The Spirit and Opportunity landing sites as former Martian Poles

Abstract:

Mars has many enigmatic features, such as Tharsis, Olympus Mons, Valles Marineris, and Alba Patera. The volcanoes and Valles Marineris are huge compared to the size of Mars with no apparent explanation for what made them. In the theory outlined here the poles of Mars wandered through history in response to 4 major impacts, Utopia, Isidis, Argyre, and Hellas. As each impact occurred the large negative mass of the crater tended to attract a rotational pole to it, and then later as large volcanoes formed the mass of these tended to move to the Equator. The combination of these events caused the poles to move over much of Mars spreading water and ice signs along its path, and often leaving the rest of Mars dry by comparison. This would account for how Mars shows so many water and ice signs in some areas and appears so dry chemically in others. In this paper only part of the polar path is shown, from south of Valles Marineris the pole moved to Meridiani Planum where the Opportunity rover is now. The opposite pole, which eventually became the current North Pole moved from the area of the Isidis Crater to the area around Gusev where the Spirit Rover is. We show how these areas are geologically consistent with former poles, and how this polar path implies a watery zone, possibly habitable for hundreds of millions of years. This would be sufficient for life to possibly evolve substantially if it existed at this time.

 

Keywords: astrobiology, crinoid, Gusev, Mars, Meridiani,, Opportunity, polar, Spirit, water.

 

This theory originally came about from reading a paper by Sprenke and Baker[1] on a proposed polar wander path on Mars. In the process of examining this we accumulated published papers referring to features along this path, and looked at whether features there were consistent with having been on a pole.

 

 Typically such features would be formed by water or ice, and the terrain would be similar to known geology we see on the current poles. This was contrasted with areas off this polar path, which typically were much drier and ice free. Because the proposed polar path went back to before Tharsis, Olympus Mons and Valles Marineris it became possible this path was directed by the same forces that made these formations, and much of the current Martian landscape. We found that virtually every single paper published on Martian geology is consistent with this polar wander path.

 

Because these large volcanoes have so much mass they tend to move to the Equator, and so these could only form at certain times in the polar wander. The polar path if correct then implies when these Mons formed and also when large craters formed as their negative mass would tend to attract the pole to them. Once the correct polar path is known, then every other Martian feature with a significant impact on the gravitational balance of Mars should only occur at certain points along that path.

 

Because of space limitations and the serendipitous landing of the Rovers on two former poles opposite each other, we have reproduced here the middle part of the polar path. In the next paper we will show the possible events before this section that formed Tharsis Montes, Olympus Mons, Elysium Mons, and Valles Marineris. A following paper will carry on after this one, with the Hellas impact attenuating the Martian magnetic field and moving the pole to Hellas Crater, and then its current position.

 

While it is not known if life exists on Mars the polar path strongly implies a habitable zone existed around these poles as they wandered across Mars, for hundreds of millions of years or more. The large volcanoes of Tharsis, Elysium Mons, and Elysium Mons may have heated the planet, as they are associated with parts of the polar path that appeared to generate huge amounts of water.

 

In the three papers we will refer to 5 pole positions as being stable for a time, and the polar movement between these positions. The current pole positions we call Pole 5, and the polar movement from Pole 2 to Pole 3 is discussed here, Pole 4 is near Hellas Crater. To follow this path a good map of Mars is essential as many of the names are obscure. If you Google and download “mola_regional.pdf”[2] this map shows all the place names referred to here. For any image numbers, placing the image number in a search engine and selecting the link from msss.com is the fastest way to find them.

 

In this paper we concentrate on the movement from what we call the South Polar Cap 2 position near Solis Planum (south of Valles Marineris) to South Polar Cap 3 position at Meridiani Planum, shown in Figure 1. The associated North Pole moved from the North Polar Cap 2 position around Isidis Planitia eastward to near Lucus Planum as the corresponding North Polar Cap 3. We call this North Polar Cap 3 because eventually it will go to the current North Pole position. In this theory the Argyre impact starts the polar wander from the second to the third position.

