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Water in the Moon’s Interior

S u m m a r y :
Our moon’s interior contains a considerable amount of water—and this water, which might have originated from the moon itself, might possibly be harvested by lunar explorers. Or so says a new study published in the journal Nature Geoscience.

A ‘Watery’ Lunar Mantle

A team of researchers from Brown University have found water in the depths of several ancient volcanic deposits that are scattered all over the moon. Thank satellite data for the discovery! These deposits appear to have abnormally high quantities of trapped water as opposed to other regions of the moon. These new findings suggest that the layer beneath the crust of our satellite, that is the mantle which surrounds the outer core, has relatively large amounts of ‘lunar water’.

Ancient lunar volcanic deposits hint at the presence of large quantities of water in the lunar mantle. Photo credits: Olga Prilipko Huber.

Glass Beads in The Moon

The ancient deposits are thought to contain glass beads, the result of magma eruption stemming from the deeper lunar interior. These beads might be the secret to lunar water. However, it was once generally assumed that the interior of the moon was depleted of water. Then, later discoveries indicated that the volcanic beads might have traces of water; this finding was based on research carried out on beads brought from the moon from the Apollo 15 and 17 missions. Given that Earth basalts contained the life liquid because the planet’s mantle contained water, it was concluded that the moon’s mantle might also be containing water: a suspicion confirmed by a 2011 study as lunar glass beads were found to contain similar quantities of water as Earth basalts.

How Much Water in The Moon?

Now, the question has remained as to whether the Apollo samples are representative of the general conditions of the lunar interior or whether they only constitute unusual water distributions in a lunar mantle that would be otherwise dry, explains lead author Ralph Milliken.

Milliken together with his colleague, Shuai Li, used orbital instruments to detect the water content of the volcanic deposits of the moon: they investigated the wavelengths at which light rays were absorbed or reflected by the lunar surface, a variable used to determine the compounds present on a heavenly body.

The findings show the presence of water in most of the large known deposits. This data include the deposits in the vicinity of the Apollo missions landing site, from where the samples were taken.

“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,” says Milliken.

“The distribution of these water-rich deposits is the key thing,” explains Milliken. “They’re spread across the surface, which tells us that the water found in the Apollo samples isn’t a one-off. Lunar pyroclastics seem to be universally water-rich, which suggests the same may be true of the mantle.”

New Questions on Moon Formation

If the moon’s interior does contain a lot of water, we will be having to attend to further questions, specially those relating to its formation. The most common theory explaining the manner in which the moon came into being describes an impact onto Earth that scraped off portions of the latter’s surface. These were, then, sent into orbit, thereby becoming our moon. So, the moon would basically be debris from the Earth. This implies that the moon’s interior is dry because of the great un-likelihood of any hydrogen to have survived the high temperature of that crash. So, evidence of water in the moon’s interior raises questions about this theory.

“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,” says Li. “The exact origin of water in the lunar interior is still a big question.”

Harvesting Lunar Water

Another important conclusion is that this water, if it exists, might be harvested. While the volcanic beads contain only around 0.05% of water by weight, the deposits from where they come are large.

“Other studies have suggested the presence of water ice in shadowed regions at the lunar poles, but the pyroclastic deposits are at locations that may be easier to access,” explains Li. “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.”

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