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This back and forth comparison shows changes that occurred in a gully on a south-facing slope in middle southern latitudes of Mars. Such changes in gullies on Mars, unlike changes in a recently discovered class of active slope features, have not been linked to warm seasons.

Both images in this pair were taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter, one on June 24, 2011, the other on July 29, 2009. In the later image, darkening of ground is visible near the tip of the gully in the lower left corner. The site is at 38.8 degrees south latitude, 159.5 degrees east longitude.

The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the spacecraft development and integration contractor for the project and built the spacecraft.