 

The path begins when the Pole is moving eastwards from the South Polar Cap 2 position around Solis Planum, to north of Argyre Basin into Margaritifer Terra and then east to Meridiani Planum, the site of South Polar Cap 3. One should remember that a pole is very large in its influence, so the exact position of the centre is often not significant. For example the current poles are quite asymmetric in shape compared to the rotational pole itself.

 

There is no direct evidence for the Polar Cap stabilizing or remaining in Margaritifer Sinus for any great length in time along this route. Figure 1 shows this path, South Polar Cap 2 to 3 is from Solis Planum to Meridiani Planum.

 

 

Figure 1: The proposed polar wander path from Pole 2 to 3.

 

The large river networks in the Xanthe Terra and Margaritifer Sinus areas imply the atmosphere at the time was much thicker, since water would need a much higher air pressure than found today.  A higher polar obliquity may have also contributed to this. The axial tilt of Mars is believed to change periodically over time, and when the angle is greater the ice around the poles is thought to melt or sublimate much more.

 

This gives a possible habitable environment at this time, with abundant water, heat from the Argyre impact, and higher air pressure. These water signs persist all the way along the polar path to Meridiani Planum. 

 

According to Grant[3] Margaritifer Sinus contains remnant high valley densities, which is consistent with a moving pole and ice melting. This area was resurfaced several times[4], perhaps from the subsequent volcanism related to the Argyre impact. Therefore, ice may have partially vaporized, sublimed or melted, either due to impacts, and/or due to subsurface heat from associated geothermal activity. While Grant[5] believes some precipitation occurred, most ground water would be consistent with a water table associated with either a forming or sublimation/melting of an existing pole. The Parana Valles[6] drainage system is particularly extensive. Therefore, according to Grant[7], groundwater discharge[8] must have continued for some considerable time. The length of time referred to would likely be sufficient for life, if present to evolve substantially.

 

Lewis and Aharonson[9] examine Holden Crater and the distributary fan discovered in it. This area is near Argyre Crater and implies liquid water was discharged from the Polar Cap nearby. Pondrelli et al[10] also examine the area and how it connects the Argyre Basin to the northern channels. Williams et al[11] report on fans in Xanthe Terra, along the path of the Polar Cap.

 

Hynek et al[12] suggest that the fluvial resurfacing in this area lasted for a period of some several hundred million years. A combination of rainfall and sapping[13] appear likely, so lakes may well have formed[14]. Polar wander may link the two main theories of precipitation and sapping, hence explaining the extensive valley networks[15].

 

According to Nelson ice may have periodically melted. An examination of Margaritifer Sinus, by Philips et al[16] concluded that much of the Tharsis bulge was already in place before the drainage channels formed. This is consistent with the general rise in elevation in the area of Tharsis and Sinai Planum from the Argyre impact. At this time Tharsis and Olympus Mons would have been growing after the Argyre impact, and their extra weight would tend to move to the Equator. This would have the effect of forcing South polar Cap 3 to move eastwards to Meridiani Planum. This part of the polar path (and its antipodes, the future North Pole) shows abundant evidence of water and ice. The area around Margaritifer Sinus was plausibly a habitable zone and the Rover Opportunity has now shown Meridiani Planum was a habitable zone. In between these two there are enough water signs to imply this was a long period of Martian history in which a habitable zone existed. It is not known however if there was life there to take advantage of this.

 

During the late Noachian, Tharsis Rise was large enough to direct the channels northward. Large amounts of material eroded from this area were transported along these channels, most probably as a direct result of basal water erosion during  melting (and sublimation) as the Pole moved north east of Valles Marineris[17] [18] towards Margaritifer Sinus.

 

By the time the Polar Cap had moved north east of Valles Marineris water and ice would have accumulated in it as the Polar Cap melted and moved from the Argyre impact event, which may explain the paleolakes[19] there. Carr[20] suggested that ground water flowed into Valles Marineris and then into Chryse Planitia, forming lakes. Rossi et al[21] believe there is good evidence of ice and glaciation, consistent with a polar area adjacent to and south of the Valles Marineris at that time. Glacial features in the area support this interpretation.

