Water on Mars has been a given since the 1970s, when spacecraft returned images of great flood channels formed in middle Mars history, several billion years ago, as well as delicate filigreed networks of narrow valleys from the planet's earliest days. But decades later, researchers are still trying to figure out how water could have carved those features on a planet that now locks up all its water in ice. At the meeting, researchers introduced yet another water puzzle: a small area that appears to have been scoured by torrential rainstorms during the planet's latter days of extreme cold and ice. "I haven't seen anything like it elsewhere on the planet," says Mars geologist James Zimbelman of the Smithsonian National Air and Space Museum in Washington, D.C. "The implications are mind-boggling."
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