There is water on the moon, and scientists have confirmed where it is stored in large quantities. The mineral in lunar dust collected by China’s Chang’e-5 lander and brought back to Earth was recently discovered to contain so much water that it makes up 41 percent of its weight. The mineral is similar to novograblenovite, discovered in basaltic rock on Russia’s Kamchatka Peninsula just a few years ago. Both the lunar and terrestrial versions have a chemical formula (NH4)MgCl3-6H2O and a similar crystal structure.

Given that we can study novograblenovit right here on Earth, the discovery of a nearly identical mineral on the Moon could give us some clues about where lunar water is stored and how it got there, as well as the history of lunar H2O.

The origin, existence and distribution of water on the Moon remains a mystery. That’s what scientists want to know because where the Moon’s moisture comes from and where it is now is an important part of the history of the Earth-Moon system. And since humans need water to survive, knowing where water is stored is important for future lunar exploration missions.

Water has been found in ancient lunar samples before, trapped inside tiny glass beads that form when surface material melts and forms globules. The detection of water signals in the spectrum of light reflected from the lunar surface suggests there’s much more out there.

One common idea is that water is associated with minerals that make up the lunar regolith, but previous research suggests that the hydrogen and oxygen bound in the lunar soil may be in the form of other hydroxyl molecules (compounds made up of hydrogen and oxygen in different ratios than water).

But when Chang’e-5 landed on the moon in December 2020, it made a breakthrough — the first in situ discovery of what appeared to be water in a moon rock. But it was unclear whether it was truly molecular water or another hydroxyl molecule. That required more comprehensive analysis than a robotic launcher could provide.

Now, humans on Earth, led by physicists Shifeng Jin and Munan Hao of the Chinese Academy of Sciences, have performed this analysis by subjecting samples sent back to Earth by the Chang’e-5 mission to X-ray crystal diffraction and chemical isotope analysis to determine whether the lunar regolith contains water or something else.

Their efforts revealed the existence of molecular water: a mineral (NH4)MgCl3-6H2O contains up to six water crystals.

Neograblenovite forms rarely on Earth as a result of the interaction of red-hot basalt with water and ammonia-rich volcanic gases. The lunar mineral is not exactly the same; its chlorine isotope has a different composition to that of Earth’s chlorine isotopes, but the mechanism of formation is probably quite similar. This suggests that a source of water and ammonia existed on the Moon in the past when there was active volcanic activity on the Moon.

“Thermodynamic analysis shows that the lower limit of the water content of lunar volcanic gas at that time was comparable to the water content of Lengai volcano, the driest volcano on Earth today,” the Chinese Academy of Sciences said in a statement. “This reveals the complex degassing history of a lunar volcano, which is of great significance for studying the evolution of the Moon.”

The discovery also points to a previously unknown source of water on the Moon: hydrated salts. They are much more stable than water ice, suggesting they could be found even in areas of the Moon frequently illuminated by sunlight, reducing our potential reliance on water ice hidden deep in shadowy craters at the lunar poles. The results of the research were published in the journal Nature Astronomy.