 

Lunae Planum would also have received water from the moving and melting of the pole. Shalbatana Valles originates in the chaos on Lunae Planum (Greeley and Kuzmin[22]). Interestingly this would have resulted from a probable impact basin that formed a catastrophic outflow.

 

Nelson and Greeley[23] discuss three major fluvial events in Xanthe Terra, with indications of surface water flow. The first is a broad sheetwash from the Valles Marineris area, perhaps coinciding with the Argyre impact. Following this more extensive flooding occurred, forming Shalbatana, Ravi, Simud, Tiu, and Areas Valles. This may coincide with the pole migrating to Margaritifer Sinus. The majority of surface water was sourced from chaos areas[24]. This gives a direct link to the Argyre area and perhaps to that impact.

As we follow the polar wander, the fluvial-features seem to overprint other terrain, so flooding may have continued as the Polar Cap migrated.

 

At the antipodes North Polar Cap 2 near the growing Elysium Mons started to move eastward. This area has many signs of ice and water, for example M0901921, M0905888, M0906366, M1001498, M1900226, M1902068, M2000840, and M2000907. Again these photos from the MOC can be seen by placing the image numbers in a search engine and selecting the link from msss.com. Further signs can be seen in Martei Valles in M2001192, M2200885, and SP238804. Lanagan et al[25] see evidence of fluvial flows associated with Elysium Mons and lava flows in the area, and rootless cones[26] also indicate ice in the area.

 

The new Odyssey results of subsurface ice[27] indicate a large deposit on the equator in Babaea Terra. A second area of ice occurs on the left edge of the map, just below the equator. This corresponds to the location of the opposite North Polar Cap 3. According to Sprenke et al the South Polar Cap moved in a curve to 0S 330W, almost into the centre of the ice rich area at Meridiani Planum. We call this area South Polar Cap 3. The geology and the geophysical data indicate icy areas on opposite sides of the planet. When we calculate the radius of the planet and adjust for any faulting, the result suggests that these areas were almost certainly a polar pair. For each Polar Cap pair we back-calculated the polar separations. The differences in diameters are almost perfectly offset by the thickness of rift-like valleys and fault movement and by assuming earth-like passive fault movement the polar age relationships could be back calculated.

 

We believe the poles stabilised in these ice rich areas for a long time, also with ample evidence of water signs. Thus the possible habitable zone extends to the results we see from the Rovers and implies similar chemistry and water signs may be found along this whole polar path from Solis Planum.

 

Rift-like faults, glaciation, evidence of surface water, and even volcanic activity tend to track the polar movement. The movement of Pole 2 to Pole 3 adds to approximately 150 degrees of longitudinal movement so this is consistent with Tharsis forming near South Polar Cap 2 and then moving nearly 180 degrees to the Equator, which pushed the poles about 150 degrees eastward.

 

In this time Tharsis had to be growing so it would have been adding a lot of heat to the atmosphere, and initially along with the newly formed Argyre Crater parts of South Polar Cap 2 would have overlaid these hot areas, melting water and CO2 if frozen. This would thicken the atmosphere and perhaps create snow or precipitation away from the heat. Tharsis and Argyre, with Elysium Mons then could have supplied the heat for this potentially habitable zone to last so long. This would also explain why Mars has so many water signs when it should have been too cold for most of its history. The overall temperature of Mars probably remained low, inhibiting the destruction of olivine even in the presence of water.

 

South Polar Cap 3 assumed a position between the Argyre and Isidis impact basins as each, being low gravity (low mass) would tend to be close to this pole.  When this occurred the Pole 3 positions would attain a stable configuration. Tharsis was by this time near the Equator and South Polar Cap 3 was near the two main negative masses of the Argyre Crater and Isidis Crater, with Utopia Crater a lesser influence.

 

Interestingly, South Pole 3 coincides with an area of heavy Noachian cratering[28] and the second cratered area corresponds well with the opposite North Pole 3. 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 seems to have been stable for a long enough time for 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.

 

Volcanism seems to follow the polar wander, so is either related to the shock waves from impacts or is a late stage effect, occurring in relation to degassing (geothermal activity) during faulting of polar valleys. This would explain how volcanoes have apparently restarted in Martian history and the surface is relatively young in parts.

