... Mars . ... Mars' northern polar regions in transition . Studies show that the North Polar Cap is covered by frozen water and carbon dioxide ice in winter and spring, but the carbon dioxide ice warms and evaporates into the atmosphere during the Red Planetт??s summer. ... All the carbon dioxide ice has gone, leaving just a bright cap of water ice. ... These processes bear witness to a dynamic water cycle on Mars and may lead to the varying accumulation of water ice over the polar cap. ...