<P> The caps at both poles consist primarily of water ice . Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only , while the south cap has a permanent dry ice cover about 8 m thick . The northern polar cap has a diameter of about 1000 km during the northern Mars summer , and contains about 1.6 million cubic km of ice , which if spread evenly on the cap would be 2 km thick . ( This compares to a volume of 2.85 million cubic km ( km ) for the Greenland ice sheet . ) The southern polar cap has a diameter of 350 km and a thickness of 3 km . The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km . Both polar caps show spiral troughs , which recent analysis of SHARAD ice penetrating radar has shown are a result of roughly perpendicular katabatic winds that spiral due to the Coriolis Effect . </P>
what is the snow on mars made of
water ice Frozen carbon dioxide