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
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”
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
Margaritifer Sinus contains remnant high valley densities, which is consistent with a moving pole and ice melting. This area was resurfaced several times,
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
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
drainage system is particularly extensive. Therefore, according to Grant, groundwater discharge
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
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 also
examine the area and how it connects the Argyre Basin
to the northern channels. Williams et al
report on fans in Xanthe Terra, along the path of the Polar Cap.
Hynek et al
suggest that the
fluvial resurfacing in this area lasted for a period of some several hundred million years. A
combination of rainfall and sapping
appear likely, so lakes may well
have formed. Polar wander may link the two main theories of
precipitation and sapping, hence explaining the extensive valley networks.
According to Nelson ice may have periodically melted. An
examination of Margaritifer
Sinus, by Philips et al
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
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
there. 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 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). Interestingly this would
have resulted from a
probable impact basin that formed a catastrophic outflow.
Nelson and Greeley
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. 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
see evidence of fluvial flows associated with Elysium Mons and lava flows in
the area, and rootless cones
also indicate ice in the area.
The new Odyssey results of subsurface
ice
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
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
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 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
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 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.
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.
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
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.
Fuller et al 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
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
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
as
well as more hematite concretions.
Irwin et al
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
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
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
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
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.
Barlow and Dohm
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
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
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). Dalton et al
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 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
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
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 which
is consistent with the Polar Cap 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
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
discuss possible biological aspects of hematite deposits. Cockell
shows that life could survive under snow, which would protect from UV rays and
still allow photosynthesis.
Hynek et al
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 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
in their Figure 5 shows some shapes which can be compared to Figures 6 and 7 in
this paper. Aronson and Blake
show similar shapes in Polychaetes. Radwanska and Radwanski
show more similar examples.
Figure 6:
Figure 7: 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
discuss biological material often found associated with hematite, similar to shapes
seen by the Opportunity Rover. Figure 8
shows a tubular shape reminiscent of a fossil or cryptobiotic soil crusts.
Figure 8
Krasnopolsky et al
have detected methane in the Martian atmosphere which they believe is coming
from the equatorial regions, which is consistent with this polar wander path.
Vittorio Formisano
has also found methane, at 10.5 parts per billion. Mumma et al
also found methane. On Earth methane is usually associated with biological
activity.
Conclusions
Geology along the polar path
suggested by Sprenke and Baker is consistent with polar ice and water. This
section of the polar path would have been initiated by the rise of Tharsis, and
as Tharsis moved to the Equator it forced the eventual South Pole eastward from
Solis Planum to Meridiani Planum.
Signs of water, ice erosion,
and hematite follow the polar wander path. Since the Opportunity Rover detected
a potentially habitable environment, this may have persisted during the entire polar
wander from Solis Planum and perhaps even earlier.
Estimates of the time taken to
make this polar path are consistent with the time needed for substantial
evolution to have taken place in Earth’s early history. If life existed on Mars
at the start of this path, then it is possible a habitable zone existed for
most of not all of this time.
Earlier than this an ice sheet
and ocean would have occupied parts of the Northern
Lowlands, in a shape consistent with water flows from the heat
around Olympus Mons and Elysium Mons. Water near
the heat from these volcanoes would be another potentially habitable zone for
as long as they supplied a heat source.
Objects have been found at the
Opportunity site with shapes similar to
fossils. Methane emissions from the equatorial regions could be signs of past
or present life. The polar wander path links a large volume of geological data
suggesting that liquid water and the prerequisites for life did exist on Mars
and over a substantial period in time. Thus, if life is not detected it may be
a function of the measurement methods used rather than life not having existed.
Future missions to mars need to be designed to help answer this more
substantively.
K. F. Sprenke and L. L. Baker (2000) “POLAR WANDERING ON MARS?” LPSC XXXI 1930.pdf
J. A. Grant (2001) “Valley Evolution in
Margaritifer Sinus, Mars” LPSC XXXII
1226.pdf.
“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].”
Ibid.
“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 [11] 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
[11]. 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.
“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.”
John A. Grant
(2001) “DRAINAGE EVOLUTION IN
MARGARITIFER SINUS, MARS”
Paper No. 132-0 GSA Annual Meeting, Boston, Massachusetts
“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.”
March 9, 2000. Goddard Space Flight Centre
“View inside Mars reveals rapid cooling and buried channels” Top Story.
Available online at http://www.gsfc.nasa.gov/topstory/20000309mars.html
“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.”
“Introduction:
The recent discovery of a distributary fan in a large crater
northeast of Holden by Malin
and
Edgett has been presented as evidence for persistent flow of water on Mars [1].
With at least three
separate
depositional lobes and a clearly layered structure, this feature is so far
unique among sedimentary
structures
on Mars. This fan has been deposited by fluvial processes, and then
subsequently eroded back
from
its original extent. This process has left behind an inverted topography, with
the floors of former channels standing above the surrounding terrain. Several
of the remnant channels in this formation appear to display meandering curves,
which is the strongest evidence for a steady supply of water at this location.
Further,
persistent flow raises the possibility that this feature was, at one time, a
lacustrine delta.”
“Introduction:
In recent years, the Mars Global Surveyor (MGS) Mars Orbiter
Camera (MOC)
investigation
has largely focused on NASA’s Mars Exploration Program “Follow the Water”
theme. We report here on MOC narrow angle (NA) images obtained in 2003
following observations from 1999 that show a specific, un-named, ~60
km-diameter impact crater at an equatorial latitude (7.6oN, 33.0oW) that
exhibits well-preserved landforms similar in planimetric form and morphology to
alluvial fans of arid environments such as the Mojave Desert of southern
California. The principal question is whether these fans represent the products
of water and gravity-driven alluvial sedimentation. The landforms in the Xanthe
Terra crater are unique
among
MOC images of martian impact craters, with the exception of some features in
middle latitude Hale Crater and its central peak (35.9°S, 36.6°W). The purpose
of this paper is to present an initial, brief description of these landforms
and explore their implications.
