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Radar‐sounding surveys associated with the discovery of a large impact crater beneath Hiawatha Glacier, Greenland, revealed bright, flat subglacial reflections hypothesized to originate from a subglacial groundwater table. We test this hypothesis using radiometric and hydrologic analysis of those radar data. The dielectric loss between the reflection from the top of the basal layer and subglacial reflection and their reflectivity difference represent dual constraints upon the complex permittivity of the basal material. Either ice‐cemented debris or fractured, well‐drained bedrock explain the basal layer's radiometric properties. The subglacial reflector's geometry is parallel to isopotential hydraulic head contours, located 7.5–15.3 m below the interface, and 11 ± 7 dB brighter than the ice–basal layer reflection. We conclude that this subglacial reflection is a groundwater table and that its detection was enabled by the wide bandwidth of the radar system and unusual geologic setting, suggesting a path for future direct radar detection of subglacial groundwater elsewhere., Key Points Radiometric and hydrologic analysis of radar‐sounding data is consistent with a reflection from a subglacial groundwater tableDual radiometric constraints indicate a layer of either debris‐laden ice or fractured bedrock above the subglacial groundwater tableThis first detection of a subglacial groundwater table was enabled by favorable local geology, thin ice and the wide bandwidth radar system

Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice‐rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization., Key Points Fresh complex craters on Ceres host distinctive pitted terrains that are morphologically similar to pitted materials on Mars and VestaPitted terrains on Ceres likely form via the rapid volatilization of molecular H2O entrained in impact materialsPitted terrains may be common morphological markers of volatile‐rich near‐surface material in the asteroid belt