This image features a series of long and somewhat linear ridges in the Huo Hsing Vallis region of Mars.

These ridges appear to be forming as a result of erosion of the surrounding rock. The ridges themselves are likely stronger that the surrounding rock and therefore stay behind as the remainder of the rock is whittled away, possibly by flowing water, blowing wind or a combination of both.

If water played a role in the erosion of the rock and exposure of these ridges, this water would have flowed many thousands or millions of years ago, perhaps through Huo Hsing Vallis. Water underground may also have helped to form these ridges prior to erosion. On Earth, water and other fluids flowing underground often follow cracks and faults, since it is easier for the liquids to flow through the open spaces of these fractures than through solid rock. These liquids often leave behind minerals within the fractures that help to strengthen the surrounding rock by essentially gluing the fragments of rock together. This can make the fracture stronger than the surrounding rock and lead to ridges that withstand the forces of erosion.

Similar “cemented” fractures have also been interpreted elsewhere on Mars, and if true, would be useful indicators of the presence of underground water at some point in the planet’s past.

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.