Vesta’s Geological Features

Abstract

The Dawn spacecraft collected over 28,000 images and a wealth of spectral data of Vesta’s surface. These data enable analysis of Vesta’s diverse geology including impact craters of all sizes and unusual shapes, a variety of ejecta blankets, large troughs, impact basins, enigmatic dark material, and considerable evidence for mass wasting and surface alteration processes. Two large impact basins, Veneneia underlying the larger Rheasilvia basin dominate the south polar region. The depression surrounding Vesta’s south pole was formed by two giant impacts about one billion and two billion years ago. Vesta’s global tectonic patterns (two distinct sets of large troughs orthogonal to the axes of the impacts) strongly correlate with the locations of the two south polar impact basins, and were likely created by their formation. Numerous unusual asymmetric impact craters and ejecta indicate the strong influence of topographic slope in cratering on Vesta. One type of gully in crater walls is interpreted to form by dry granular flow, but another type is consistent with transient water flow. Very steep topographic slopes near to the angle of repose are common; slope failures make resurfacing due to impacts and their associated gravitational slumping and seismic effects an important geologic process on Vesta. Clusters of pits in combination with impact melt suggest the presence of volatile materials underlying that melt in some crater floors. Relatively dark material of uncertain origin is intermixed in the regolith layers and partially excavated by younger impacts yielding dark outcrops, rays and ejecta. Vesta’s surface is reworked by intense impacts and thus much younger than the formation of its crust.