Like on Earth, Mars has permanent Northern and Southern water ice caps. Both caps are covered during the Martian winter season with varying depths and layers of carbon dioxide (CO2) ice sheets. On Earth, we most commonly call frozen CO2, “dry ice”. It is the same stuff commonly put into punch bowls during Halloween celebrations that makes it bubble, churn and “smoke” as it melts away.
During the Martian Spring and Summer seasons, the CO2 sheeting of the Northern hemisphere melts away (more on the spectacular mechanics of this event in another post) leaving the water perma-cap exposed. In the Southern hemisphere, the CO2 ice sheeting rarely (if ever) melts away completely, leaving the Southern water ice cap perpetually covered by a layer of dry ice.
The Northern Martian ice cap is estimated to contain 821,000 cubic kilometers of water, while less is yet known about the total volume of water of the Souther ice cap. However, it is expected that the Southern ice cap will contain significantly less volume of water, as the cap itself is significantly smaller in size compared to the Northern ice cap.
Below is a mosiac image released by the ESA (European Space Agency) of the Northern ice cap captured by their Mars exploration mission, Mars Express:
Here is what NASA has to say about the top image:
"LAYER CAKE. Climatic cycles of ice and dust built the Martian polar caps, season by season, year by year — and then whittled down their size when the climate changed. Here we are looking at the head of Chasma Boreale, a canyon that reaches 570 kilometers (350 miles) into the north polar cap. Canyon walls rise about 1,400 meters (4,600 feet) above the floor. Where the edge of the ice cap has retreated, sheets of sand are emerging that accumulated during earlier ice-free climatic cycles. Winds blowing off the ice have pushed loose sand into dunes, then driven them down-canyon in a westward direction, toward our viewpoint."
Top image credit: NASA/JPL/Arizona State University, R. Luk