Surface and subsurface study of unusual ice scarps, southern polar cap of Mars
Résumé
The southern polar cap of Mars, known as Planum Australe, is a 1.6 x 106 km3 ice sheet made of water ice with a 0 to 15 % dust rate. It is structured of isochrone layers deposited over several hundreds of millions of years, and reaching 3700 m of maximum thickness. Those features make the cap comparable to the continental ice sheets on Earth. However, low surface temperatures (155 K), weak atmospheric pressure (0.008 bars) and other typical Martian parameters could make the ice to have mechanical and dynamic behaviors, at any scales, somewhat different to those known under terrestrial conditions. Such behaviors remain to be detected. Unusual ice scarps are observed over a well defined region of Planum Australe. They have a 500 m average height and a typical length of about 30 km. Their particular size and shape are unknown neither on the northern Martian cap nor on the Earth. So far few studies, based on analysis of low resolution images, suggested a wind formation process. The sounding radar SHARAD onboard the NASA's Mars Reconnaissance Orbiter spacecraft, is able to penetrate as far as 1000 m deep into water ice materials with a vertical x alongtrack resolution of 7 m x 300 m respectively. This dataset is an opportunity to study the subsurface structure of those unusual scarps. We will present a work aiming to draw up a complete description of those objects on and below the surface. The obtained profile could be better explained by a more brutal event than a wind-formed mechanism. Different suggestions for this formation process will be exposed. We will emphasize that to be fully explained, the formation process needs an effort to better understand the rheology of Martian ices. Those results will be presented in a regional context.