Some of the channels display branching
networks proximal to the fan (Fig. 3). The channel networks display a
third-order topology using Horton’s ordering scheme. First-order tributaries of
the channels that feed the fans extend to the crest of local topographic highs.
Locally, the density of channels (total channel length per area of network) is
extremely high (preliminary value >500 km-1), comparable to terrestrial
values for much larger scale rivers in humid environments with highly erodable
substrates. In areas of high channel density, channels are visible to the
resolution limit of the MOC NA images.”
B. M. Hynek and R. J. Phillips (2001)
“Evidence for extensive denudation of the Martian highlands” Geology, 29,
407-410.
“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.”
Ibid.
“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).”
http://ltpwww.gsfc.nasa.gov/tharsis/hynek.erosion.pdf
Ibid.
“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).”
B.
Moomaw (2001) “Mars: A World of Varied
Catastrophes” MARSDAILY May
1, 2001 available online at http://www.spacedaily.com/news/lunarplanet-2001-01a2.html
“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”
R. J. Phillips et al (2001) “Ancient
Geodynamics and Global-Scale Hydrology on Mars”
SCIENCE VOL 291 30 MARCH 2001
“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).”
H. Frey
(2001) Geodynamics “2001 The Year in Review” Annual Report of the Geodynamics
Branch, Goddard Space Flight
Center.
“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.”
B. Murray [1999] “PALEOLAKE DEPOSITS IN
CENTRAL VALLES MARINERIS: A UNIQUE OPPORTUNITY FOR 2001” Second Mars Surveyor
landing site Workshop.
“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.”
Ibid
“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.”
A.P.
Rossi et al (1999) “[46.03] Flow-like
features in Valles Marineris, Mars: Possible ice-driven creep processes” 31st
Annual Meeting of the DPS, October 1999 Session 46. Mars Surface: Evidence of
Change Posters .
“Recent high resolution MOC images have
revealed the presence of deformed impact craters on flow-like features
characterized by narrow bands of alternating light and dark material on the
walls of Valles Marineris. The maximum crater elongations are consistent with
the flow directions. Moreover the directions of these flows follow the
topography downslope. In some cases, the flows emanate from cirque-like
depressions, and the flows are divided by sharp ridges similar to arête. These
landforms have resemblance to (1) alpine-type glacier morphology, including
cirques, arêtes, and glaciers containing medial moraines; and (2) Grand
Canyon-type sapping and mass wasting features. Certain aspects of the features
in Valles Marineris seem more consistent with the first hypothesis involving a
viscous rheology of the flows driven by ice-assisted creep processes. This
hypothesis includes direct analogies to glaciers and rock glaciers. In the case
of rock glaciers, flow is produced by freeze-thaw and by internal deformation
of ice cores or lenses, whereas in the case of glaciers, movement occurs by
internal deformation plus basal sliding in some cases where the glacier is
melted at its bed. The amounts and roles of ice in the genesis of the Martian
glacier-type landforms in Valles Marineris are not clear at this point. The
population density of undeformed fresh impact craters on these flows appears to
be low compared with the surrounding plateau areas. This may indicate
relatively recent ages of the flow processes.”
R.
Greeley and R. Kuzmin (1999) “SHALBATANA VALLIS: A POTENTIAL SITE FOR ANCIENT
GROUND WATER” 2nd Mars
Surveyor landing site workshop, SUNY/Buffalo,
43-44
“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 [7].”
D.M. Nelson and R. Greeley (1998) “XANTHE
TERRA OUTFLOW CHANNEL GEOLOGY AT THE MARS PATHFINDER LANDING SITE” LPSC XXIX 1158.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.”
Ibid.
“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 [7], 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.”
P. D. Lanagan et al (2001) “GEOMORPHOLOGIC
MAPPING OF CERBERUS PLAINS, MARS” LPSC XXXII 2077.pdf
“Fluvial features in the Cerberus plains cut into and are
covered by lava flows [2]. MOC images, which show streamlined islands and
longitudinal grooves, and MOLA topography suggest that water that carved the more
recent of these channels originated from Cerberus Rupes or in regions of ground
collapse highland rem-nants north of Cerberus Rupes, ran south into the
Cer-berus plains, and finally emptied into Amazonis Plani-tia via the Marte
Valles outflow channels [1].”
Lanagan et al (2001) Rootless cones on
Mars indicating the presence of shallow equatorial ground ice in recent times”,
Geophysical Research Letters, vol. 28, p. 2365-2368.
“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 Hawai`i) 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.”
M. Caplinger
February (1994) “Determining the age of surfaces on Mars” Malin Space
Science Systems, Available online at:
D. E. Smith and M. T. Zuber (2004)
“Gravitational effects of flooding and filling of impact basins on Mars” LPSC
XXXV 1923.pdf.
“Introduction.
The presence of large impact basins and the low northern
plains that might have contained ice or liquid water at an earlier stage of
Mars’ evolution suggests that the global gravity field could have been
different in the distant past than it is today. In addition, any significant
change in the distribution of mass affects the moments of inertia and
consequently and could conceivably change the position of the Polar Cap and the
length of day. Similar effects could have been produced by large erosional
processes, such as the removal of crustal material from the Arabia Terra region
and subsequent re-depostion in the Chryse region of the northern plains [1]. We
have endeavored to estimate the magnitudes of material that might have been
involved in these processes and their possible effect on the gravity and
dynamics of Mars. We have used present-day topography [2] and gravity field [3]
as a starting point, recognizing that both the result of the processes that we
are trying to study rather than the state at the times of interest.
Basin
Volumes. The largest volume (arbitrarily defined below zero
elevation) that could have been filled with H2O in the past is the northern
plains (Fig. 1a) , which occupy about 47% of the surface of the planet [2].
