Image PSP_004274_1225 is located on the northwestern flank of the volcano Peneus Patera, southwest of Hellas Basin.

The terrain consists of a rough, pitted lower surface and a relatively, smooth upper surface. The lower surface forms oval- to scalloped-shaped edge depressions, several of which have coalesced together. Typically these depressions have a steep pole-facing scarp and a gentler equator-facing slope. The pitted texture of this lower terrain may have formed by the removal of subsurface ice by sublimation, as at this latitude on Mars, the pressure and temperature conditions allow interstitial ground ice to sublime, possibly leading to the formation of depressions.

For example, the roughly circular feature at the top of the image was probably an ancient crater that was filled with the smooth material, possibly composed of ash and dust mixed with interstitial ice. Sublimation of this material subsequently occurred following the crater rim, leaving this circular pattern.
Written by: Alexandra Lefort

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.