It stays frozen only thanks to a thick layer of dust.
Underneath its red, rusty exterior, it seems Mars has a cold heart of ice. Researchers from the Niels Bohr Institute used radar measurements from NASA's Mars Reconnaissance Orbiter and found that Mars has several glacier belts of water ice under a layer of dust. Together, they hold over 150 billion cubic-meters of ice.
Evidence of Mars once having water is written all over the planet's face. The first significant finding of NASA's Curiosity rover was an ancient creek bed back in September 2012 and, a year later, the agency reported thatthere was water locked in the Martian soil—about two pints of water for every cubic-foot of soil. Just a year ago, Spanish researchers found evidence of glaciers moving through Mars's Gale Crater some 3.7 billion years ago or so, when some believe the surface of Mars had lakes. The planet is covered with water's chemical signature and, as it turns out, Mars is still also covered with camouflaged ice.
Scientists have known that there's some kind of glacial activity going on just below the Martian surface, but they weren't sure if the thousands of glacier-like formations were made of frozen-water ice, dry ice, or just mud.
But thanks to a combination of observation and modeling, it looks like Mars is belted with glaciers of ice—a whole lot of ice. Enough ice to encase Mars with over a meter of the stuff.
"We have looked at radar measurements spanning ten years back in time to see how thick the ice is and how it behaves,"study author Nanna Bjørnholt Karlsson said in a press release. "A glacier is after all a big chunk of ice and it flows and gets a form that tells us something about how soft it is. We then compared this with how glaciers on Earth behave and from that we have been able to make models for the ice flow."
The Copenhagen-based researchers note that the glacier belts are located in both north and south hemispheres, "between the latitudes 300-500—equivalent to just south of Denmark's location on Earth."
The thick layer of dust that covers the glaciers keeps the ice from turning into water vapor in Mars's low-pressure atmosphere, which is good news for anyone who, I don't know, is on Mars and gets thirsty, if that ever happens.