The Moon is a dead and dusty ball of rock. But it's also got a surprising amount of water, whether that's in the form of ice beneath its poles or in thin layers of gas above the surface.
The question that interests scientists is how it got there in the first place.
Previously it had been supposed that the water might have been carried to the moon on a comet or meteorite.
Now we might have a new take on an answer: the Sun.
Researchers at the Sorbonne Universités, Muséum National d'Histoire Naturelle, suggest that particles from the sun might be able to interact with dust particles on the Moon and great water.
The study said that lunar soil buffeted by the solar wind has less oxygen in it - and that the oxygen was probably used up by a reaction with particles from the sun. The result? Water, in small amounts in dust on the surface.
In a neat detail it turns out the study was completed using dust collected by the Apollo landings - it's still the only testable sample we have.
It's an interesting theory - unfortunately it's only half the story. The researchers admit the water beneath the Moon's surface is still a mystery, and a comet is still a pretty good answer for how it got there.