This HiRISE image shows a bright gully deposit and other gullies within a crater wall in Terra Sirenum (37.7 degrees south, 229.0 degrees east).

Three images are available: A) The full frame HiRISE image, with the crater at left center; the width of the image is 6 km; B) enlargement showing the crater (895 x 1296; 3MB); and C) a close-up of the bright gully deposit (1120 x 809; 884KB). Frames B and C have been stretched to enhance contrast. The red box in B shows the location of C.

As seen in A and B, the appearance of the crater wall differs between the northern and southern sides. On the northern pole-facing side walls, prominent gullies with channels and aprons are apparent, with many of these having valley-like alcoves near their tops. The morphology of the gullies is consistent with formation by a fluid, most likely water. On the pole-facing slopes, ground ice or aquifers may be more stable, being subjected to less heating from sunlight compared to equator-facing slopes. In contrast, the southern, equator-facing walls are dominated by rocky debris flows that lack prominent channels.

The bright gully deposit has a very fluid-like appearance, and has not been covered by other gullies or debris flows, indicating a young age. The brightness is a mystery; it could be due to minerals formed from water or ice. Alternatively, the flow that made the gully may have removed a thin coating of relatively darker dust and soil, revealing a brighter substrate. In any case, this feature is probably indicative of recent flow of water or water-rich material on Mars.

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.