Credit: NASA/JPL/UNIV. ARIZONA

Channels carved by vaporizing carbon dioxide splay across the south polar region of Mars in this image taken by the Mars Reconnaissance Orbiter.

Last week, at the American Geophysical Union meeting in San Francisco, project scientists reported that the channels probably form as the warmth of spring causes carbon dioxide in the soil to vaporize, then flow upwards and burst out like geysers. Some of the gas then rapidly freezes and falls back to the ground in a brilliant white frost pattern. The strange features, radiating out from the top of small hills, were snapped during the martian spring in March.