Waxing and Waning Winds
The Hellespontus Montes is a rugged mountain range located on the western rim of one of the largest impact basins in the Solar System: Hellas Basin.
The 7-kilometer depth of Hellas and its location in the Southern Hemisphere form an active atmospheric system that directly impacts local landscape evolution. Hellespontus has a large accumulation of sand dunes and other wind-created bedforms that have been migrating on a continual basis since HiRISE began imaging Mars.
A dune's steepest area, called a "slip face," indicates the down-wind side of the dune and its migration direction as driven by local winds. At this location, there are many dunes influenced by eastward winds that were draining into Hellas. Meanwhile, other locations show that migration had shifted towards the opposite direction to the west.
In certain cases, we see these opposing dune directions in proximity. The complex patterns are not due to winds that are constant in magnitude or direction, but rather they wax and wane over the course of the Martian year.
The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. (The original image scale is 51.0 centimeters [20.1 inches] per pixel [with 2 x 2 binning]; objects on the order of 153 centimeters [60.2 inches] across are resolved.) 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.