This image from NASA's Dawn spacecraft shows a close-up view of the wall of the Rheasilvia impact basin on Vesta. Rheasilvia, which is 310 miles or 500 kilometers in diameter, dominates southern Vesta.
This image was obtained by the Dawn framing camera on Dec. 27, 2011, during the spacecraft's low-altitude mapping orbit (on average 130 miles or 210 kilometers above the surface). Framing camera images from this orbit provide the first look at the detailed geology of the basin, where rock or fractured rock is exposed within the basin wall. The scene covers approximately 170 square miles (430 square kilometers).
More information about the Dawn mission is online at http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov.