up, if there had ever been water at the surface it would be gone too. This is a very dry place, because it's been exposed for hundreds of millions of years. We know that some places on Mars have water, but here we see that some really don't." “Olivine points to dry Mars” June 6, 2003 available online at http://www.geolsoc.org.uk/template.cfm?name=THEMIS
 For a good novel based on life surviving these impacts that may have killed the dinosaurs there is “Evolution” by Steven Baxter.