Planum Australe

Planum Australe

Planum Australe, taken by Mars Global Surveyor.
Coordinates	83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0Coordinates: 83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0

Planum Australe (Latin: "the southern plain") is the southern polar plain on Mars. It extends southward of roughly 75°S and is centered at 83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0. The geology of this region was to be explored by the failed NASA mission Mars Polar Lander, which lost contact on entry into the Martian atmosphere.

Planum Australe is partially covered by a permanent polar ice cap composed of frozen water and carbon 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. It is possible that the area of this ice cap may be shrinking due to localized climate change. Claims of more planetwide global warming based on imagery, however, ignore temperature data and global datasets. Spacecraft and microwave data indicate global average temperature is, at most, stable, and possibly cooling.

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. Recent evidence from SHARAD 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.