Large amounts of water have been found trapped in volcanic deposits across the surface of the moon, which means the lunar mantle is probably a far wetter place than anyone ever thought possible. The finding could call into question our theories about the moon's formation, but it could also make future moon colonies more feasible, reports Phys.org.
The leading theory for how the moon formed is that it represents debris left behind after a catastrophic collusion between the young Earth and a Mars-sized planet very early in the solar system history. A collision like this should have burned off most of the moon's hydrogen, an essential ingredient for making water, so scientists have long assumed that the moon was a dry place.
Clues to the moon's hidden water were first revealed back in 2008, when a research team detected trace amounts of water in some of the volcanic glass beads brought back to Earth from the Apollo 15 and 17 missions. Then, in 2011, the water in those glass beads was further analyzed, revealing that the samples contain similar amounts of water as some basalts on Earth.
Could the moon's interior therefore contain similar amounts of water as found on Earth's?
What we know from Apollo
"The key question is whether those Apollo samples represent the bulk conditions of the lunar interior or instead represent unusual or perhaps anomalous water-rich regions within an otherwise 'dry' mantle," explained Ralph Milliken, lead author of the new research. "By looking at the orbital data, we can examine the large pyroclastic deposits on the moon that were never sampled by the Apollo or Luna missions. The fact that nearly all of them exhibit signatures of water suggests that the Apollo samples are not anomalous, so it may be that the bulk interior of the moon is wet."
To reach their conclusions, Milliken and co-author Shuai Li used a new thermal correction method to analyze the temperature profile of the areas of interest on the moon's surface. The source data came from the moon Mineralogy Mapper, an imaging spectrometer that flew aboard India's Chandrayaan-1 lunar orbiter. Temperature profiles can reveal which minerals and other compounds are present on the surface of the moon because wavelengths of light are absorbed or reflected by the surface differently depending on what it's made up of.
Water was found in nearly all of the large pyroclastic deposits that were mapped. Because these regions were distributed across the lunar surface, it means the detection of water in the Apollo samples was no anomaly. It also indicates the high likelihood that a similar distribution can be found in the moon's mantle.
If there is (or was) more water, how did it get there?
"The growing evidence for water inside the moon suggest that water did somehow survive, or that it was brought in shortly after the impact by asteroids or comets before the moon had completely solidified," said Li. "The exact origin of water in the lunar interior is still a big question."
It might mean that we need to re-formulate our theories about how the moon formed, or at least re-consider how hydrogen might survive under such extreme conditions. There's also potentially more than enough water to make mining operations on the moon worthwhile. Future moon inhabitants might get enough water from the moon to survive on their own without supplies from Earth.
"Anything that helps save future lunar explorers from having to bring lots of water from home is a big step forward, and our results suggest a new alternative," said Li.