As a rule, the truly large deposits of ice on Mars are at the poles... right? No. Researchers using the Mars Reconnaissance Orbiter's ground-penetrating radar have discovered that the planet's Utopia Planitia basin is hiding a thick (260 to 560 feet) ice sheet larger than the state of New Mexico. It's at least 50 percent pure, too. Observers had long suspected that the area had water thanks to surface cracking and depressions, but the previous explorer, the Mars Odyssey spacecraft, couldn't study much deeper than the surface.