Mars has a seasonal southern polar cap composed of carbon dioxide (CO2, commonly known as dry ice), that overlies a permanent polar cap which is a mixture of CO2 ice, water ice and dust. As the CO2 evaporates in the spring the escaping gas carves channels in the permanent cap below. Often these channels radiate outward (or converge inward), giving them a spider-like appearance.

In this false color image the seasonal frost is whitish-lavendar (1507x1179; 5 MB). The tan areas starting to show through are where the frost has already evaporated (sublimated is actually the correct term, when ice changes directly to a gas). Tan-colored dust blows around and accummulates in the bottom of some of the channels.

This is truly other-worldly terrain, with exotic landforms with no earthly analogs.
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.