Global variations in regolith properties on asteroid Vesta from Dawn's low-altitude mapping orbit

We investigate the depth, variability, and history of regolith on asteroid Vesta using data from the Dawn spacecraft. High-resolution (15-20 m pixel(-1)) Framing Camera images are used to assess the presence of morphologic indicators of a shallow regolith, including the presence of blocks in crater ejecta, spur-and-gully-type features in crater walls, and the retention of small (<300 m) impact craters. Such features reveal that the broad, regional heterogeneities observed on Vesta in terms of albedo and surface composition extend to the physical properties of the upper similar to 1 km of the surface. Regions of thin regolith are found within the Rheasilvia basin and at equatorial latitudes from similar to 0-90 degrees E and similar to 260-360 degrees E. Craters in these areas that appear to excavate material from beneath the regolith have more diogenitic (Rheasilvia, 0-90 degrees E) and cumulate eucrite (260-360 degrees E) compositions. A region of especially thick regolith, where depths generally exceed 1 km, is found from similar to 100-240 degrees E and corresponds to heavily cratered, low-albedo surface with a basaltic eucrite composition enriched in carbonaceous chondrite material. The presence of a thick regolith in this area supports the idea that this is an ancient terrain that has accumulated a larger component of exogenic debris. We find evidence for the gardening of crater ejecta toward more howarditic compositions, consistent with regolith mixing being the dominant form of weathering on Vesta.