Ice collects in the polar regions because Mars' rotation axis tilts about 25° to its orbit around the Sun. This gives Mars four distinct seasons, similar to those on Earth. But polar winters on Mars are much colder (–153° Celsius or –243° Fahrenheit) than the coldest winters on Earth.

Why does Mars have ice caps?

Like Earth, Mars has ice caps at its poles. ... During winter at each pole, temperatures are so low that carbon dioxide freezes from the atmosphere and forms additional layers of "dry ice." Much water is also trapped as permafrost surrounding the polar regions.

What would happen if we melted Mars ice caps?

That research used gravitational data about Mars collated by NASA from several of its missions to the Red Planet. But by this technique, too, the region comes up chock-full of water ice — enough that if you melted it down and spread it evenly around the planet, it would flood Mars by about 5 feet (1.5 meters).