Although previous studies have found hydrogen and oxygen in moon minerals – implying the presence of water – whole molecules of H2O have never been detected in lunar rock until now.
There really is water on the moon. Molecules of H2O have been detected in lunar rocks for the first time in samples picked up by China’s Chang’e 5 spacecraft. These minerals could provide a source of water for a moon base, as well as offer fresh clues about the moon’s history.
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| An image of the lunar surface taken by the panoramic camera aboard the Chang’e 5 spacecraft after landing on the moon China National Space Administration/CNS/AFP via Getty Images |
The moon was long thought to be bone dry, but in the past 20 years, we have seen signs of small amounts of water buried below the surface. In 2008, researchers claimed to have found water in volcanic glass beads in samples of lunar rock collected by the Apollo missions. However, that study and others since actually detected hydroxyl groups – oxygen and hydrogen bound together – rather than molecules of H2O. To get water out of these rocks, they would need to be heated to around 1000°C.
Satellites orbiting the moon have also detected signatures of light that imply the presence of water ice, but this hasn’t been directly measured in a sample.
Now, Xiaolong Chen at the Chinese Academy of Sciences in Beijing and his colleagues have analysed around 1000 micrometre-sized grains of lunar soil brought back by Chang’e 5. Using X-ray diffraction, they found a mineral consisting of around 40 per cent H2O, along with ammonia, magnesium and chlorine. “This is a new form of water stored on the moon,” says Chen.
Its chemical structure is remarkably similar to that of a mineral called novograblenovite that was discovered by geologists near a Russian volcano in 2019. This was formed from hot gases from a volcano passing near basalt rock, and a similar process may have created the lunar mineral too, says Chen. It also means we can infer that gases containing ammonia or chlorine may have been present in early lunar volcanoes, he says.
While the amount of the mineral in the lunar soil was tiny, it would be much easier to extract water from it compared with other potential sources of water on the moon, says Shifeng Jin, a team mmber at the Chinese Academy of Sciences. Because the new material the researchers have found contains full molecules of water, it only needs to be heated to around 100°C, says Jin. If the mineral can be found in significant quantities near an old lunar volcano, it could make a good source of water for future astronauts, he says.
The most widely accepted hypothesis for how the moon formed is that it is the product of a collision between Earth and another planet. When this happened, it should have lost most of its volatile material, like the oxygen needed for water, says Sara Russell at the Natural History Museum in London. Because of this, many scientists think the moon acquired most of its water from asteroid impacts.
But if more lunar soil is widely rich in volatiles like ammonia and chlorine, as the Chang’e 5 sample is, then it could imply that asteroids didn’t supply the moon’s water and that it instead came from within the moon when it was created. This would be a huge change to our understanding of lunar history, but we need more evidence to establish this, says Russell.
Journal reference:
Nature Astronomy DOI: 10.1038/s41550-024-02306-8