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HONG KONG — As Chinese scientists analyzed the soil samples that their lunar probe brought back from the moon, they realized something groundbreaking: There was water found along with minerals in the soil.
NASA and Indian spacecraft have spotted what they believe to be water on the moon's surface, and Chinese scientists last year found water trapped in glass beads strewn across the moon.
But this latest discovery, scientists say, is the first time water in its molecular form, H2O, has been found in physical samples — and, importantly, it was retrieved from a part of the moon where they'd previously thought water in that form couldn't exist.
Researchers closely inspected samples collected by China's Chang'e-5 probe, which landed on the lunar surface in 2020, and found a "prismatic, plate-like transparent crystal" — roughly the width of a human hair — that was in fact an "unknown lunar mineral" dubbed ULM-1, according to the study, which published July 16 in the journal Nature Astronomy.
The ULM-1 crystal is made up of roughly 41% water, with bits of ammonia that keep the H2O molecules stable despite wild temperature swings on the moon, according to the study.
This type of water could be a potential "resource for lunar habitation," the scientists wrote in their study.
"The discovery of a hydrated mineral at the Chang'e-5 landing site is fascinating and will further enhance our understanding of rock-vapor reactions in the lunar crust and on the lunar surface," said David A. Kring, principal scientist at the Lunar and Planetary Institute in Texas, who was not involved in the study.
Tough to extract
There are three types of water that can exist on the moon, according to Yuqi Qian, a planetary geologist at the University of Hong Kong, who was not involved in the study.
There are water molecules, the compound we know as H2O; its frozen form, ice; and a molecular compound called hydroxyl, a close chemical relative.
Previous discoveries suggested that water had existed on the moon when volcanoes used to erupt in the ancient past — and that lunar water had come from those volcanoes, meaning it came from within the moon and has been present since the moon's early existence.
At times researchers had believed the moon was dry, particularly after not initially finding water in the samples collected by NASA's Apollo missions and the Soviet Union's Luna missions.
It was only in more recent years that scientists found water, ice and water molecules mostly located at the dark, cold lunar poles where the sun doesn't reach. A recent study has also suggested that water or hydroxyl may be trapped in glass beads strewn across the lunar surface, and that solar winds could transform hydroxyl to form water, or H2O.
Molecular water is "not stable in other regions of the moon," vaporizing at lower latitudes where temperatures can exceed 212 Fahrenheit, said Qian.
This new study changes that.
The samples, retrieved by China's Chang'e-5 probe, came from a middle-latitude part of the moon, at 43.1 degrees latitude — an area that's normally "not stable for molecular water," Qian said. Ammonium was found in the samples, which acted as a stabilizer for the water molecules, he explained.
This mechanism also corroborates NASA's findings from 2020, when its SOFIA telescope detected the signature of water on the lunar surface.
"I think it has lots of potential, this new finding that we can extract molecular water directly from lunar soils," Qian said. "I think this is a new mechanism to make molecular water stable on the lunar surface."
Kring caveated that though the sample was collected from a mid-latitude area, "it was not clear if it formed there. Impact processes can redistribute rock across the lunar surface."
China's space ambitions
A growing number of countries, including the United States, are eyeing the strategic and scientific benefits of expanded lunar exploration.
Understanding how water is stored on the moon is useful, experts have previously told CNN, because it could point future lunar astronauts toward potential resources that could one day be converted to drinking water or even rocket fuel.
Kring similarly cautioned that the findings so far have "no significant implications for exploration mission architectures, although it demonstrates that discoveries await those who are willing and able to explore the Moon."
China's rapid advancements have caught NASA's attention. The space agency hasn't been permitted to work with its Chinese counterparts since 2011, when Congress passed the Wolf Amendment citing concerns about espionage.
