In the next weird thing found on -- or below -- the Red Planet, a ground-penetrating radar on board the Mars Reconnaissance Orbiter has found vast glaciers under the rocky surface. These glaciers are at the bases of mountains and cliffs, and are covered with rubble that may be protecting them from sublimating away. The even cooler thing is that these are at lower latitudes (nearer the Equator) than ever seen before.

"Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that is not in the polar caps," said John W. Holt of the University of Texas at Austin, who is lead author of the report. "Just one of the features we examined is three times larger than the city of Los Angeles and up to one-half-mile thick. And there are many more. In addition to their scientific value, they could be a source of water to support future exploration of Mars."

I still advocate going to the Moon for a while before heading off to Mars, but Mars does have one big advantage: that water locked up in the glaciers is not that hard to tap into. It can be used for drinking, farming, breathing, and even as protection from solar radiation (the hydrogen in water makes a pretty good radiation shield). These underground glaciers also answer a question that's puzzled scientists for years: the existence of aprons, or gently sloped regions surrounding tall features on Mars. Now it seems clear that the ice at the base of these cliffs and mountains lubricated rubble descending from higher up, so instead of getting big piles, the rubble forms a smoother decline. The radar reflections from aprons indicates they are indeed a thin layer of rubble on top of thicker ice. We've known for decades that Mars has water ice. What we're learning now is the extent of it, how deep it goes, how it's placed across the surface, and even how wet Mars was in the past. All of this builds us a picture of a once-dynamic planet, and one that still has lots of surprises waiting for us, literally just below the surface.

This older image shows a glacier that flowed from one Martian crater at the base of a mountain to another crater. Courtesy ESA/DLR/FU Berlin (G. Neukum).