Harvard Researchers Say Lunar Water Reserves Cannot Support Million-Person Moon Cities

Lunar water supplies fall far short of supporting the million-person settlements proposed by space industry executives, according to a new analysis by two researchers who tested those plans against available power and water figures.

Martin Elvis, a senior astrophysicist at Harvard University's Smithsonian Astrophysical Observatory, and Jonathan McDowell, an honorary professor at the Durham University Space Research Centre, published their paper in Frontiers in Space Technologies. Their work examines claims made this year by SpaceX CEO Elon Musk, who wrote on social media in February that the company had shifted its focus from settling Mars to building a "self-growing city on the moon" achievable in under 10 years, and Blue Origin CEO Jeff Bezos, who has said "millions of people" will live in space by 2045.

Power presents no barrier to that scale, the researchers found. Solar and nuclear sources could sustain one million people on the lunar surface. Water does not follow the same path. Most lunar water is believed to sit in permanently shadowed polar regions where sunlight never reaches. Assuming roughly one billion tonnes, in line with current estimates, a population of one million could last only about 100 years, and that figure depends on recycling 98 per cent of the water, the rate achieved on the International Space Station. Elvis compared the total to "a small lake" and said "a small lake is not going to supply a big city for very long." A town of 10,000 people would be sustainable for centuries under the same assumptions. "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," McDowell said.

The calculation rests on assumptions that Elvis called generous. He said a billion tonnes is probably "20 or 30 times too big" and that only one-third to one-half of the water present would likely be recoverable. His best estimate for water that can be counted on is about one per cent of that figure, which would shrink the 100-year projection to one year. Gordon Osinski, a professor of planetary geology at Western University in London, Ont., said satellite measurements carry uncertainties and that he wants the water confirmed on the ground. He said it could resemble Arctic permafrost, with sub-millimetre ice crystals mixed into soil that are hard to extract.

McDowell said the findings should not be read as discouraging. "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."

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