HiRISE image PSP_001508_1245 covers a portion of a sinuous ridge on the floor of Argyre Basin in the southern hemisphere of Mars (55.0 degrees south, 319.2 east).

The ridge is one of a number of similar ridges that split and rejoin as they wind across the floor of the basin and around hills and mountains. It is unclear what process is responsible for formation of the ridges, but glacial, coastal, and fluvial processes have all been suggested.

For example, they may represent ancient coastal shorelines, sediments deposited in a river flowing under glacial ice, or an ancient river bed that has been left standing in relief as surrounding, probably finer grained sediments were subsequently eroded away.

The HiRISE image shows that the sediments forming the ridge include many large boulders that are often 1-2 meters or more in diameter. In addition, the sediments appear to occur in crude layers in a few locations. Such characteristics hold important clues to the process(es) responsible for formation of the ridge.

For example, if the ridge is the deposit formed by an ancient river then it may be difficult to account for the transport of so many large boulders.
Written by: John Grant

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.