The moon may contain a lot more water than previously thought. But don't pack your swimsuit. It's preserved in tiny bits of volcanic rock trapped in crystals called melt inclusions.
Researchers used an ion microscope to measure seven samples of magma trapped within such crystals collected during the Apollo 17 mission in 1972, the last time humans set foot on the surface. The crystals were believed to have been created "within a matter of minutes after their eruption," the researchers say in their article in this week's edition of the journal Science Express.
The samples contain tiny bits of water that did not evaporate away because they were encased in crystals that protected them when volcanic eruptions brought them from the moon's depths to its surface eons ago. In fact, the researchers found up to 1,410 parts per million water, which is about 100 times more than anyone expected would be there.
There wasn't much water and nor many volatile elements in the inner solar system when Mercury, Venus and the Earth were being created. The fact that even smaller amounts were found on the moon has been thought to show that our satellite was formed by a high-temperature, "giant impact collision between a Mars-sized object and an early-formed proto-Earth," they write.
However the researchers suggest their findings could mean that the theory needs to be reevaluated. It could either be that the molten Earth and proto-moon exchanged more material during the collision than believed, or that parts of the lunar interior somehow escaped the widespread melting that happened afterwards.