This observation shows northern hemisphere gullies on a layered crater wall.

Many channels are visible emanating from beneath layers suggesting that the layers are permeable and carried water to the slope face via the subsurface. It is also possible that the source of water came from the surface. The gullies that do not originate at a layer likely did at one time and have subsequently experienced headward erosion, eroding the layers upslope of their original location.

A mantled unit (smooth terrain) is visible the sources of and within many of the gullies in this image. The mantled unit has been proposed to be remnant snowpack that melts at its bottom to carve gullies. The mantled unit is less abundant in locations where the gullies are most deeply incised, which supports the melting snowpack theory.

Deeper incision typically involves more water and/or more flow events. If the mantled unit is the source of the liquid for the gullies, then it is expected that locations with evidence of larger or more frequent flows would be associated with regions of less mantled unit. It is unknown whether the mantled unit can insulate the surface sufficiently to allow temperatures and pressures appropriate for liquid water formation. An answer to this awaits future modeling of snowpack under Martian conditions.

Within the subimage, channels can clearly be seen to originate at a variety of layers. Also noticeable is the smooth, mantled material located between layers above these gullies.

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.