Recent Gullies in Equatorial Valles Marineris
Although actively-forming gullies are common in the middle latitudes of Mars, there are also pristine-looking gullies in equatorial regions.
In this scene, the gullies have very sharp channels and different colors where the gullies have eroded and deposited material. Over time, the topography becomes smoothed over and the color variations disappear, unless there is recent activity.
Changes have not been visible here from before-and-after images, and maybe such differences are apparent compared to older images, but nobody has done a careful comparison. What may be needed to see subtle changes is a new image that matches the lighting conditions of an older one. Equatorial gully activity is probably much less common — perhaps there is major downslope avalanching every few centuries — so we need to be lucky to see changes.
MRO has now been imaging Mars for over 16 years, and the chance of seeing rare activity increases as the time interval widens between repeat images.
The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. (The original image scale is 26.5 centimeters [10.4 inches] per pixel [with 1 x 1 binning] to 53.1 centimeters [20.9 inches] per pixel [with 2 x 2 binning]) North is up.
The University of Arizona, in Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.