Planum Australe

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Planum Australe, taken by Mars Global Surveyor.

Planum Australe (Latin: "the southern plain") is the southern polar plain on Mars. It extends southward of roughly 75°S. 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.

1 Ice cap
- 1.1 Martian spiders
2 Features
3 References
4 See also
5 External links

[edit] Ice cap

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 metre thick.^[1] It is possible that the area of this ice cap may be shrinking due to localised climate change or more widespread global warming.^[2]

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 poles 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.^[3].

Data from ESA's Mars 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 by permafrost fields that extend for tens of kilometres north away from the scarps.^[4]

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 massive impact basins in the western hemisphere - Hellas Planitia and Argyre Planitia - creates an immobile area of low pressure over the permanent ice cap. The resulting weather patterns produce fluffy white snow which has a high albedo. This is in contrast to the blacker snow that forms in the eastern part of the polar region, which receives little snow.^[5]

[edit] Martian spiders

Main article: Martian spiders

A unique phenomenon associated with the southern ice cap of Mars is the appearance of geological formations which look like spider webs as the carbon dioxide ice thaws in the Martian spring. These are referred to as Martian spiders. The formation of these structures is not fully understood, with many theories being put forward by astrogeologists.

[edit] Features

Elevation map of the south pole. Note how Planum Australe rises above the surrounding cratered terrain. Click to enlarge and for more info.

There are two distinct subregions in Planum Australe - Australe Lingula and Promethei Lingula. It is dissected by canyons Promethei Chasma, Ultimum Chasma, Chasma Australe and Australe Sulci. It is theorised that these canyons were created by katabatic wind.^[6] The largest crater in Planum Australe is McMurdo Crater.

[edit] References

^ Phillips, Tony. Mars is Melting. Science @ NASA. Retrieved on October 20, 2006.
^ Sigurdsson, Steinn. Global warming on Mars?. RealClimate.org. Retrieved on October 20, 2006.
^ Byrne, Shane (14 February). "A Sublimation Model for Martian South Polar Ice Features". Science 299: 1051 - 1053.
^ Water at Martian south pole. European Space Agency. Retrieved on October 22, 2006.
^ Mars' South Pole mystery. Spaceflight Now. Retrieved on October 26, 2006.
^ Kolb, Eric J.; Kenneth L. Tanaka (2006). "Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars". The Mars Journal 2: 1-9. DOI:10.1555/mars.2006.0001.