Bright and Dark Dunes
This image shows a large sand dune with bright patches. Martian dunes near the poles often have bright patches in the spring, when seasonal frost is lingering. However, this image is from late summer, when frost is long gone. What is going on here?
A close-up look with HiRISE provides some clues. The bright patches are made up of large ridges that look like wind-blown bedforms. Additionally, the bright patches are yellowish in the infrared-red-blue image. In enhanced color, most sand on Mars is blue but dust is yellow. This suggests that the bright bedforms are either built from, or covered by, dust or material with a different composition.
The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. (The original image scale is 49.9 centimeters [19.6 inches] per pixel [with 2 x 2 binning]; objects on the order of 150 centimeters [59.1 inches] across are resolved.) North is up.
The University of Arizona, in Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.