 

Rift-like, passive, or strike-slip valleys would be thus be overprinted by basal melting of icecaps and related sublimation. Most large catastrophic flood (outburst) features occur adjacent to these poles so may be triggered by increased geothermal heat. Pole 3 likely remained in a stable location through this resurfacing.

 

These crater areas are linked into what is termed the Noachian age. Thus, 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 Polar Cap may have slowly moved and protected other areas for a time in its path. In a later paper we will show a large northern ice sheet or ocean would have sublimated after the Hellas impact, exposing the terrain referred to as Amazonian. The two impacts then may have caused the features known as Hesperian and Amazonian to form. This makes it difficult to estimates times for these events as the polar path would have obscured and altered crater counts.

 

In moving from Pole 2 to Pole 3, the polar ice closely follows and may have formed or modified the dichotomy boundary. The main dichotomy 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 Polar Cap 2 moved from 12.7S 92.6W eastward to around 0S 330W, which is approximately 122 degrees of longitudinal movement or approximately 1/3 of the total great circle. The opposite pole migrated 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 244 degrees of movement over a dichotomy boundary of 270 degrees as a polar wander path. The rest can be explained by the width of the edge of South Polar Cap 3 at 330W in Meridiani Planum, which makes it appear to extend further east. Thus virtually the entire visible dichotomy boundary falls on the same line as the movement of Pole 2 to Pole 3.

 

The Northern Lowlands represents a paradox. It is so large a negative mass that it would likely prevent the Polar Caps moving along the path proposed by Sprenke and Baker. Smith and Zuber[29] say that Hellas Crater for example is only 10% of the volume of the Northern plains. Thus its gravitational influence would be greater than either Argyre or Hellas.

 

Therefore if this polar path is correct the Northern Lowlands was partially covered in water or ice early in Martian history, neutralising its negative mass. Oner et al[30] make some estimates of its size. This would make the planet more balanced and not impede polar wander. Indeed this ice or ocean had to exist for this polar wander to occur, so proving polar wander proves the northern ice sheet existed. The Northern Lowlands is so large a negative mass that the poles could never have moved from their current position without water or ice to fill in the low areas. Hence polar wander implies this water or ice existed, and the shape of the ice rich areas at 60N shown by THEMIS implies at least parts contained more ice at some point.

 

Early in the history of Mars the Northern Lowlands may have had other impacts such as a Borealis impact lowering this area. Water and ice just as on Earth would have migrated to the lower areas balancing the planet. Over time the water would have smoothed out these ancient craters, as it may have also done with Utopia Crater.

 

The polar wander path along the dichotomy boundary may have been on a pre existing slope, altering its shape with ice and water erosion. A Polar Cap moving on a slope like this would tend to have a runoff of water heading north, accounting for the smoother surfaces in Acidalia, Arcadis, Amazonis, and Elysium Planitia.

 

THEMIS[31] shows some evidence of such a runoff. Blue ice rich areas extend from the polar path south west of Elysium Mons and north to a huge ice deposit encircling the planet at 60N. This may have been part of the ancient northern ice sheet or ocean. The heat from Elysium Mons here would have been melting part of the moving polar cap and the water flowed north to the main ocean or ice sheet. This THEMIS map should be looked at in conjunction with the previously mentioned mola_regional.pdf.

 

Figure 2 shows a map of these ice rich areas. To make them clearer in monochrome we have made the blue areas on the original appear white.

 

A is the approximate position of North polar Cap 2, where white ice deposits can be seen. This trail moves to the right down to C, and on the left edge of the map at J which would be North Polar Cap 3. North east of A there is a trail of ice (more clear in the original map) shown by B. This connects to the large ice deposit at H. In the center of the ice trail at B is Elysium Mons. This implies that the heat from Elysium Mons melted water here to make the runoff to H, and therefore that Elysium Mons was hot when the pole was at A. On the northern end of this trail is where Viking 2 landed, and also the best example of Martian spider ravines[32] [33]outside of the current South Pole. The large ice deposit at South Polar Cap 3 in Meridiani Planum is shown at I, and F an ice trail linking it to a northern ice sheet.

