What We Know About Water Discovery on the Moon

Water has been found hidden inside tiny glass beads taken from the surface of the moon by China's Chang'e 5 mission

In a paper published Monday in the journal Nature Geoscience, scientists describe how these glass beads, which returned from the moon in late 2020, are only around a hair's breadth wide, at between 50 micrometers and 1 millimeter. The water content makes up only a tiny fraction of the beads' volume.

The scientists also said there could be as much as 330 billion tons of water hidden inside these glass beads across the entire moon's surface.

Originally, it was assumed that the moon had no water at all since no water had been detected in the soil samples brought back by the Apollo missions. Now, however, water has been known to exist on the moon for decades. Water ice at the poles was discovered in the 1990s using the neutron spectrometer on board the Lunar Prospector mission, and water ice was later found inside multiple craters across the moon's surface.

In 2018, NASA's Moon Mineralogy Mapper, carried by the Indian Space Research Organization's Chandrayaan-1, gave researchers the first high-resolution map of the minerals that make up the lunar surface. It showed water clustered at the poles.

"Today, there is little doubt that most of the moon's surface harbors water in one form or another," the authors wrote in the Nature Geoscience paper.

These glass beads, however, contain water that wasn't originally on the moon. Instead, the beads and the water within them were formed as a result of impacts from meteorites at immense speeds. During the collision, the beads formed when silicate minerals were heated to scorching temperatures by the meteor's impact, melting and forming molten balls of glass-like material.

Within these molten glass beads of moon rock, the oxygen from the rocks reacts with the hydrogen ions in the solar wind plasma washing over the moon at all times, forming H2O, or water, which is sucked into the beads. These beads are then scattered across the moon's surface and left for millions of years, buried beneath the dust.

The paper's authors wrote: "A recent geochronological study of CE5 [Chang'e 5] impact glass beads has shown that they formed more or less continuously for the past 2 Gyr [2 billion years], with prominent peaks in formation ages at [around] 575 million years ago (Ma), 380 Ma, 68 Ma and 35 Ma."

Previously, surface water on the moon was seen coming and going in diurnal cycles, being lost to space. Therefore, researchers concluded there had to be a hydrated layer in the lunar soil to somehow replenish this lost water, but it was not found until now.

The study also found that water in the solar wind can take between one and 15 years to diffuse into the glass beads at temperatures of 360 Kelvin (188.33 F) and that the beads are also capable of releasing the water into the environment. This, the authors say, may suggest that these beads are important in sustaining the lunar surface's water cycle.

The scientists hope that this water could one day provide a water source for lunar missions, as they think that extracting the water from the multitudinous beads might be fairly easy.

"If we want to extract the water in impact glass beads for future lunar exploration, first we collect them, then boil them in an oven and cool the released water vapor. Finally, you will get some liquid water in a bottle," Sen Hu, a planetary geologist at the Chinese Academy of Sciences' Institute of Geology and Geophysics and a co-author of the paper, told Live Science.

"Another benefit is that impact glass beads are [common] in lunar soils, from equator to polar and from east to west, globally and evenly," Sen said.

This could be invaluable to upcoming manned missions to the moon as well as planned lunar bases forecast to be built in the near future. The China National Space Administration plans to complete a base on the moon by 2029, with NASA following close on its heels.

However, Ian Crawford, a professor of planetary science and astrobiology at Birkbeck, University of London, told The Guardian that the amount of water on the moon wasn't much by Earth standards. Each cubic meter (35.3 cubic feet) of moon soil contains at most 130 milliliters of water (4.4 fluid ounces).

The paper also suggests that these kinds of glass beads with water trapped within may be common to other airless planets where the solar wind can react with the rocks thrown up during meteor collisions.

"Our direct measurements of this surface reservoir of lunar water show that impact glass beads can store substantial quantities of solar wind-derived water on the Moon and suggest that impact glass may be water reservoirs on other airless bodies," the paper's authors wrote.

They continued: "The presence of water, stored in impact glass beads, is consistent with the remote detection of water at lower-latitude regions of the Moon, Vesta and Mercury. Our findings indicate that the impact glasses on the surface of Solar System airless bodies are capable of storing solar wind-derived water and releasing it to space."

These beads therefore could provide a water source for future missions to these other astronomical bodies.

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