Every winter, Mars’ polar region is covered with a layer of seasonal carbon dioxide ice (dry ice). In the spring jets of gas carry dust from the ground up through openings in the ice. The dust gets carried downwind by the prevailing wind and falls on top of the seasonal ice layer in a fan-shaped deposit.

Many jets appear to be active at the same time since numerous fans are all deposited in the same direction: this image is an example of such an occurrence. At the top of this image the fans are oriented in one direction while at the bottom they are going in a different direction. This suggests that as the ice layer thins, a set of gas jets becomes active, they die down, then further away another set starts up at a later time with a different prevailing wind direction.

Written by: Candy Hansen

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.