Surface Processes on Vesta – Impact Cratering and Impact Related Mass Movements

Kurzfassung

This work covers the dominant resurfacing processes on asteroid Vesta. The main focus is the analysis of exogenous processes on slopes, such as meteorite impacts and mass movements. The basic input for the analysis are high-resolution images and topographic maps obtained from scientific data of the DAWN spacecraft. A detailed geologic-morphologic mapping of two quadrangles shows that Vesta´s surface is affected by impact craters and different types of mass movement features, such as intra-crater mass wasting, rotational slumping blocks, landslides and gullies. Over-steepened crater rims, formed by the impact itself, cause slope instabilities and promote gravity-forced material to move down the crater wall. Due to the low gravity, impact-induced seismic shaking is the most likely trigger for mass movements on Vesta. In addition, the topography causes many craters to be formed on slopes. These impact craters have an asymmetric shape with a sharp rim on the uphill side and a smooth rim on the downhill side. Geologic and geomorphologic mapping, numerical simulations as well as age determinations show that in most cases, the slope prevents the deposition of ejected material above the uphill rim. In combination with the mass wasting material of the initial slope, a smooth downhill rim is the result of this formation process. Thus, asymmetric craters are the result of a specific form of mass wasting. This thesis shows that mass wasting is the key process for the formation of the morphology on Vesta.