The inside of the moon is wetter than previously thought, research suggests, opening up fresh possibilities for manned missions to the lunar landscape.
While the moon was once thought to be bone-dry, in recent years water has been found trapped in lunar volcanic glasses – material formed from magma ejected from the moon’s interior.
But it has remained a topic of debate just how wet the lunar innards are, with some arguing that the water content of lunar samples may not be representative of the majority of the moon’s mantle – the layer beneath the crust.
Now researchers say a new analysis of satellite data has unpicked the puzzle, revealing “hotspots” of trapped water right across the moon’s surface in deposits from ancient eruptions.
“The lunar mantle is wetter than our previous thoughts [suggested],” said Shuai Li, co-author of the study from Brown University.
The finding, he adds, has important ramifications, not least for our understanding of how the moon formed – an event that occurred when a Mars-sized body collided with the Earth 4.5bn years ago – but also our understanding of the internal structure of the moon, and the mystery of its once-strong magnetic field.
The new findings, published in the journal Nature Geoscience, come from analysis of data captured by the Moon Mineralogy Mapper instrument on board the Chandrayaan-1 orbiter, an Indian lunar probe that launched in 2008.
While the data has been scrutinised before, signals from water trapped in materials on the lunar surface had previously been masked by thermal radiation emitted by the moon.
But a new computer model, based on data from samples brought back from the moon and checked against data relating to the temperature of the lunar surface, has allowed researchers to clear away the confusion and look just at levels of trapped water.
The team applied this model to a band of lunar surface that does not include the poles, where water ice is known to exist.
The results reveal that the majority of this band of the moon’s surface, including its highlands, plains and impact craters, has only background levels of trapped water – attributed to protons that have been “implanted” in the soil by solar wind striking the moon. But some regions show an excess – including areas near the Apollo 15 and Apollo 17 landing sites where samples of water-rich volcanic glasses had previously been collected.
These regions range from small areas to those reaching thousands of square kilometres and are thought to be deposits from ancient eruptions. “The beauty of these results is after you subtract the background, all the hotspots are associated with the pyroclastic deposits, no exceptions,” said Li.
The authors write that, for these large deposits, the excess water content is up to four times that of background levels, but Li added that variations in values between the deposits could be down to differences in the water content of the magma that formed them, or variations in materials that made up the magma which led to it cooling at different rates, resulting in different levels of water loss.
But the new research does not solve the debate about where the moon’s watercame from in the first place. “Whether it is from the Earth or from impact delivery … we are not ready to answer that question,” said Li.
Mahesh Anand, a planetary scientist at the Open University who was not involved in the study, welcomed the research, pointing out that such remote sensing was a “pretty damn good achievement.”
But, he noted, not all of the large pyroclastic deposits had an elevated water content. Li admits that is a puzzle, but pointed out that the majority of deposits examined were “wet”, suggesting dry deposits are an exception rather than the rule.
However, Anand agreed with Li that the findings could have wide-reaching implications, including for future plans for humankind to return to the lunar landscape.
“The first resource that people are going to look for when they go beyond Earth is water,” said Anand, pointing out the new study shows that the lunar poles are not the only possible destination. “You can land much more easily onto the equatorial region of the moon and if there is a nearby water deposit or possibility of extracting water then that becomes an attractive proposition as well,” he said.
Originally published on The Guardian
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