Because of its location, which is approximately symmetrical about the Polar
Cap, the additional mass associated with flooding contributes largely to the
zonal gravity field, particularly degrees 1, 2 and 3, with small changes to the
moments of inertia. (Note: we do not account for flexural effects.) Hellas (Fig. 1b) is the largest impact basin, and if
filled to the zero
elevation
level would only hold about 10% of the volume of the northern plains. But
because of its location at 30 to 50S, 50 to 90oE, it has the potential to have
a larger effect on the moments. If suddenly filled today it would want to move
toward the equator and because it is almost antipodal position to Tharsis it
would move Tharsis southward [cf. 4]. The second largest impact basin
was probably Utopia [5, 6] but today it is filled with sediments and volcanics
[7], thus making the basin much shallower than it was originally. It appears to
have been a Hellas sized basin and therefore
might have been a significant contributor to global-scale mass re-distribution.
Argyre, in comparison to Hellas, has only about 10% of the volume of Hellas as measured by today’s topography, and has a relatively minor effect on the
global mass redistribution.”
“Discussion: Our results for Arabia and
Deu-teronilus shoreline present-day topography are some- what lower than those
obtained previously [7,8]. the Meridiani shoreline our result is clearly lower
than
that in [8], fundamentally due to
the fact that these authors use an excessively high value of 0 (with re-
spect to the global datum) for the
mean paleoshoreline elevation, whereas we use a mean elevation of −1.5 km
[17]. Elevational range and geologic relations along Ara-bia shoreline,
especially with respect to the Tharsis region, suggests that this is not a true
paleoshoreline [7,8]. This implies that volumes obtained for the Ara-bia
shoreline are likely not representative of any an-cient martian ocean.
Otherwise, elevations in the puta-tive Meridiani shoreline are roughly similar
to those of the Arabia shoreline in
northeast Arabia, Utopia (not taken into
account the Isidis basin), Elysium, and Amazonis regions. A paleoshoreline
through these Arabia shoreline portions and
the Meridiani shoreline would be a better candidate to represent a true ancient
oceanic limit [5,18]: areas, volumes, mean depths and GELs obtained here for
the Meridiani shoreline would be roughly valid for this possible
paleoshoreline.”
“Oddly enough, Viking 2 [137] landed [138] nearly in the middle of a sub polar area
that seems truly spider like [139]. Interestingly, some troughs were found
near Viking 2 [140]. While other explanations have been
suggested, the presence of the spiders nearby and their association with
sometimes polygonal ravines makes these troughs possibly spider ravines. These
"enigmatic troughs" [141] can be traced in a sequence of photos [142]. If they are spider ravines, it might
indicate that when the spiders seasonally dissipate, they might leave ravines
that are too shallow to see. There are also pits [143] in the area of unknown origin. In The
Martian Landscape , Figures 195 [144],199[145], and 200 [146] may also be troughs. Figures 290, 210 and
211 [147] show paler areas devoid of rocks, which may
be related to spiders. Of course, there are many other explanations but the
proximity to the spiders makes these interesting. In imagery of the landing
site [148], spider branches are 1-3 pixels wide where
a pixel's width [149] is 9.46 meters [150]. Since spiders typically have a paler
albedo and a comparable branch width to these pale patches, it is possible that
they might be spider remnants.”
“Introduction: Each of the three Tharsis
Montes volcanoes on Mars has unusual fan-shaped
deposits
located exclusively to the
west-northwest of each shield. The fan-shaped
deposits of the Tharsis Montes
generally share three major facies:
1) a ridged facies, 2) a knobby facies, and 3) a smooth facies. Any ex-
planation for the origin of the fan-shaped deposits must take into account both the similarities and
differences in their morphologies, their approximately similar Amazonian age,
and the fact that all three occur on the west-northwestern sides of the
volcanoes [1]. Based on Viking Orbiter data, several
models have been pro- posed for their formation, including massive landslides
[2], glacial processes [3,4,5,6] and pyroclastic
flows [6]. We support a glacial origin for
the fan-shaped deposits and refine the
previous models using new data from both the Earth and Mars. Based on Viking Or-biter data, Williams [3] and Lucchitta [4]
suggested that the fan-shaped deposits were the result of
the deposition of moraines due to recession of local ice caps that formed on
the volcanoes from mixtures of emanated volatiles and erupted ash [4]. Scott et
al. [6] suggest an explanation combining glacial
and volcanic processes
…
We interpret these ridges as drop
moraines formed at the margins of a retreating cold-based glacier [7].
The fact that these ridges can be
seen in the proximal regions of the Pavonis fan-shaped deposit suggests that at least one major phase of retreat and
deposition oc-curred. The ridges are superposed on underlying to-pography,
including a lobate lava flow to the west, and are not deflected by obstacles.
The fact that the ridged facies is observed up to elevations of 9.2 km above
Mars datum on the northern flanks of Pavonis
suggests that a large glacier would have covered a significant portion of the
flanks of the shield.”
E.R. Fuller and J.W. Head III (2002) “GEOLOGIC HISTORY OF THE SMOOTHEST PLAINS ON MARS
(AMAZONIS PLANITIA) AND ASTROBIOLOGICAL IMPLICATIONS” LPSCXXXIII 1539.pdf
“The
cryosphere, a frozen layer of ice and regolith, has been acting as a global
aquitard to the groundwater system below [e.g., 9]. Once the cryosphere is
breached, the water, under hydrostatic pressure, emerges with very high flow
rates, and continues flowing until pressure equilibrium is reached. This water
flowed through Marte Vallis, eroding channels and debouching into Amazonis
Planitia. This catastrophic outflow was shortly followed by lava outflow; the
magma flowed through the fracture and released flood lavas onto the surface.
