Comment on ‘High Frequency Radar Perspective of Putative Subglacial Liquid Water on Mars’ by Morgan et al. (2025)

The presence of liquid water beneath the Martian South Polar Layered Deposits (SPLD) was inferred from strong subsurface reflections detected by the MARSIS radar (Orosei et al., 2018). Morgan et al. (2025) recently reported much weaker basal echoes recorded by the SHARAD radar over the same area, and used simulations and signal inversion to interpret them. We repeated their computations finding large, irreconcilable discrepancies. We conclude that interpretation of SHARAD data will require an accurate determination of the loss tangent in the SPLD in order to reliably estimate the electromagnetic properties of the basal unit. Plain Language Summary A recent study by Morgan et al. (2025) used specialized radar data to analyze the base of the Martian south pole. Their results contradicted previous findings of potential liquid water, suggesting a much drier material instead. However, when we attempted to replicate their method, we could not get their results. We identified errors in their model about how radar signals propagate through ice and we concluded that their method is not able to identify what lies beneath the Martian surface. Future research must more accurately account for signal loss before drawing conclusions about the nature of the material beneath the Martian South polar deposits.