This image from NASA's Mars Reconnaissance Orbiter includes an especially long example of a type of dark marking that advances down some Martian slopes in warmer months and fades away in cooler months.

This image includes an especially long example of a type of dark marking that advances down some Martian slopes in warmer months and fades away in cooler months.

The features, called "recurrent slope linea," may be seasonal flows of salty water. Red arrows indicate the location of one on this image taken by the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter. This one is three-quarters of a mile (1.2 kilometers) long.

HiRISE is one of six instruments on NASA's Mars Reconnaissance Orbiter. The University of Arizona, Tucson, operates the orbiter's 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 in Pasadena, manages the Mars Reconnaissance Orbiter Project for the NASA Science Mission Directorate, Washington.

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