High Frequency Radar Perspective of Putative Subglacial Liquid Water on Mars

Abstract Anomalously bright radar reflections from the base of Mars' south polar cap raise the tantalizing possibility of present‐day liquid water. Orosei et al. (2018, https://doi.org/10.1126/science.aar7268 ) first reported bright subsurface echoes from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) prompting studies of whether the high reflectivity, stems from liquid water or dry scattering interfaces. A key challenge has been the prior inability of the higher‐frequency Shallow Radar (SHARAD) to detect this basal zone, hindering potential diagnostic cross‐frequency comparisons. Due to a novel spacecraft maneuver, SHARAD has now obtained a basal return associated with the putative body of water. Modeling of the radar response is not consistent with the liquid water explanation, instead suggesting a localized, low roughness region of dry rock/dust beneath the ice could explain the SHARAD response. Reconciling the divergent responses of SHARAD and MARSIS remains essential to determine the nature of this anomalous south polar region.