This lava followed the path of the water, re-surfacing Marte Vallis and pouring
into Amazonis
Planitia. As it flowed over the
water-saturated surface, the phreatomagmatic interactions created rootless cone
structures [see also discussion in 10]. Astrobiological implications:
The lava flows associated with the emplacement of these plains have been dated
as extremely young geologically (less than 10 million years old [11]). If
fossil or extant life existed at depth in the subsurface groundwater system at this
time (a troglodytic fauna), it is highly likely that they would be among the
material erupted to the surface, and washed down into Elysium Planitia and Amazonis
Planitia. The fate of such effluents under current martian conditions has
recently been modeled [12] and it has been shown that standing bodies of water
at this scale would quickly freeze over and sublimate, leaving a sedimentary
sublimation residue. Thus, Elysium and Amazonis Planitiae would be excellent
locations to sample recently emplaced freeze- dried troglodytic faunal remains.”
O. Aharonson et al (1998) “Mars: Northern hemisphere slopes and slope
distributions” GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 24, PAGES 4413-4416,
DECEMBER 15, 1998.
“Characterization of Martian surface slopes from the aerobreaking hiatus
phase of the MGS mission provided several insights. Regional slopes across
prominent canyons measured on a 10-km baseline range from 0 − 5_ for
regions which have undergone mass wasting and collapse, up to approximately 30_ for less modi_ed scarps. The average slopes across
the dichotomy boundary are small, < 1_, but on a local
scale can execed 20_. The northern lowlands are found to be unusually
smooth and form a distinct statistical population. Other distinct populations
correspond to the rough highlands and the extremely smooth Amazonis Planitia
region. Amazonis is markedly smoother than any other large scale surface
observed onMars, than volcanic plains on both the Moon and Venus, and than an
example of desert terrain on the Earth. Its statistical properties resemble
most closely certain terrestrial depositional environments including
oceanic abyssal plains and
sedimentary basins. Given previously hypothesized scenarios for Mars'
geological past [Carr, 1981], the evidence so far may
be consistent with an origin for Amazonis in which extensive aeolian deposition
follows a volcanic resurfacing event. Also possible is a modicational history
in which water provides a sedimentary environment capable of efficiently
smoothing meter scale topography.”
E. R. Fuller and J. W. Head III (2002)
“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.
“[9] Parker et al. [1993] drew Contact 2, one of two
interpreted shorelines for their proposed Hesperian northern ocean, near the
margins of the central smooth unit of Amazonis Planitia. Head et al. [1999], using MOLA data,
assessed the elevation of the two contacts, and found that Contact 1 deviated
substantially from an equipotential line, but that Contact 2 was much closer to
being level, with a mean elevation of 3760 m below the Martian datum. Figure 5e
shows the trace of the _3760
m contour through the
Amazonis Planitia region.
…
[10] Morris and Tanaka [1994] mapped the eastern
edge of Amazonis Planitia in their analysis of the Olympus Mons region. They
identified two plains subunits of the Arcadia Formation (Figure 2): Aa1 and Aa2, both volcanic plains mantled by aeolian
deposits. They also present evidence that the age of mapped volcanic units
associated with Olympus Mons span the Middle to Late Amazonian, and that if the
aureole deposits
represent the collapse of a proto-Olympus Mons
edifice, then extrusive activity must have extended back to the Late Hesperian.
On the basis of their mapping, they favor a landsliding and gravity-spreading
mechanism [see also Tanaka, 1985; Francis and Wadge, 1983], but point out
that this requires a lubricant such as water or ice. They further point out a
weakness of their hypothesis: ‘‘if a huge,
proto-Olympus Mons had formed (necessary
for the landsliding and gravity-spreading mechanisms), extant lava flow fields
beyond the aureoles might be expected, but they are absent’’ [Morris and Tanaka, 1994, p. 15].
…
Its smoothness is
comparable only with Earth regions shaped by long-term aqueous deposition, such
as ocean floors and the North American Great Plains (the former location of an
epeiric sea) [Aharonson
et al.,
1998]. Re-examination of Pass 31 shows that the smoothest region within the
several thousand
kilometer-long track
corresponds precisely with the central smooth unit of Amazonis Planitia
identified in this study (Figure 7).”
“The subsequent evolution of Atlantis Basin
is closely related to the evolution of Eridania Lake.
The
desiccation
of Eridania Lake, probably during the Late Noachian
[5], might have predated the existence of a series of reduced and interconnected
lakes in the area, in which Atlantis might have been included. In this
work
we propose the name Atlantis Lake for the lake formed inside this basin
and originated in the decrease
of
the water level of the Eridania
Lake. Water probably
flowed in the area from the South, initially
draining
to Southwest, but later forming an endorreic basin until its complete
desiccation. In relation with
this
evolutionary sequence, the presence of ‘mesas’ in the basin edges (Fig. 1-f)
have been interpreted as
sedimentary
materials deposited in the floor of the ancient Eridania Lake,
and subsequently eroded. This
interpretation,
together with the presence of relatively recent collapse areas (Fig. 1-g) and
mud-flow deposits (Fig. 1-h) around the Atlantis Chaos terrain, indicate the
existence of liquid water in the recent past. The appearance of linear
structures in the interior of Atlantis basin has been interpreted as indicative
of possible ancient dike systems [8], whose new activation would explain the
existence of the
subsidence
zones and the mud-flow deposits by the fusion of the permafrost. Equally, the
presence of
gullies
(Fig. 1-i) in several closed basins near to Atlantis Basin
(as Gorgonum Chaos [9]), makes
feasible
the existence of recent liquid water under the surface [10] [11] [12] [13].
Astrobiological
interest: The intense volcanic and tectonic activities, and the
presence of possible
dikes
in the area, as well as the relation of Atlantis with the former wide Eridania Lake, the gullies, and
the
sedimentary deposits, all highlight the astrobiological interest of Atlantis. A
heat source
related
to tectonovolcanic activity and flowing and ponded water are both hypothesized
to have been
present in the basin in different periods
of the Martian history, perhaps until recent times (Late Amazonian).”
R. P. Irwin III and T. A. Maxwell (2004)
LPSC XXXV 1852.pdf.
