NASA has chosen the final destination for the LCROSS lunar impacting probe: the crater Cabeus A
, near the Moon’s south pole.
So why is NASA smacking a probe into the Moon at high speed, and why there?
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.
Detecting that water is tough. Radar results have been inconclusive, with some people saying there’s lots of water, and others saying there’s none at all. By impacting a probe there, any ice located at the impact site will be shot up above the lunar surface, where sunlight will break it up into H+ and OH- molecules, which can be detected. Thus, LCROSS. I have a more detailed description of all this in an earlier blog post about LCROSS
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. Here’s a map of the area