Influence of Volatiles on Mass Wasting Processes on Vesta and Ceres

Kurzfassung

We have analyzed mass wasting features, their distribution and deposit geometry on the two largest main asteroid belt objects - protoplanet Vesta and dwarf planet Ceres - and compared their geomorphology and mobility. Both asteroids have similar surface accelerations, but different surface compositions. Based on our observations and previous studies, we categorized three distinct morphological mass wasting classes: slumps, slides, and flow-like movements. We conclude that Ceres has abundant features of flow-like mass movements. Further, sliding and flow-like characteristics are identified in craters within mid-latitudes which supports the possibility of the presence of water ice in the near subsurface of Ceres. Vesta predominantly shows characteristics of dry granular-like slide features which are distributed homogenously across the surface. By plotting the ratio between fall height (H) and run-out length (L) (effective coefficient of friction, H/L) against the run-out length and spreading width (W), we demonstrate that deposits on Vesta terminate on shorter distances, whereas on Ceres they travel longer distances. The deposit geometry and the similar surface gravity on both asteroids suggest that the material composition and volatile component have a significant effect on deposit emplacement. However, both bodies' mass movements have similar effective coefficients of friction, even though Vesta's regolith is comparatively dry, whereas Ceres is rich in water ice. This leads to the conclusion that volatile content alone cannot be responsible for low effective coefficients of friction, and that more than one geological process is needed to explain the mass motion behavior and morphology.