Mercury Harbors Lots of Ice

Just in time for Christmas, scientists have confirmed a vast amount of ice at the north pole—on Mercury, the closest planet to the sun. The findings are from NASA's Mercury-orbiting probe, Messenger, and the subject of three scientific papers released today by the journal Science. The frozen water is located in regions of Mercury's north pole that always are in shadows, essentially impact craters. It's believed the south pole harbors ice as well, though there are no hard data to support it. Messenger orbits much closer to the north pole than the south.

"If you add it all up, you have on the order of 100 billion to 1 trillion metric tons of ice," says one scientist. "The uncertainty on that number is just how deep it goes." The water almost certainly came from impacting comets, or possibly asteroids. Columbia University's Sean Solomon stressed that no one is suggesting that Mercury might hold evidence of life, given the presence of water. But the latest findings may help explain how water and other building blocks of life arrived elsewhere in the solar system. (More Mercury stories.)