Planetary Science Seminar spring-2016

Ceres in the light of Dawn: One year of geological observations and the case for near-surface ground ice

On 6 March 2015 NASA’s Dawn mission became the first spacecraft to visit the dwarf planet Ceres, the largest asteroid, and the only large asteroid having a density so low (2.161 g/cm3) that it requires the presence of appreciable water. We report spectroscopic (both reflectance and neutron) and geomorphological evidence for near-surface ground ice on Ceres in the form of ubiquitous flow features, pits, reduced neutron counts, and the direct detection of water. The observed flow features exist on a morphological continuum between two endmembers: (1) thick, domical flows with well-developed snouts, and (2) thin, sheeted, multi-lobed flows with very long runouts. We interpret these features to be similar to ice-cored or ice-cemented flows, and ballistically emplaced fluidized ejecta respectively. A large population of morphologically intermediate flows also exists; they have been interpreted as being a mix of long-runout landslides and fluidized ejecta emplaced as surface flows.