Lack of meltwater may prevent radar sounding measurements of supraglacial debris thickness in the martian midlatitudes

Introduction: Lobate debris aprons (LDA) are among the purest reservoirs of water ice in Mars’ midlatitudes. Furrow and ridge morphology suggests viscous deformation akin to compressional features observed on terrestrial rock/debris-covered glaciers, where ice ablation is prevented due to an insulating debris layer[1-3]. Depth-corrected orbital radar sounding detections of LDA bases consistently constrain their bulk dielectric properties to that of cold, highpurity water ice with thicknesses on the order of hundreds of meters [4-6]. Due to their relatively low latitude, high purity, and large volume, LDA may be among the strongest candidates for targeting martian water and life resources for future exploration. A significant challenge in targeting sites with low risk and high scientific return for mission planning is understanding the distribution of supraglacial debris thickness in relation to ice concentration. To date, no near-subsurface radar returns have been interpreted as reflections from a debris-ice contact; either the dielectric contrast is negligible or the contact is too shallow to distinguish from the side-lobes of the compressed pulse [7]. While the theoretical vertical resolution of SHARD is approximately 10 m for the dielectric permittivity of ice [8] and the lack of an internal reflection could signify relatively thin debris, a graded contact or surface scattering could also contribute to the nondetection of a debris layer upwards of 30 m thick.