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The origin of perennial water-ice at the South Pole of Mars

13 July 2007

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The OMEGA instrument on board ESA’s Mars Express has characterised the types of ice deposits present in the South polar cap of Mars as the arrows, superimposed on an image taken by the HRSC instrument, indicate.

Credits: ESA - DLR - FU Berlin (G. Neukum)

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The OMEGA instrument on board ESA’s Mars Express has shown that the perennial deposits on the Martian South Pole are of essentially three types (referred to as ‘units’ in this image): water-ice mixed with carbon dioxide (CO2) ice, tens-of-kilometres-wide patches of water-ice, and deposits covered by a thin layer of CO2 ice.

Credits: Left: USGS; Right: OMEGA team - F.Montmessin - Service d'Aéronomie du CNRS - IPSL

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These images, generated thanks to Martian Global Climate Models (GCMs), provide a comparison between the water-ice accumulation rates in two different periods (present day and 21 500 years ago), corresponding to inversed planetary precession periods.

Present-day map shows a net accumulation of water-ice only at the South Pole itself, where the existence of a CO2 cold-trap forces a local and permanent deposition of water-ice. In the inversed situation (21 500 years ago), the CO2 cold trap has been removed and the pattern of accumulation is only controlled by the precipitation/sublimation of water vapour on an annual average.

Credits: OMEGA team - F.Montmessin - Service d'Aéronomie du CNRS - IPSL

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A scenario for the recent evolution of water ice at the South Pole of Mars, summarizing the sequence of events in the south polar region since the precession cycle of Mars was last inverted. At that time (1), water was extracted off the north polar cap and was deposited over the south layered terrains. The passage to present-day configuration (2), with inverted precession cycle, forced water to progressively return back to the North Pole. In a third act (3), the water-ice erosion process stopped as permanent CO2 ice slabs formed and kept water from subliming further.

Credits: OMEGA team - F.Montmessin - Service d'Aéronomie du CNRS - IPSL

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