An endogenic origin of cerean organics

Abstract

Localized deposits of aliphatic organic-rich material have been found on the surface of dwarf planet Ceres, and based on mineralogical context, it has been suggested that these organics formed within Ceres (De Sanctis et al., 2017). However, no obvious source and exposure mechanism can be inferred from the geological settings of the organic-rich terrains. The alternative hypothesis is that the organics were delivered from an exogenic source via impact (Pieters et al., 2018). We numerically simulate the thermal degradation of aliphatic organics delivered to Ceres during hypervelocity impacts, as well as the thermal degradation and excavation of organics from the subsurface. Our models show that exogenic delivery of aliphatic organics is inefficient, as most of the spectral signature of the organic species would be thermally degraded and diluted by mixing with target material in the ejecta blanket of a given crater. Instead, our models suggest that the formation of Ernutet crater excavated a subsurface reservoir of aliphatic organics from a depth of 3-6 km, bringing it close to the surface, where it could be subsequently exhumed by small craters and landslides, compatible with observations.