Several years ago gullies carved into hill-slopes and the walls of impact craters like the ones pictured here were discovered. Scientists are excited to study these features because, on Earth, they usually form through the action of liquid water - long thought to be absent on the Martian surface. Whether gullies form under today's cold dry conditions is a major question that planetary scientists are trying to answer.

The gullies pictured here are great examples of what a typical Martian gully looks like. You can see wide V-shaped channels running downhill (from top to bottom) where the material that carved the gully flowed. At the bottom of the channel this material empties out onto a fan-shaped mound. Several gullies are visible here and the fans from each gully overlap one other in complicated ways.

At the tops of the channels, large amphitheater-shaped alcoves are carved in the rock. The material removed from these alcoves likely flowed downhill to the aprons through the gullies.

Gullies at this site are especially interesting because scientists recently discovered examples at similar locations to be still active. Images separated by several years showed changes in the appearance of some of these gullies. Today, planetary scientists are using the HiRISE camera to examine gullies for ongoing change and investigate what that might mean for the occurrence of liquid water on the surface of Mars.

Written by: Shane Byrne

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.