Site of south polarsubglacial water body (reported July 2018)Elevation map of the south pole. Note how Planum Australe rises above the surrounding cratered terrain. Click to enlarge and for more info.
Planum Australe is partially covered by a permanentpolar ice cap composed of frozenwater andcarbon dioxide about 3 km thick. A seasonal ice cap forms on top of the permanent one during the Martian winter, extending from 60°S southwards. It is, at the height of winter, approximately 1 meter thick.[5] It is possible that the area of this ice cap may be shrinking due to localizedclimate change.[6] Claims of more planetwideglobal warming based on imagery, however, ignore temperature data and global datasets. Spacecraft and microwave data indicate global average temperature is, at most, stable,[7][8] and possibly cooling.[9][10][11]
In 1966, Leighton and Murray proposed that the Martian polar caps provided a store of CO2 much larger than the atmospheric reservoir. However it is now thought that both polar caps are made mostly of water ice. Both poles have a thin seasonal covering of CO2, while in addition the southern pole has a permanent residual CO2 cap, about 8 to 10 metres thick, that lies on top of the water ice. Perhaps the key argument that the bulk of the ice is water is that CO2 ice isn't mechanically strong enough to make a 3 km thick ice cap stable over long periods of time.[12] Recent evidence fromSHARAD ice penetrating radar has revealed a massive subsurface CO2 ice deposit approximately equal to 80% of the current atmosphere, or 4–5 mbar, stored in Planum Australe.[13]
Depiction of erupting south polar sand-laden jets (Ron Miller)
Data fromESA'sMars Express indicates that there are three main parts to the ice cap. The most reflective part of the ice cap is approximately 85%dry ice and 15% water ice. The second part, where the ice cap forms steep slopes at the boundary with the surrounding plain, is almost exclusively water ice. Finally, the ice cap is surrounded bypermafrost fields that extend for tens of kilometres north away from the scarps.[14]
The centre of the permanent ice cap is not located at 90°S but rather approximately 150 kilometres north of the geographical south pole. The presence of two massiveimpact basins in the western hemisphere –Hellas Planitia andArgyre Planitia – creates an immobilearea of low pressure over the permanent ice cap. The resulting weather patterns produce fluffy whitesnow which has a highalbedo. This is in contrast to theblack ice that forms in the eastern part of the polar region, which receives little snow.[15]
The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight.[17] Then, sublimed CO2 (and probably water) increase pressure in their interior, producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.[18][19][20][21] This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars. TheMars Geyser Hopper lander is a concept mission that would investigate the geysers of Mars.[22][23]
In September 2020, scientists confirmed the existence of several largesaltwater lakes under theice in the south polar region of the planetMars. According to one of the researchers, “We identified the same body of water [as suggested earlier in a preliminary initial detection], but we also found three other bodies of water around the main one ... It’s a complex system.”[24][25]
^Mangold, N (2011). "Ice sublimation as a geomorphic process: A planetary perspective".Geomorphology.126 (1–2):1–17.doi:10.1016/j.geomorph.2010.11.009.
^Landis, Geoffrey A.; Oleson, Steven J.; McGuire, Melissa (9 January 2012).Design Study for a Mars Geyser Hopper(PDF). 50th AIAA Aerospace Sciences Conference. Glenn Research Center, NASA. AIAA-2012-0631. Retrieved2012-07-01.
