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Trillions of pounds of water may be strewn across the moon, trapped in tiny glass beads that could have formed when asteroids struck the lunar surface, according to a new study.
The findings, laid out in a study published Monday in the journal Nature Geoscience, were pieced together by scientists in China who analyzed the first lunar soil samples to be returned to Earth since the 1970s.
The research points to an answer for a question scientists have been pondering for years as they’ve attempted to pin down exactly how water is stored on the moon — especially in regions outside the lunar poles, where water ice may exist in greater abundance.
“To sustain a water cycle at the surface of the Moon, there should be a hydrated layer (reservoir) at depth in lunar soils,” according to the study. “However, finding this water reservoir has remained elusive, despite several studies having investigated the water inventory of fine mineral grains in lunar soils.”
The authors of the latest study set out to identify a potential water reservoir by further investigating the glass beads formed during impact by asteroids. And the team found the tiny glass objects were embedded with substantial amounts of water.
A look at the study
The lunar soil sample analyzed for this study was collected by China’s Chang’e-5 mission, which made a soft landing on the moon’s Earth-facing northwest corner and carried regolith samples back home in 2020.
From those samples, researchers from several institutions in China, including Nanjing University and the Chinese Academy of Sciences, handpicked 150 grains to study, ranging in size from about 50 micrometers — or the width of a human hair — to about 1 millimeter.
The theory proposed by this latest research is that these glass beads, formed in ancient times, can be imbued with water when they’re hit with solar winds, which carry hydrogen and oxygen from the sun’s atmosphere across the solar system. In fact, it could be how more than 270 trillion kilograms (600 trillion pounds) of water is stored across the moon.
“We found a new mechanism that solar-wind hydrogen can diffuse into the glass beads and thus identified a new water reservoir on the Moon,” Hejiu Hui, one of the study’s coauthors and a researcher at Nanjing University, said via email. “On the other hand, impact glass beads are distributed in the regolith globally on the Moon. Therefore, the impact glass beads can be replenished with water on the Moon’s surface and can sustain the lunar surface water cycle.”
The beads can be replenished with water every few years, the study suggested.
The findings build on research from NASA that suggested water is present on the sunlit side of the moon. Scientists have been searching for more information about how that water was stored. (One study that was published in 2020 — which relied on data collected by NASA’s Stratospheric Observatory for Infrared Astronomy airborne telescope, or SOFIA — suggested the water detected on the moon’s surface was stored in glass.)
NASA did not immediately respond to a request for comment about this study. The space agency hasn’t been permitted to work with its Chinese counterparts since 2011, when Congress passed the Wolf Amendment.
Understanding how water is stored on the moon is useful, Hui noted, because it could point future lunar astronauts toward potential resources that could one day be converted to drinking water or even rocket fuel.
“This water can be released by just simply heating these glass beads,” Hui said.
Putting it in perspective
Dr. David Kring, a principal scientist at the Lunar and Planetary Institute in Houston, said this research gives scientists new insight into how water can be stored on the moon, particularly in locations similar to the Chang’e 5 mission’s landing spot on the nearside of the moon. He was not involved in the study.
“That’s important for scientific discussion of lunar water cycles on the moon,” he noted.
But, Kring said, there are likely better places for astronauts to harvest water for practical purposes, “which is why we’re interested in the lunar poles.”
Scientists have theorized there may be large deposits of water ice at the moon’s poles since the Apollo era. And NASA plans to send astronauts to explore the area as part of its Artemis program, which aims to send humans to the lunar south pole later this decade.
“I think the international interest in exploration of the moon will fuel everybody’s interest,” Kring said. “I cannot wait until we have Artemis astronauts in the lunar south polar region in two to three years.”