“Introduction:
At 900 km long, 8−15 km wide and up to 2,100 m deep,
Ma’adim Vallis is one of the largest valleys in the Martian highlands. The
valley descends northward and terminates at the landing site for the Spirit
Mars Exploration Rover at Gusev Crater, which acted as a detention pond or
terminal basin for Ma’adim flows [1]. Previously we identified the valley head
at the breached drainage divide of an enclosed basin in the mid-latitude
highlands. Along with characteristics of the head basin, this feature suggested
that the valley was carved primarily during a single paleolake overflow at the
Noachian/Hesperian boundary [2] (~3.7 Ga [3]). Earlier work had suggested that
Ma’adim Vallis was carved over a prolonged period up to 1.8 Ga by episodic
groundwater-fed flows [4−10]. Here we investigate the valley’s longevity
using crater counting, topography, and flow hydraulics. These
analyses
provide quantitative support for development of the valley during a brief
overflow, followed by a
geologically brief period of tributary
development.”
“Introduction Dated at ~3.9 billion
years of age, carbonate disks [1], found within fractures of the host rock of
Martian meteorite ALH84001, have been interpreted as secondary minerals that
formed at low temperature [e.g., 2] in an aqueous medium [e.g., 3].
Heterogeneously distributed within these disks are magnetite nanocrystals that
are of Martian origin. Approximately one quarter of these magnetites have
morphological and chemical similarities to magnetite particles produced by
magnetotactic bacteria strain MV-1 [4], which are
ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite
particles are not known or expected to be produced by abiotic means either
through geological processes or synthetically in the laboratory. The remaining
three-quarters of the ALH84001 magnetites are likely products of multiple
processes including, but not limited to, precipitation from a hydrothermal
fluid, thermal decomposition of the carbonate matrix in which they are
embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We
have proposed that the origins of magnetites in ALH84001 can be best explained
as the products of multiple processes, one of which is biological.
“Summary: The
Aromatum Chaos depression- Ravi Vallis outflow channel system is sufficiently
simple
that water flow rate and volume estimates can be made that throw light on
processes operating to
form
the Aromatum and Ravi features. Typical
discharge rates through Ravi Vallis are estimated at 3
x
106 m3 s-1. By assuming a high sediment load in the water we find a minimum
duration of ~2 months.
Too
much water flowed in the channel to be explained by cryosphere melting alone,
and drainage
of
a local aquifer system delineated by intrusions is clearly implicated.
Aromatum
Chaos: The main Aromatum Chaos depression is a truncated triangle
~92 km long and an
average
of 30 km wide (Fig. 1). Its interior consists mainly of a mass of
blocky-chaotic terrain, with
blocks
generally becoming progressively smaller towards its Eastern end. Some larger
blocks at the
Western
end show some evidence of rotational slumping and also appear to be less
eroded, having
flat
tops showing a rather angular connection between the flat top and the walls.
The edges of
Aromatum
Chaos show strong evidence of local structural control and so, in an attempt to
look for
similar
control of the interior, we examined all MOLA profiles crossing the interior,
and found 30
profiles
which collectively crossed the tops of 20 blocks. From these we measured the
absolute heights
(relative
to Mars datum) of the tops of the blocks and their depths below the rim of the
depression. The
tops
of blocks lie between 1,008 m and 2,361 m below the rim and show no systematic
correlation
with
depth below rim or height above floor, suggesting piecemeal collapse rather
than a structural
control on their subsidence.”
N. Coleman (2004) LPSC XXXV1299.pdf.
“Floodwater
Sources: Confined groundwater was the apparent source for the initial
outflows. If this were the only source the flow could not have been sustained
because confined aquifers, once released, tend to depressurize rapidly. The
unconfined dewatering of an aquifer takes much longer. In addition, the
presence of an ice-covered lake in ancestral Ganges Chasma would
have
provided a substantial reservoir to recharge the aquifer source for both Ravi
V. [7] and Shalbatana V. [7, 10], permitting outflows over an extended period.
If the flows were concurrent, then the flooding occurred in mid- to
upper-Hesperian because Shalbatana V. incised
ridged plains material of lower Hesperian
age [11].”
C. Woodworth-Lynas and J. Guigne (2004)
“Extent of floating ice in an ancient Echus Chasma/Kasei Valles valley system,
Mars” LPSC XXXV 1571.pdf.
“Introduction:
From images of the Echus Chasma/Kasei Valles valley system
we present further, new observations of surficial Martian features that are
interpreted to be the result of interactions between the keels of flat-bottomed
floating ice floes with a submerged sediment [1,2]. These features are proxy
indicators of three basic environmental conditions: the former presence of a
water body; the water body was seasonally, or perhaps permanently, covered by
ice floes; the water area was large enough for winds, currents or both to drive
the floes forward during ice/lakebed interaction. We also present an analysis
of shorelines. These observations are made from analyses of Mars Global
Surveyor Mars Orbiter Camera (MOC) images. In places we have observed several,
closely-spaced, terraces
interpreted to be shorelines preserved at
different elevations along the margins of the valley system. We use the
geographic distribution of the floating ice-related features and shoreline
terraces to define the limits of floating ice in the valley system. We compare
the shoreline boundaries with equipotential (waterline) surfaces using Mars
Orbital Laser Altimeter (MOLA) data, and estimate the volume of water and
floating ice that occupied the valley system.”
T. Nakamura and E.
Tajika (2002) “Evolution of the climate system of Mars: effects of
obliquity change” LPSC XXXII 1057.pdf.
