The Moon's status as a "dry" rock in space has long been questioned. Competing theories abound as to the source of the H20 in the lunar soil, including delivery of water to the Moon by comets.

This week, Tartese et al announced in Geology that new analyses of lunar soil samples demonstrates that basalts from the Moon's mantle contain hydrogen from water indigenous to Earth.

According to the authors, their work is "challenging the paradigm of a "dry" Moon, and arguing that some portions of the lunar interior are as wet as some regions of the Earth's mantle."

The Moon's origin is believed to be the Earth itself, which gave rise to the Moon when a Mars-sized object impacted our planet around 4.5 billion years ago. The Earth's mantle is known to be partially water.

These latest finding raise the odds that the Moon may have a partly-aqueous core today. These results promise that at some time in the past there was water in the Moon's mantle, inherited from an ancestral proto-Earth, which rose to the surface in magma, and became trapped in crystals called apatites.

How much water remains, and how it can be accessed to support human habitation, will be a subject of ongoing study.

The paper, "Apatites in lunar KREEP basalts: Astrobiology Magazine
to understanding the H isotope systematics of the Moon," was published in the journal Geology under lead author Romain Tartese

NASA | Water on the Moon Video Presentation