 

This is consistent with the motion of the pole described here. At E we see a large ice trail again, this time next to Olympus Mons and also east towards Pavonis Mons[34]. This implies some of the ice of North polar Cap 3 was melted by Olympus Mons and moved north to the large ice area at G. E is also the location of Amazonis and Arcadia Planitia which show signs of having been made smooth by water[35]. Photos M1900946 and M1901546 show many volcanoes. These probably formed partially or wholly in water. While this water may have come from melting ice it may indicate the area was covered with ice or water. Olympus Mons and Tharsis would have been still hot at this time, which helps to date these events.

Figure 3: the Northern lowlands

 

Figure 3 shows dark areas on the Martian surface around the area of H in Figure 2. This implies these dark areas may be associated with higher amounts of ice. The trails of ice leading to these dark areas imply there was liquid water, which implies some parts may have been a liquid ocean at this time.

Figure 4: Amazonis and Arcadia Planitia.

Figure 4 shows the dark areas coinciding with Amazonis and Arcadia Planitia.

 

Figure 5: Map of Martian Iron at mid-latitudes.

In Figure 5 a map of Iron on mars from the Odyssey Gamma Ray Spectrometer[36] is shown. Here we have made the red, high iron areas on the original map black to be seen more clearly. E corresponds to Amazonis Planitia as a high Iron area. This is also associated with darker soil, has many water and ice signs, and is associated with the ice trail going northwards. So it is likely then some of the Iron may have been leached from the ground by water melted by Olympus Mons from North polar Cap 2. G shows the northern ice sheet is also Iron rich and connected by water or ice trails.

F shows an iron rich area coinciding with an ice rich area. Between K and B there is a trail of Iron from Meridiani Planum, or South polar Cap 3 up to Elysium Mons. This implies again that water from the pole moved north and north east to the large ice areas at H. C shows a large Iron deposit at North polar Cap 3.

 

It would be difficult for this Iron to occur in these areas due to glaciation alone, so it is likely has some association with water. This then implies a long-term northern ocean and ice sheet at the time Olympus Mons, with heat provided along the major north-south faults by Elysium and other Mons, at the same time the Pole moved from Position 2 to 3. The Opportunity area also has high iron (Fe). We know this is due to pisolite. Hence, pisolite may have formed in at least some of these regions.

 

As the Polar Cap moved along the dichotomy boundary from 2 to 3, 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. Amazonis Planitia is thought to be flat from sedimentation or fluvial processes according to Head[37]. Fuller et al[38] believe the Alba Patera area was resurfaced volcanically and with fluvial sediments. A periodically higher obliquity may have also created a water flow.

 

There are visible water channels in Lunae Planum, Xanthe Terra, and Margaritifer Sinus, but these became less common as the Polar Cap moved eastwards. The edges of the (green) elevation in MOLA maps[39] along this path may indicate the edges of the permanent ice cap cutting a flat platform. The primary erosion may have been caused by ice. Thus, at this stage Martian temperatures and air pressure were possibly dropping after the Argyre impact.

 

The ice deposit at South Polar Cap 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 Polar Cap 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 Polar Cap where the ground slopes more. Note also how South Polar Cap 3 also has an ice path at approximately 345W connecting to the northern ice sheet or ocean. Water and ice signs can be seen in narrow angle images from Malin Space Science Systems, such as E0101857, E0300317, E0401351, E0401589, E0503396, E1600085, E1801705, E2001051, E2100663, and  E2301402.

 

These ice paths imply the terrain at the time was conducive for water to flow into the ice rich areas at 60N, which implies these ice rich areas were formed substantially from water runoff themselves. If they were solely formed from ice deposition there would be no need for them to connect in apparent water paths. Much of this water may have moved in subsurface aquifers, which would explain a lack of rivers connecting to the ice rich area. Much of the water or ice had to previously exist there for polar wander to occur. This can easily be tested by simulating different depths of ice to these lower areas, and seeing if it balances the planet sufficiently for the polar path shown here to occur.

North Polar Cap 3 includes the area around Gusev Crater and the Spirit Rover site. Pablo et al[40] examined Atlantis Basin on this previous Polar Cap and believe this contained an ancient paleolake. This is consistent with the idea of a Polar Cap here, the area becoming desiccated when the Polar Cap moved on. The heat sources may have been from Olympus Mons, which would have been active at the time from the Argyre impact. Spirit has found indications of repeated exposure to water[41] [42]as well as more hematite concretions.

 

Irwin et al[43] describe Ma’adim Vallis as one of the largest valleys on Mars, believed to have been carved from a large flood. This amount of water on North Polar Cap 3 fits in well with the water signs at South Polar Cap 3. Water from North polar Cap 3 may have moved northwards into Arcadia Planitia.

 

Thomas-Keptra et al[44] propose carbonate disks in ALH84001 may have formed in an area similar to conditions found by the Rover Opportunity, which would link possible life signs to these former poles.

 

This is also consistent with the idea of the water at the Rover Opportunity site being from polar ice. Leask et al[45] examine the Ravi Vallis and Aromatum Chaos areas and calculate the amount of water that would have been involved. This would be the western edge of South Polar Cap 3 and also represent an area the Polar Cap moved over.

 

Coleman[46] also examined this area and believes an ice covered lake in Ganges Chasma recharged the aquifer source. This is also consistent with the ice and water coming from South Polar Cap 3. Woodworth-Lynas and Guigne[47] examine the Kasei Valles area and believe water here was covered by ice floes. This is on the western edge of South Polar Cap 3 and again implies large amounts of water connected with the areas examined by Opportunity. The results of Holden Crater, Aromatum Chaos and Kasei Valles imply the climate was warmer at one stage for South Polar Cap 3, perhaps from increased obliquity[48].

 

Barlow and Dohm[49] examine Arabia Terra which is also on the edge of South Polar Cap 3 and conclude a subsurface reservoir of ice and liquid water existed here. Dohm et al[50] also indicate the magnetic field may have been waning, consistent with the idea of the Hellas impact later attenuating the magnetic field of Mars.

 

Arkani-Hamed and Boutin[51] plotted magnetic poles which agree reasonably well with the movement of the Polar Cap along the dichotomy boundary. The movement is roughly cycloidal, and from this it may be possible to calculate how long it took the Polar Cap to move from South Polar Cap 2 to 3. This assumes the magnetic Polar Cap may tend to move around a given rotational Polar Cap position.

 

South Polar Cap 3  contains an area called the “Arabian Water-Rich Spot” with 16% water (Mitrofanov et al[52]). Dalton et al[53] also found evidence of water accumulation in the Flaugergues drainage divide, which is also on South Polar Cap 3.

 

In each case, rift-like fault systems and hence lakes were all adjacent to old polar caps. The valleys were then modified due to sublimation of the icecaps and fluvial activity obscuring much of the faulting (as with Chasma Australe).

 

If the degassing has a volcanic relationship as implied by the polar-fault relationships, then SO2 may the major gas released with the CO2 component being minor, related only to initial defrosting. This seasonal defrosting would open pathways allowing degassing to occur.

 

The high iron and the sulfur content would thus result from volcanic degassing. The Opportunity area is bounded by rift-like faults both sides, and these look like they controlled the lake. The same Fe and Sulfur relationships occur at Viking 2 (Utopia Planitia). In each case, rift-fault systems and hence lakes were all adjacent to old polar caps.

 

In the Opportunity region, the pisolites (blue berries) form in two ways. The first is by in situ replacement, possibly of titanium-rich minerals by a lateralization-like process due to surface water. Other pisolite overlay the Opportunity lake sediments. This may have formed by shedding from an old iron deposit or may have formed like a bog iron ore, after the polar cap moved. There is strong evidence[54] at Opportunity that Meridiani Planum was wet and hospitable for life. The water would likely be from the polar cap and implying an environment hospitable to life along the whole polar path.

 

Siltstones may have formed in lakes and oceans adjacent to polar caps. Some of these may have been carbonate rich (perhaps varves) at the time. Thus, the icecap formed, then the rift valleys formed, degassing and volcanism followed. The lakes may have existed in equilibrium with the icecaps so a stable hydrological system must have existed, at least near this polar pair.

