Dry Ice Pits on Mars . ... Credit Copyright: HiRISE , MRO , LPL (U. Arizona) , NASA Explanation: Part of Mars is defrosting. Around the South Pole of Mars, toward the end of every Martian summer, the warm weather causes a section of the vast carbon-dioxide ice cap to evaporate. Pits begin to appear and expand where the carbon dioxide dry ice sublimates directly into gas. ... The HiRISE camera aboard the Mars-orbiting Mars Reconnaissance Orbiter captured the above image in late July. ...