Density of Mars' South Polar Layered Deposits

Details Density of Mars' South Polar Layered Deposits Density of Mars' South Polar Layered Deposits

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p24a..07z&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P24A-07

Computer Science

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5417 Gravitational Fields (1221), 5422 Ices, 6225 Mars

Scientific paper

The Martian south polar layered deposits (SPLD) contain the south polar residual ice cap and smooth, low- albedo surroundings that collectively rise about 3 km above surrounding cratered highlands terrain. The residual polar cap component is believed to be composed of water ice with an unknown admixed dust component that is overlain by a thin (1-10 m) predominantly CO2 cover. The CO2 veneer contains "swiss cheese-like" shallow depressions that reveal the underlying water ice at their bases. The more spatially extensive part of the SPLD has a low albedo and dust-like spectral signature, which raises the question whether the dominant component of the SPLD as a whole is volatile (H2O and/or CO2) or dust. In this study we use initial high-resolution gravity observations from X-band (8.4 GHz) Doppler tracking of the Mars Reconnaissance Orbiter (MRO), together with the volume obtained by combining surface topography from the Mars Orbiter Laser Altimeter (MOLA) and basal topography from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) to calculate the density of the SPLD and constrain its composition. We find the best-fit density by calculating the predicted gravity field from the observed structure of the SPLD and underlying structure. We determine the contributions to the gravity from the topography along the Moho, crustal surface, and SPLD surface, accounting for the finite amplitude of the topography. We iterate the SPLD density to find the best fit between the modeled and observed gravity. Results indicate a best-fit density of 1220 kg m-3, which is consistent with water ice with approximately 15% admixed dust. Our results indicate that despite the dust-like albedo and spectral signature over most of its surface, the SPLD are likely composed of relatively clean water ice. The result refines the Martian surface water inventory. These deposits represent the largest known surface reservoir of water on Mars today, and the largest in the inner solar system outside the Earth.

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