Implications of MOLA topography on the presence of liquid water under the south polar cap of Mars

The existence of liquid water at the base of the south polar layered deposits (SPLD) on Mars has been proposed on the basis of radar data, but dry interpretations have been advanced as well. Here, we consider topography of the SPLD surface above the location of hypothesized water using individual altimetry tracks rather than gridded or interpolated data. Liquid water could create negative surface relief through drainage events and subsequent collapse, or positive surface relief through ice expansion. We find meters of positive topographic relief relative to the surrounding region, consistent with thermal expansion of the ice column from the added geothermal heat that would be required to maintain liquid water at the SPLD base. However, topographic analysis of randomly chosen areas throughout the SPLD suggest that positive topographic relief of this amplitude has a 20% chance of occurring through other processes or statistical noise. Therefore, we conclude that both wet and dry interpretations of the radar data remain viable.