Replenishment of near-surface water ice by impacts into Ceres’
volatile-rich crust: Observations by Dawn’s Gamma Ray and Neutron
Detector
Abstract
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 reveal elevated hydrogen concentrations in and around
Occator, a young, 90-km diameter, complex crater located at 19.82N where
near-surface ice is not expected. The excess hydrogen is 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 (~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).