A handout photo released by Nasa shows a digital terrain model generated from a stereo pair of images taken by the High Resolution Imaging Science Experiment (HiRISE) camera on Nasa's Mars Reconnaissance Orbiter, providing this synthesised, oblique view of a portion of the wall terraces of Mojave Crater in the Xanthe Terra region of Mars. This view, in which the vertical dimension is exaggerated three-fold compared with horizontal dimensions, shows the ponding of material backed up behind massive wall-terrace blocks of bedrock. Hundreds of impact craters on Mars have similarly ponded features with pitted surfaces. These "pitted ponds" are thought to result when material melted by the crater-causing impacts is captured behind the wall terraces.