Current studies suggest that the Martian polar ice caps are made up mostly of frozen carbon dioxide, also known as “dry ice.” Some frozen water, or just plain ice, may also be imbedded within the polar caps. Because of the atmospheric conditions on the surface of Mars, however, neither the ice nor the dry ice would melt to make water or liquid carbon dioxide when the temperatures go up; rather, they would sublimate, or turn directly into gas. So, unlike here on Earth, the polar ice caps on Mars are not a source of liquid water.