“The obliquity change
could cause a climate jump in the Martian climate
system on short timescale. Figure
2 shows the annual mean atmospheric
pressure as a function of the obliquity. The
present solar constant
and 2.0 bar of the total amount of
CO2 in the system are assumed for a nominal example. There are two
branches of the solution. One is a
“cold” residual-cap solution branch, and the other is a “warm” no-ice-cap
solution branch. It is noted that
the residual-cap solution branch disappears in higher obliquity
region. On
the other hand, the no-ice-cap
solution branch does not exist in lower obliquity
region. Therefore, climate
jumps should occur at the ends of
two branches. Assuming the state I
in Figure 2 as an initial state, for
example, when the obliquity increases, the state should change
to be the state II. If the obliquity continues to increase, a climate
jump will occur from the state II
to III to reach the state IV. This climate
jump results in a drastic increase in the atmospheric CO2 pressure, thus
warming. On the other hand, starting from the state is IV, if the obliquity decreases,
the state changes from the state IV
to I via a climate jump from the state V
to VI. In this case, the climate jump results in a decrease in the atmospheric pressure,
thus cooling. It is, therefore, suggested that the Martian climate could have dramatically changed repeatedly in short-term
cycles during the Martian history.”
“Discussion:
Crater morphologic and central pit data suggest that Arabia
hosts a subsurface volatile rich
reservoir
of ice and possibly liquid water. The crater data are just one indicator of the
uniqueness of
Arabia Terra. The combined
stratigraphic, topographic, structural, crater, geomorphic, geophysical,
elemental, and thermophysical signatures
suggest that Arabia is unusual compared to
other highlands regions [1]. GRS neutron spectrometer data reveal Arabia to be one of the most H2O-rich areas in the
equatorial region of Mars [10, 11]. The correlation of this region with crater
indicators of subsurface volatiles suggest that volatiles exist over a range of
depths in this region, from less than a meter (GRS/NS analysis) to over 2 km
depth (based on crater depth-diameter analysis). The existence of ejecta and central
pit features over a range of crater preservation ages indicates that this
volatile reservoir has existed for a substantial amount of Martian history,
perhaps extending back into the Noachian based on the ages of ejecta craters
[12].”
J. M. Dohm et al (2004) “Ancient giant
basin/aquifer system in the Arabia Region, Mars”. LPSC XXXV 1209.pdf.
“Magnetic anomalies are
observed in this region, although the magnitude is diminished relative to the
anomalies in the Terra Cimmeria region [1,2]. The impact would have erased any preexisting magnetic anomalies in
the crust as is seen with Hellas and Argyre.
If, however, the impact occurred when the dynamo was active, the crust would
have a chance to reacquire magnetization. The diminished intensity could indicate
that the dynamo was active but in a waning stage. On the other hand, the
reduction in magnetic signals may be the result of deep burial by basin infill.
Although there is no geophysical manifestation of a large buried impact basin
in the gravity or magnetic data (e.g., circular positive mascons as noted for
Argyre, but subdued for Hellas), the extreme
age of the event may preclude any detectable geophysical signature and may in
fact explain the uniform appearance of the gravity.”
J. Arkani-Hamed and D. Boutin (2003)
“Polar wander of Mars: Evidence from magnetic anomalies” Sixth International
Conference on Mars. 3051.pdf.
“Introduction: The polar wander of
Mars has been suggested by many investigators. The
quasi-circular surface morphology of the deposits
in the polar region detected by Mariner 9 mission led Murray and Malin [1973]
to suggest that the Martian rotation axis has wandered by 10-20 degrees in the
last ~100 Myr. Melosh [1980] gradually removed the mass of Tharsis bulge
while diagonalizing the moment of inertia
tensor of Mars, and showed that the Martian rotation
axis has displaced by about 25 degrees due
to the formation of the bulge. The similarity between
the deposits on Mesogaea, south of Olympus, and those in the polar region led Schultz and
Lutz
[1988] to suggest a polar path with a total
of 120 degree wandering. Long-term rotational dynamics of Mars was
theoretically investigated by Spada et al. [1996] through modeling Olympus mountain as a point mass, initially located at 45
degree latitude on the surface, and allowing the mass to reach the equator.
They considered a comprehensive suit of internal structure models of Mars with
mantle viscosity ranging from 1021 to 1023 and imposed the Murray and Malin's
constraint of 10-20 degree polar wander in the last 100 MYr. The authors
concluded that the mass will reach the equator within less than 2 Gyr., in a
much shorter time for low viscosity mantle models. It is also shown that a
thick elastic lithosphere atop a viscous mantle increases polar wander because
of elastically supporting the surface mass and allowing its greater influence
on the rotational dynamics of Mars [Willmann, 1984; Stiefelhagen, 2002]. The
Mars Global Surveyor magnetic data have provided new evidence for the polar
wander of Mars. Arkani-Hamed (2001a) estimated the paleomagnetic Polar Cap
positions of Mars through modeling 10 small and isolated magnetic anomalies.
Seven out of the 10 Polar Caps clustered within a radius of 30 degrees centered
at 25N, 225E. Hood and Zakharian (2001) modeled the source bodies of two
magnetic anomalies near the north Polar Cap. One of the anomalies was included
in the 10 anomalies modeled by Arkani-Hamed, and the Polar Cap positions of
this anomaly determined by the authors were very close. Assuming that the
diPolar Cap core field axis coincided with the rotation axis, the clustering of
the Polar Caps suggests that the rotation axis has wandered by about 65 degrees
since the magnetic source bodies were magnetized. This critical assumption that
links the diPolar Cap core field axis to the rotation axis presently holds for
both terrestrial planets with active core dynamo, Earth and Mercury, and
possibly for Earth throughout its history. We make the same assumption in this
paper.”
I.G. Mitrofanov et al (2004) “Arabia and Memonia equatorial regions with high content
of water: data from HEND/ODYSSEY” LPSC XXXV (2004) 1640.pdf.
