There's water on the Moon -- quite a lot, in fact. And even though you won't find a single cloud on the Moon, much of its water comes from a steady downpour: a "rain" of particles known as the solar wind.
KUHLMAN: That water is basically due to four and a half billion years of having solar wind hydrogen thrown at it.... Basically, the Moon is like the Earth -- it's a big ball of oxygen with a few impurities. So you've got lots of oxygen, but you can pull the hydrogen out of the regolith and make water.
Kim Kuhlman is a scientist at the Planetary Science Institute who's studying this process. It's one of several "space weathering" processes, which change the surfaces of the Moon and other airless bodies.
The solar wind is a steady flow of hydrogen and helium atoms and other particles from the surface of the Sun. When the hydrogen hits the Moon, it can bind with oxygen atoms to make water or related molecules. Spacecraft have discovered that there are lots of water molecules in the lunar soil, known as regolith.
Kuhlman is studying how this process works. Her results will help scientists interpret observations of the surface made by craft in lunar orbit. They may also help the scientists who study the Sun. And they could even help engineers figure out how to squeeze out the water and other useful compounds -- providing valuable resources for lunar colonists.
More about space weathering tomorrow.
Script by Damond Benningfield, Copyright 2009
Today's program was made possible in part by a grant from NASA.