http://blogs.discovermagazine.com/badastronomy/2006/04/10/lcross-to-impact-the-moon-look-for-water/
The idea is that over millions and billions of years, a lot of comets have hit the Moon. The water from these comets hits the surface and sublimates away… but if any settles at the bottoms of deep craters near the Moon’s poles, these permanently shadowed regions can act as a refrigerator, keeping the water from disappearing. It can stay there, locked up as ice, for a long, long time. Some estimates indicate there could be billions of tons of ice near the Moon’s south pole.
This water would make it a lot easier to place laboratories and colonies on the Moon; water is heavy and hard to transport via rockets, so finding some already there would save a huge amount of effort and, of course, cost. The problem is that the water was not directly detected, only hydrogen was. Confirming the existence of this water is a pretty big deal.
The choice of Cabeus A for the impact site is a good one. It’s near the south pole, it’s a likely spot for there to be ice under the surface, it’s on the near side of the Moon, so people back here on Earth can observe it, but close enough to the limb that any ejected water can be seen.
LCROSS is planned to impact the crater at 11:30 GMT on October 9, which is early morning for the U.S. (in fact, there will be two impacts; one from the spacecraft and another by the Centaur booster) The plume from the impact should stretch up many kilometers. It will almost certainly be too thin to be seen by amateur instruments, but the impact itself should make a bright enough flash to be seen if you have a telescope. The crater itself will be in shadow, making the light flash easier to spot. It’ll only last a second or two, so if you want to observe it, be prepared! NASA has a nice webpage with all the info you need to watch this historic event for yourself.
Buy your stunning LCROSS t-shirts here!
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