We know there's water frozen on the Moon — and we now know there's plenty more water elsewhere in the solar system: http://io9.com/5827649/a-map-of-all-the-water-in-the-solar-system

So how did it all get there? It might well be the Sun that's behind it all.

That's the conclusion of a new study from researchers at the University of Michigan, University of Tennessee, and the California Institute of Technology. We know water and its associated compounds is found not only in the Moon's hidden craters but also throughout what's known as the lunar regolith. The regolith is a fine layer of all the powder and bits of rock that has accumulated on top of the Moon's surface over the eons.

While the quick and obvious explanation for all this water near the Moon's surface is that it all comes from comet impacts — and indeed, that's likely part of any explanation — the main driver behind the Moon's water supply might be something else. There's a decades-old theory that suggests the Sun could send out streams of ionized hydrogen atoms — protons, in other words — which could combine with oxygen found on the Moon's surface to form water and water-related compounds known as hydroxyls, which are composed of one oxygen atom and one hydrogen atom.