Marked by large depressions in the mantle, this observation shows an area south of the Hellas region in the southern hemisphere of Mars.

The large depressions have scalloped edges and appear to have formed from multiple smaller depressions, also with scalloped edges, that have coalesced together. Scalloped pits such as these are typical features of the mid-latitude mantle and are most commonly found at approximately 55 degrees north and south latitude. The presence of scalloped pits has led to hypotheses of the removal of subsurface material, possibly interstitial ice, by sublimation (the process of solid material going directly to a gaseous state).

Scalloped pits, such as these, typically have a steep pole-facing scarp and a gentler equator-facing slope. This is most likely due to differences in solar heating.

The formation of some scalloped depressions is believed to be an ongoing process today.

On the surface surrounding the scalloped depressions are multiple criss-crossing dark streaks; these are formed by dust devils. Dust devils are spinning, columnar vortices of wind that commonly occur in dry and desert landscapes on Earth as well as Mars. They move across the landscape leaving a dark streak by removing bright dust from the terrain in their path and revealing a darker surface underneath. Some of the dark streaks in this image cross the depressions indicating that dust devils have been active since the formation of the depressions.
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.