For years, scientists have assumed that the interior of the Moon is dry. However, a new study of satellite data has located numerous volcanic deposits around the moon – which could indicate large quantities of water trapped beneath its surface. The study, published in Nature Geoscience, explains that the ancient deposits are believed to be glass beads formed by the explosive eruption of magma from the deep lunar interior. As a result of this discovery, scientists are formulating a new opinion that the lunar mantle is actually water-rich.
The study was led by Ralph Milliken, an associate professor in Brown University’s Department of Earth, Environmental and Planetary Sciences. He said of the findings, “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. 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 detect the water content of the lunar volcanic deposits, scientists used orbital spectrometers to measure the light that bounces off a planetary surface. After collecting that data, they took into account the wavelengths of light which are absorbed or reflected by the surface to get an idea of which minerals and other compounds may be found in the rock’s interior. One challenge was taking into account the rising surface temperatures over the course of a day.
Using the new thermal correction, the scientists were able to find evidence of water in almost all of the pyroclastic deposits that had been previously mapped across the Moon’s surface. Such deposits include the Apollo 15 and 17 landing sites. “The distribution of these water-rich deposits is the key thing,” said 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.”
Now that evidence has been obtained suggesting that the interior of the Moon is water-rich, theories about its formation are evolving. Scientists presently believe the moon formed from debris left behind after an object about the size of Mars slammed into the Earth early in the solar system’s history. However, the original theory assumes that the Moon’s interior was dry. “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 co-author Shuai Li, a postdoctoral researcher at the University of Hawaii and a recent Brown Ph.D. graduate. “The exact origin of water in the lunar interior is still a big question.”
The finding has huge implications for future lunar exploration. The volcanic beads don’t contain a lot of water, but the deposits are large, meaning the H2O could be extracted. Said 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.”