Scientists say moon lacks enough water to sustain large cities

SpaceX founder Elon Musk recently declared a shift in focus toward building a self-sustaining city on the moon within a decade, but a new scientific study suggests a major obstacle. Research published in the journal Frontiers in Space Technologies concludes the moon lacks sufficient water to support a large, permanent human civilization. The analysis by astrophysicists Martin Elvis of Harvard University's Smithsonian Astrophysical Observatory and Jonathan McDowell of Durham University examined the resources needed for a lunar settlement. They found that while solar and nuclear power could meet energy needs for a million people, the water supply is the limiting factor.

Current estimates suggest roughly one billion tonnes of water exists on the moon, primarily in permanently shadowed regions at the poles. The researchers calculated that a population of one million people, recycling 98 per cent of their water as done on the International Space Station, would exhaust that supply in about 100 years. "Our work shows that, yeah, if you want to have an Antarctic base on the moon for the next few hundred years, no problem. If you want to have a small town, that's doable," McDowell said. "If you want to cover the face of the moon with cities, like in the best science fiction, then you have to find a way to get the water there, because it's not there right now."

Elvis noted that one billion tonnes of water, while sounding vast, is equivalent to a small lake. "If you had a huge aquarium the size of Central Park in Manhattan, you could fill it up to where the Statue of Liberty was just underwater and that's the amount of water you've got," he said. "So it's huge in one way, but … it's a small lake. And a small lake is not going to supply a big city for very long." The study found a much smaller settlement of 10,000 people could be sustainable for centuries under the same assumptions.

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However, the scientists caution that the one-billion-tonne estimate is likely far too optimistic. Elvis said the real amount of accessible water is probably 20 or 30 times smaller. He also doubts we could recover all the water present, estimating only one-third to half might be extractable. "So my best guess is the real amount of water available that we can be fairly confident about is one per cent of what we said before," Elvis explained. "So instead of 100 years, it's one year."

Beyond quantity, the form of the lunar water remains a critical unknown. Gordon Osinski, a professor in planetary geology at Western University, said satellite detections need ground confirmation. "I think it is there, but let's go and ground-truth that and confirm it," Osinski said. "And then there's the bigger unknowns of what form it's in…. Is it more like the permafrost up in the Arctic, where it's basically soil with, you know, sub-millimetre size ice crystals, which are hard to get out of?"

McDowell said the findings are not meant to dampen exploration but to provide realistic parameters. "The truth is never negative," he said. "What's negative is to actually go and try and do something that isn't going to work." The research comes as Musk posted on social media in February that SpaceX had shifted focus to a lunar city, which he said could be achieved in less than 10 years compared to more than 20 for Mars. Blue Origin CEO Jeff Bezos has also predicted millions of people living in space by 2045.

With files from CBC News