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_0930
http://www.franontanaya.com/blog/wp-...defrosting.jpg

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.

Pingo
http://en.wikipedia.org/wiki/Pingo

A Pingo in the Northwest Territories, Canada.
http://www.geo.uu.nl/fg/berendsen/pi...aska/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...arvin_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

Attached Images

	marsdefrostinga.jpg (92.1 KB, 1 views)
	Pingoa.jpg (130.5 KB, 1 views)
	garvin_ice2.jpg (57.1 KB, 0 views)
	PIA08583-comp.JPG (9.7 KB, 3 views)

Is there a difference between a Pseudocrater and a Maar. Are they just different names for similar craters?

They both involve lava/liquid water interaction. The pseudocrater is more cone shaped, giving the appearance of a volcano.
The maar is flatter, giving the appearance of an impact crater.
I don't know what are the physical characteristics that would result in a pseudocrater forming rather than a maar.


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