Replenishment Of Near-Surface Water Ice By Impacts Into Ceres' Volatile-Rich Crust: Observations By Dawn'S Gamma Ray And Neutron Detector

Ceres' regolith contains water ice that has receded in response to insolation-driven sublimation. Specially targeted, high spatial-resolution measurements of hydrogen by Dawn's Gamma Ray and Neutron Detector (GRaND) reveal elevated hydrogen concentrations in and around Occator, a young, 90 km diameter, complex crater located at 19.82 degrees N where near-surface ice is not expected. The excess hydrogen can be explained by impact excavation of water-rich outer crustal materials and their emplacement in the crater floor and ejecta blanket. This is supported by thermophysical models that show water ice could survive at sub-meter depths, given Occator's relatively young age (similar to 20 Myr). We hypothesize that the regolith can be replenished with ice from large impacts and that this process partially controls the distribution and depth of near surface ice. This is supported by results from Occator and similarities in the global distribution of hydrogen and the pattern of large craters (20-100 km diameter).