Fluidized Appearing Ejecta on Ceres: Implications for the Mechanical Properties, Frictional Properties, and Composition of its Shallow Subsurface

Abstract

AbstractSeveral ejecta deposits on Ceres display morphological characteristics not commonly associated with dry ballistic emplacement. We characterized 30 examples of fluidized appearing ejecta (FAE) on Ceres and identified two distinct morphological populations: cuspate/lobate FAE and channelized FAE. The cuspate/lobate FAE typically display one or more of the following characteristics: well‐defined margins, a sheeted or layered appearance, arcuate or cuspate terminal lobes, and occasional mass concentrations at their distal margins. The channelized FAE typically display a morphology dominated by topographically focused channelized flows and arcuate terminal lobes but lack the well‐defined margins common among their cuspate/lobate counterparts. Although Cerean FAE are holistically distinct from rampart/layered ejecta craters on Mars, Ganymede, and other icy solar system objects, many of their aforementioned morphological characteristics are commonly found among these other examples of fluidized ejecta. The formation of Martian and icy satellite fluidized ejecta has been widely attributed to the mobilization of near‐surface volatiles, namely, water ice. The documented Cerean FAE are observed between absolute latitudes of 70°, with a slight enrichment in the midlatitudes of the southern hemisphere. We test the hypothesis that the morphologies and mobilities of Cerean FAE can be explained via impacting into a low‐cohesion ice‐silicate target material, followed by material sliding on a low‐friction partially icy substrate. We do this by comparing the observed Cerean FAE to a kinematic‐dynamic sliding ejecta emplacement model. We find that a mechanically weak, H2O‐rich near‐surface layer is consistent with the range of ejecta mobilities and morphologies observed in this investigation.