Since the presence of water on the Moon has been confirmed. scientists have been trying to figure out where the water originated. Now, they think a large percentage of it might have come in on the solar wind.
Comets smashing into the Moon have no doubt brought some water, but researchers studying Apollo 11 regolith samples that were gathered by Neil Armstrong found an isotope of hydrogen in tiny glass beads. That isotope is associated with the Sun, so they asume it and water molecules reached the Moon in the solar wind.
If the theory is correct, it could mean water exists on other airless worlds throughout the Solar System. That, in turn, could be good news for human exploration.