HR: 1340h
AN: P33A-1017    [Abstracts]
TI: Constraints on the composition of the Martian south polar cap from gravity and topography
AU: * Wieczorek, M A
EM: wieczor@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 avenue de Neptune, Saint Maur, 94107, France
AB: The polar caps of Mars have long been acknowledged to be composed of unknown proportions of water ice, solid CO₂ (dry ice), and dust. Gravity and topography data are here analyzed over the southern cap to place constraints on its density, and hence composition. Using a localized spectral analysis and the assumption that the polar cap is uncompensated (as attested by data obtained from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) experiment), the density of the volatile-rich south polar layered deposits is constrained to be 1175±55~kg~m^-3. A maximum of about 40% dry ice by volume could be sequestered in these deposits if they were completely dust free. Alternatively, if these deposits were completely free of solid CO₂, the dust content would be constrained to lie between about 10 and 20% by volume. The bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust. However, even if a moderate quantity of solid CO₂ were present as horizontal layers, the bulk thermal conductivity of the polar cap would be significantly reduced. Reasonable estimates of the present day heat flow of Mars predict that dry ice beneath the thicker portions of the south polar cap would have melted. Depending on the quantity of solid CO₂ in these deposits today, it is even possible that water ice could melt where the cap is thickest. If independent estimates for either the dust or CO₂ content of the south polar cap could be obtained, and if MARSIS data could determine whether this polar cap is presently experiencing basal melting or not, it would be possible to use these observations to place tight constraints on the present day heat flow of Mars.
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 5416 Glaciation
DE: 5417 Gravitational fields (1221)
DE: 5462 Polar regions
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting