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Posted by Robert Clark on September 19, 2007, 2:00 pm
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> A recently released HIRISE image shows a peak quite close to the Mars
> south pole at 86.7 S latitude. It's appearance is that of a recent
> feature:
>
> Circular Feature Which Looks Like Subsidence and Collapse
>
(PSP_003728_0930).http://hirise.lpl.arizona.edu/PSP_003728_0930http://www.franontanaya.com/blog/wp-content/uploads/2007/09/marsdefro...
>
> A similar polar cone was seen by Mars Global Surveyor but at the north
> pole:
>
> Polar Cone
> MGS MOC Release No. MOC2-1519, 10 July
2006.http://www.msss.com/mars_images/moc/2006/07/10/
>
> Two possibilities for the cone(s) origin. It could be a volcanic
> rootless cone (pseudocrater) or it could be a pingo.
> A pingo is a periglacial feature requiring liquid water in its melt
> phase for its formation. A rootless cone is a volcanic feature
> requiring lava/liquid water interaction for its formation.
> Both of these would require geologically recent liquid water near the
> south pole on Mars.
>
> Pingohttp://en.wikipedia.org/wiki/Pingo
>
> A Pingo in the Northwest Territories,
Canada.http://www.geo.uu.nl/fg/berendsen/pictures/photography/alaska/Pingo.jpg
>
> Pseudocrater. (i.e. rootless cone)http://en.wikipedia.org/wiki/Pseudocrater
>
> Rootless Volcanic Cones South of the Myrdalsjokull Ice Cap
Glacier.http://denali.gsfc.nasa.gov/research/garvin/garvin_ice2.jpg
>
> Possible pingos or pseudocraters have been seen before on Mars though
> at lower latitudes:
>
> Stratigraphical and morphological evidence for pingo genesis in the
> Cerberus plains.http://arrowsmith362.asu.edu/Student_Papers/pingos.pdf
>
> Bob Clark
Both the pseudocrater and pingo explanations would require liquid
water at this extreme southern polar location, which presents a
puzzle.
This animation shows the temperature might reach at best -40 C during
late Spring at 87S latitude:
http://www.mars-ice.org/_more/images/spole_2pm_1.gif
Perhaps during Summer it could get a little warmer, maybe to -30C.
Still a puzzle how you would get liquid water.
It could be volcanic. But the appearance of the feature suggests that
it mirrors the seasonal melting of the CO2 cover in the area, which
implies solar heating in its formation.
One possibility is that it could be due to CO2-water clathrates which
are expected to form on Mars:
PTX PHASE EQUILIBRIA IN THE H2O-CO2-SALT SYSTEM AT MARS NEAR-SURFACE
CONDITIONS.
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1689.pdf
The report states the transition to liquid water brines would occur at
262K if they contain NaCl salt, but this could be down to 230K if they
contain
calcium chloride salts.
Bob Clark
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