Barchan dunes are common on both Earth and Mars. These dunes are very distinctive in shape, and are important because they can tell scientists about the environment in which they formed.

Barchans form in wind regimes that blow in one dominant direction. The ridged arcs of sand that define the barchan dunes end in horns that point downwind. Sand is transported up the broad, relatively shallow windward slopes and once it overtops the dune crest, the sand falls down a shorter steeper slope between the horns, known as the slip face. Over time, the barchans migrate downwind, following their horns. (The subimage refers to the non-map projected version of the image.)

This HiRISE image shows an example of several barchans merging to form an even larger barchan dune. This can happen through a variety of circumstances, such as when smaller, faster dunes collide with larger, slower-moving dunes that absorb them, resulting in single, larger dunes. The distance between the merging horns of the large dune in this highlighted region is a little over 500 meters (about 1600 feet).

Written by: Andrea Philippoff

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.