This caption is part of a December 2007 AGU presentation "Spring at the South Pole of Mars."

The south polar region of Mars is covered every year by a layer of carbon dioxide ice. In a region called the "cryptic terrain," the ice is translucent and sunlight can penetrate through the ice to warm the surface below.

The ice layer sublimates (evaporates) from the bottom. The dark fans of dust seen in this image come from the surface below the layer of ice, carried to the top by gas venting from below. The translucent ice is "visible" by virtue of the effect it has on the tone of the surface below, which would otherwise have the same color and reflectivity as the fans.

Bright streaks in this image are fresh frost. The CRISM team has identified the composition of these streaks to be carbon dioxide.

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.