This image, near the southeast rim of Peneus Patera crater, is marked by depressions in the mantle with scalloped edges. Several of the depressions have apparently coalesced together.

These features are most commonly found at approximately 55 degrees north and south latitude. Their presence has led to hypotheses of the removal of subsurface material, possibly interstitial ice by sublimation (evaporation).

Steep scarps consistently face the south pole while more gentle slopes face in the direction of the equator. This is most likely due to differences in solar heating.

A polygonal pattern of fractures, commonly associated with "scalloped terrain," can be found on the surface surrounding and within the depressions. The fractures indicate that the surface has undergone stress that may have been caused by subsidence, desiccation, or thermal contraction.

Scallop formation is believed to be an ongoing process at the present time.
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.