Image PSP_004077_1325 shows the edge of a dark dune field on the floor of Proctor Crater, a 150 kilometer diameter crater in the southern highlands of Mars.

The dark dunes are composed of basaltic sand that has collected on the bottom of the crater. Dark dune slip faces (the steeper sides of the dunes) are located on the east side of the dunes and are believed to have formed in response to fall and winter westerly winds caused by geostrophic forces (winds balanced by Coriolis and pressure gradient forces). Superimposed on their surface are smaller secondary dunes that are commonly seen on terrestrial dunes of this size.

Many smaller and brighter bed forms, most likely small dunes or granule ripples, cover the substrate between the larger dark dunes as well as most of the floor of Proctor Crater. The dark dunes overlie the small bright bedforms indicating that they formed more recently. In several areas, however, the dark dunes appear to influence the orientation of the small bright dunes, possibly by wind flowing around the larger ones, suggesting that both dark and bright bedforms are coeval. The dunes in Proctor Crater may be active today, moving in response to Martian winds.
Written by: Maria Banks

All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible: Image: NASA/JPL/University of Arizona

For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.