This observation shows partial views of two high latitude pits. These polar pits contain gullies, small-scale slope features that are proposed to require some amount of liquid water to form.

Several of the gullies have multiple channels and debris aprons from numerous flows that occurred throughout time. Many of the gullies are seen to originate at a boulder layer at the pit edges. This layer is deteriorating and releasing boulders that can be seen rolling down the pit walls. The bright material near the pit edges is probably seasonal frost.

What is particularly interesting about these gullies is that some might be forming (see subimage, approximately 800 meters across, of the south-facing gullies in the bottom pit; 1590 x 1445; 7 MB). The gullies on this wall have incised alcoves, but only a few have well-developed channels.

This could be a region of current gully formation. Aiding this hypothesis is the fact that there are a couple of depressions between the visible gullies, suggestive of a developing gully where water and/or material removed from under the surface caused the overlying ground to collapse. It is also possible that water originating on the surface is carving out these depressions, although it is difficult to melt water ice at the temperatures found in this particular location.
Written by: Kelly Kolb

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.