"Solar wind is a flow of particles continually flowing away from the sun," says Nick Collins at The Telegraph. Earth’s magnetic field typically deflects these particles away, but the moon doesn’t have the same kind of protection. Solar wind “whacks into the lunar surface” at approximately a million miles per hour, often carrying hydrogen with it, says AFP.
The impact is “so brutal” that the sun’s gust diminishes the moon’s mass by a million tons per hour. Although it’s unclear exactly how the next step happens, the foreign hydrogen then combines with the moon’s oxygen to form hydroxyls, or tiny glassy, bead-like compounds comprised of one oxygen atom and one hydrogen atom, says Irene Klotz at Discovery News. These hydroxyls, which Liu and his team discovered using new soil analysis techniques, get stored in the soil and are just one hydrogen atom away from becoming water.
Where did the water on the moon come from?