Hi All

The recent null result for large ice deposits doesn't mean the Moon is dry or even much drier than if there were ice drifts. What it does mean is that the lunar water-holding regolith has been "farmed" time and time again by small impacts, and hence evenly mixed into the regolith. The water itself doesn't even have to come from comets - solar-wind implanted hydrogen can react with oxygen-bearing compounds in the soil and snatch away oxygen to make water molecules. These then bounce all over the Moon, gradually losing energy as they impact colder-terrain. Eventually they end up stuck at the poles. A very thin frost will form in the dark basins of polar craters, to be buried by the next load of soil cast out by a small impactor. But such frost is also broken up and mixed in with the soil by closer impactors, hence the deposits aren't thick layers of ice, but fragments mixed in with the regolith.

This theory was presented in a recent issue of "American Scientist", but I can't find a link to it in the text archive at the web-site.

Adam