Water ice concentration and distribution in the Martian south polar layered deposits constrained by the lateral variations of their bulk density

Records of Mars' climate history have been preserved by the ice-rich south polar layered deposits. An accurate knowledge of their properties is key to understanding the evolution of Mars. The combination of geophysical measurements, including gravity, altimetry and radar sounding, enables constraints on the density and composition of the south polar cap. We present a novel method that enables a thorough detection of the gravitational disturbances that are associated with lateral density variations in the ice deposits. A constrained least-squares technique is used to carry out a density inversion based on the modeling of mass concentrations, which represent local mass anomalies within the polar cap. The estimated density of the deposits varies locally in the range 850−1650kg mˆ-3. A composition inversion was then carried out to investigate the volume fractions of dust, water ice, and dry ice. The local percentage of each constituent is accounted for to map out the lateral variations of the deposits composition and dielectric constant. Our results show a higher level of dust (15-30 vol%) on the west side of the deposits edge that is the boundary of the Dorsa Argentea Formation. We note that at least 80.5% of the area covered by the south polar deposits is characterized by a high concentration of water ice (≥50%), including areas where high basal echo power signatures were detected by the Mars Advanced Radar for Subsurface and Ionospheric Sounding. The volume of H2O ice in the south polar deposits is constrained to be between 1.0×106−1.3×106km3 (60−80% of the total).