“Results. The
consistency of HM and DLM with observational data was tested for the samples of
pixels for
Arabia and Memnonia. It was shown
that DLM model is better supported by the observational data for Arabia and Memnonia in comparison with HM. The best
fitting values of parameters down were used for estimation of water
content at these regions. It was shown (see [7]) that North Arabia
(0-45E, 0-30S) contains on average 9.0 wt% of
water under a dry layer with thickness of 26 g/cm2; the South Arabia
(0-45E, 0-20S) contains on average 10.0 wt% of
water under a dry layer with thickness of 32 g/cm2; the Memnonia
(180-200E, 0-25S) contains on average 9.0 wt%
of water under a dry layer with thickness of 29 g/cm2. One particular surface
element with coordinates (30E, 10N) has the smallest emission
of epithermal neutrons in the equatorial belt (Figure 2).The best fitting
subsurface parameters for this element correspond to 16 wt% water under a dry
layer with thickness 29 g/cm2 [7]. This estimate for the dry layer is
consistent with the average value found for the entire North
Arabia. Therefore, this result showing a high content of water at
this surface element is not produced by uncertainties in the model-dependent
data deconvolution. The value of 16 wt% corresponds to a real minimum in
epithermal neutron flux in Arabia. We name
this spot “Arabian Water-Rich
Spot”, or AWRS. It lies around an old eroded crater between craters Cassini and
Schiaparelli.”
J.B. Dalton et al (2004) “Search for
evaporate minerals in Flaugergues
Basin, Mars” LPSC XXXV
1869.pdf.
“the Flaugergues drainage
divide in the Noachis region of Mars (16.8 S, 340.8 W; [4]) indicates areas
of
water accumulation (Fig. 1). Putative paleolakes residing in craters (e.g.,
Gusev Crater, Schiaparelli)
have
already been examined for evidence of aqueous minerals. However, basin flow
models suggest that
craters
deeper than low-lying basins do not necessarily drain large areas. Raised
crater rims often
isolate
craters from their surroundings. The model has identified areas of water
accumulation fed by
large geographic areas which could produce
enhanced transport of aqueous materials. MOLA A shaded-relief map
constructed from MOLA data was used to assess the geomorphology of putative
paleolake basins. Many were found to exhibit smooth features suggestive of a
lake bottom.”
P.R. Christensen et al (2000) “THE
DISTRIBUTION OF CRYSTALLINE HEMATITE ON MARS FROM THE THERMAL EMISSION
SPECTROMETER: EVIDENCE FOR LIQUID WATER” Lunar and Planetary Science XXXI
1627.pdf.
“Crystalline hematite has been mapped over an area in
Sinus Meridiani approximately 500 km in longitude extending approximately 200
km in latitude [3]. 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.”
M.
D. Lane et al (2001) “UPDATE ON STUDIES OF THE
MARTIAN HEMATITE-RICH AREAS” LPSC XXXII 1984.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.”
L.R. Gaddis et al (2003) “MINERAL MAPPING IN VALLES MARINERIS,
MARS: A NEW APPROACH TO SPECTRAL DEMIXING OF TES DATA” LPSC XXXIV 1956.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
[18], but we see only (~8%) a small enrichment of red hematite in the possible
hydrothermal site in west Candor [14] (Fig. 6).”
F. S. Anderson et al (2003) “MINERALOGY OF
THE VALLES MARINERIS FROM TES AND THEMIS” Sixth International Conference on
Mars (2003) 3280.pdf.
“Our observations of hematite in the VM are similar to
those seen by Christensen et al., [37].”
“The Thermal Emission Spectrometer on NASA's Mars Global
Surveyor has detected deposits of crystalline hematite [1] in Sinus Meridiani,
Aram Chaos and Vallis Marineris. These appear to be similar to terrestrial iron
formations that formed in the Earth's Pre-cambrian oceans. The Sinus Meridiani
deposit
exceeds
~105km2 in
size, and consists of coarse-grained, grey, schistose hematite [2]. Its age is
~4Ga or older based on counts of exhumed fossil craters [3]. Terrestrial Banded
Iron Formations (BIFs) are laminated sediments deposited directly from
solution. Pathological cases of crystalline hematite are
particularly
characteristic of the Late Proterozoic. These are associated with glaciomarine
deposits and possibly formed when oceanic ice cover retreated. Iron oxides were
precipitated when ferrous iron reacted with dissolved O2.
There is no question that the oxygen in the late Proterozoic atmosphere
originated
from
photosynthetic organisms. Could iron formations that formed ~4 Ga ago on Mars
also be related to oxygenic photosynthesis?
On
early Mars several mechanisms could precipitate iron oxides from solution.
However, these processes all stoichiometrically require oxygen. There are only
two possibilities for an oxygen source: (1) Small quantities of oxygen were
slowly produced as hydrogen escaped to space and ferrous iron acted as a sink
for this oxygen over an extended timescale.
(2)
Early Mars had an oxygenic photosynthetic biosphere. Simple calculations
suggest that atmospheric oxygen was very scarce on a volcanically active early
Mars. The exposed deposits of hematite, if they are deep, would require
significant quantities of oxygen. Finally, although many of the findings
suggestive
of life in the ALH84001 meteorite have been disputed, the strongest piece of
evidence has always been magnetite crystals of biogenic shape. It is
interesting to note that magneto-tactic bacteria use magnetite for a specific
purpose: to move along a redox gradient away from a surface environment
dominated by oxygen.”
C.S Cockell (2003) “LIFE IN MARTIAN SNOWS
– MEASUREMENTS OF UV PROTECTION UNDER NATURAL ANTARCTIC SNOWS IN THE UVC (254
nm)” Third Mars Polar Science Conference
6125.pdf.
“Convolved with a simple Mars radiative
transfer model, the data suggests that under ~6 cm of Martian
snow, DNA-damage would be
reduced by an order of magnitude [2]. Under approximately 30 cm of snow,
DNA damage would be no
worse than that experienced at the surface of the Earth. Although we do not
know the exact
characteristics of Martian snows, these first-order data suggest that burial in
even modest coverings of Martian snows could allow for the long-term survival
(and if water if present, even growth) of contaminant microorganisms at the
Martian polar caps even under the extreme UV fluxes of clear Martian
skies. These coverings of
snow will also allow for enhanced preservation of organics against
UVdegradation. Intriguingly, at the depth at which DNA damage is reduced to
similar levels as those found on the surface of present-day Earth, light levels
in the photosynthetically active region (400 to 700 nm) are still two orders of
magnitude higher than the minimum required for photosynthesis, showing that
within snow-pack on planets lacking an ozone shield, including Mars, UV damage
can be mitigated, but light levels are still high enough for organisms that have
a requirement for exposure to light for their energy needs. Photosynthetic life
is not expected at the Martian poles, but the data reveal the apparently
favourable radiation environment for life within the polar caps.”
