Search for subsurface liquid water in MARSIS data

After the first evidence of subglacial liquid water in the subsurface near the Martian South Pole the search for further evidence of liquid water in that area has become a driver in the analysis of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) data. If this discovery is not an isolated case it could be possible to find a liquid water system in the subsurface. In this work data of Martian South Pole collected by MARSIS are analysed. These echoes are used to map the characteristics of Mars ground and underground topography because their power values change with the composition of the soil. The power values of the echoes depend on the altitude of the spacecraft and on distortion due to ionosphere. Ionospheric distortions can’t be completely eliminated, then a precise data calibration is not possible. These problems are addressed with an empirical calibration of surface and subsurface reflected data based on the assumption that different orbits passing above the same point have to collect the same value of surface echo power. After these operations the calibrated maps of the Southern Residual Ice Cap (SRIC) and of the South Polar Layered Deposits (SPLD) show that their surface reflectivity are significantly different, while their subsurface characteristics seem to be similar. The comparison of these two areas confirms the previous studies about the surface composition of the Polar Cap covered by few meters thick layer of CO2 ice responsible for weak reflections. The analysis of the SPLD highlights the presence of bright reflectors near the subglacial lake, already found by recent studies and additional zones with high basal echoes undetected before. These could be the target for future investigation since they are likely to host small liquid water bodies in subsurface.