 

Many of the rifts and major normal and strike slip faults of mars occur adjacent to the polar caps. Thus, the crust has preferentially fractured in polar regions. Degassing would occur due to increased geothermal activity near hot spots or fractures in the mars crust.

 

The gases given off would be: CH4, SO2, SO3, CO, CO2, H2O.

Some of the minerals formed due to hydrothermal activity would be: FeS, CuFeS, CuSO4.

SO2 + 2H2O => H2SO4 + H2

 

H2SO4 (sulfur) + CaCO3 (Limestone/calcium-rich silts) => CaSO4 (gypsum) + H2O + CO2  

The rocks at the Opportunity site indicate that the water then eroded the gypsum crystals. The pisolites overlay the lake sediments, and either formed during or most probably after the degassing event . The gypsum in the lake sediment must therefore either be due to the lakes/oceans drying up, or since the crystals crosscut the bedding may well even be related to the degassing.  

 

CaSO4 (gypsum) + SiO2 + H2O => Mud

 

In arctic conditions mud may not always form. The result may be very fine silt, which would mix with or cover any near surface ice. If the temperature were to increase the ice just below the surface melt and the material would flow to create the mud-like surface features we see at Opportunity. Even olivine would erode to fine dust particles. In addition, any original pyrite related to hydrothermal activity would eventually weather due to the existence of water.

2FeS (pyrite) +  3H2O =>   Fe2O3 (pisolite) + 2H2S (rotten egg gas) + 1/2H2           

 

The water would most likely then react to form sulfates or revert to ice and be covered by or mixed with dust.

 

Astrobiology

 

It has been openly speculated at the recent Rover Press Conferences about fossils[55] possibly being found at the Rover sites, particularly at Meridiani. Also there have been some objects found which some believe look like fossils. We will then examine the astrobiological implications of this polar path.

 

The polar movement from Pole 2 to pole 3 as shown is accompanied by regular discharges or water, flooding, and hematite deposits. Hematite[56] has been found in the area of 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[57] which is consistent with the Polar Cap moving and exposing this area. According to Hynek Aram Chaos and Valles Marineris[58] [59] also have hematite deposits, which is consistent with the path of the moving Polar Cap from South Polar Cap 2 to 3 giving water to create hematite. Hematite has been found by Spirit at Gusev Crater on North Polar Cap 3. Catling and McKay[60] discuss possible biological aspects of hematite deposits. Cockell[61] shows that life could survive under snow, which would protect from UV rays and still allow photosynthesis.

 

Hynek et al[62] say the erosion from water in Margaritifer Sinus lasted up to several hundred million years. If the whole polar wander path from Margaritifer Sinus to Meridiani Planum lasted only this long then it implies a habitable area may then have existed on Mars for long enough for life forms to have evolved in comparable time scales and environments as on Earth. Even in Margaritifer Sinus it may have been wet enough for long enough for life to evolve substantially. Life could have stayed close enough to the volcanoes for warmth, and the polar path implies at least Tharsis was hot for several hundred million years or more.

 

Opportunity[63] has found a volcanic rock almost identical spectrographically to the Shergotty meteorite found on Earth. If transfers of material were happening when Meridiani was a pole then it implies life from Earth (or vice versa) may have been introduced by the same mechanism along this polar wander path.

 

Several objects in particular seen at the Opportunity site seem to have a resemblance to fossil shapes, such as crinoids. The fossil shapes  may be also explained by vughs forming during lateritization - but since even skeptics agree they look like fossils, more
work is required to test this hypothesis.

 

Ausich et al[64] in their Figure 5 shows some shapes which can be compared to Figures 6 and 7 in this paper. Aronson and Blake[65] show similar shapes in Polychaetes. Radwanska and Radwanski[66] show more similar examples.

 

Figure 6[67]:

 

 

Figure 7[68]: The top of the fossil like shape appears to be beginning to branch in two. There appears to also be a tail like shape.

 

Schelble et al[69] discuss biological material often found associated with hematite, similar to shapes seen by the Opportunity Rover. Figure 8[70] shows a tubular shape reminiscent of a fossil or cryptobiotic soil crusts.