B.
M. Hynek and R. J. Phillips (2001) “Evidence for extensive denudation of the
Martian highlands” Geology, 29, 407-410.
“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.”
WILLIAM I. AUSICH, et al. J. Paleont., 76(6),
2002, pp. 975–992 Copyright q 2002, The Paleontological Society
“0022-3360/02/0076-975 “ORDOVICIAN [DOBROTIVIAN (LLANDEILLIAN STAGE) TO
ASHGILL] CRINOIDS (PHYLUM ECHINODERMATA) FROM THE MONTES DE TOLEDO AND SIERRA
MORENA, SPAIN WITH IMPLICATIONS FOR PALEOGEOGRAPHY OF PERI-GONDWANA”
R. B. ARONSON, AND D. B. BLAKE (2001) “Global Climate Change and the Origin of
Modern Benthic Communities in Antarctica”
AMER. ZOOL., 41:27–39, Figures 1 and 3b.
U. RADWA¡SKA & A. RADWA¡SKI (2003) “The Jurassic crinoid genus Cyclocrinus D’ORBIGNY, 1850:
still an enigma” Acta
Geologica Polonica, Vol.
53 (2003), No. 4, pp. 301-320 Figures 3, 8, 9, 10, 11, 12, 13, and 14.
http://www.geo.uw.edu.pl/agp/table/pdf/53-4/radwanscy.pdf
R. T. SCHELBLE et al (2001) “HEMATITE
MINERALIZED BACTERIAL REMNANTS: IMPLICATIONS FOR MARTIAN HEMATITE DEPOSITS”
LPSC XXXII 1438.pdf.
“by Fe-oxides for extended
periods of time. Although
banded
iron formations have not so far been recognized
on
Mars, hematite deposits have been observed.
Christensen,
et al. [7] cite five possibilities for the origin
of
the hematite deposits:
· Direct
precipitation from standing, oxygenated
iron-rich
water
· Precipitation
from iron-rich hydrothermal fluid
· Low-temperature
dissolution and precipitation
through
mobile groundwater leaching
· Surface
weatherings and coatings
· Thermal
oxidation of magnetite-rich lavas
If
bacteria did exist on Mars, their preservation by
Fe-oxides
in any of these potential settings is possible.
Thus,
the Martian hematite deposits would be an
excellent
site to look for past life on Mars.
A.
Krasnopolsky et al. “DETECTION
OF METHANE IN THE MARTIAN ATMOSPHERE: EVIDENCE FOR LIFE” V. European
Geosciences Union 1st General Assembly, Nice, France, 25 - 30
April 2004. Available online at: http://www.cosis.net/abstracts/EGU04/06169/EGU04-A-06169.pdf
Using
the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we
observed a spectrum of Mars at the P-branch of the strongest CH4 band at 3.3 µm with
resolving power of 220,000. Summing up the spectral intervals at the expected
positions of 18 strongest Doppler-shifted martian lines, we detected the
absorption by martian methane at a 3.9 sigma level. The observed CH4 mixing ratio
is 11 ± 4
ppb. Total photochemical loss of CH4 in the martian atmosphere is equal to 1.8×105 cm−2 s−1, and the CH4 lifetime is
440 years. Heterogeneous loss of atmospheric methane is probably negligible,
while the sink of CH4 during
its diffusion through the regolith may be significant. There are no processes
of CH4 formation
in the atmosphere, so the photochemical loss must therefore be balanced by
abiogenic and biogenic sources. The mantle outgassing of CH4 is 4000 cm−2 s−1 on the Earth and smaller by an order
of
magnitude on Mars. The calculated production of CH4 by cometary impacts is 2.3 per cent
of the methane loss. Methane cannot originate from an extinct biosphere, as in
the case of “natural gas” on Earth, given the exceedingly low limits on organic
matter set by the Viking landers and the dry recent history which has been
extremely hostile to the macroscopic life needed to generate the gas.
Therefore, methanogenesis by living subterranean organisms is the most likely
explanation for this discovery. Our
estimates
of the biomass and its production using the measured CH4 abundance show that the martian
biota may be extremely scarce and Mars may be generally sterile except for some
oases.
M. J. Mumma et al (2003)“[14.18] A Sensitive Search
for Methane on Mars.” DPS 35th Meeting,
1-6 September 2003 Session 14. Mars Atmosphere II Poster, Highlighted on,
Wednesday, September 3, 2003, 3:00-5:30pm, Sierra Ballroom I-II.
“CH4 and its oxidation products (H2CO,
CH3OH, C2H6) on Mars have received both
observational (1) and theoretical attention (2, 3), but have not been firmly
detected. Owing to its short photochemical lifetime (~ 300 years), the
existence of significant methane would indicate \underline{recent} release from
sub-surface reservoirs; a quantitative measure of the release rate could be
inferred from its present atmospheric abundance. Sub-surface methane could be
primordial (reduced cosmogonic carbon) (1) or biotic in origin (4); local
enhancements are expected if methane is released from discrete regions. The
presence of sub-surface hydrogen concentrations on Mars has been inferred from
local-enhancements in epithermal neutron fluxes measured on Mars Odyssey (5),
however, independent evidence is required to establish its likely chemical form
(e.g., water vs. hydrocarbons) in low-latitude sites (Amazonia Planitia, and
Schiaparelli-Cassini). We suggest that enhanced methane there could test
whether sub-surface hydrogen is chemically bound in hydrocarbon moieties. In
any case, a quantitative measure of methane production would provide a key for
assessing models of biogenic vs. primordial origins. “
