Lunar water reserves support towns, not mega-cities

Commercial space leaders have outlined ambitious plans for large-scale lunar settlements, yet a new analysis suggests physical limits on available water may constrain those ambitions. The findings, published in the journal Frontiers in Space Technologies, examine whether the moon can sustain the population densities proposed by major industry 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, tested claims made by executives regarding lunar colonization. Elon Musk stated in February that SpaceX shifted its focus to building a self-growing city on the moon, a project he estimated would take under 10 years. Jeff Bezos of Blue Origin has separately predicted that millions of people will live in space by 2045.

The researchers determined that generating power for a million people is feasible using solar and nuclear sources. The constraint lies in water supply. Most lunar water is located in permanently shadowed regions at the poles. Assuming a total of one billion tonnes of water, the study found that a population of one million could survive for approximately 100 years. This projection assumes a water recycling rate of 98 per cent, a standard currently maintained on the International Space Station.

Elvis noted that while one billion tonnes appears substantial, it is relatively small. He compared the volume to an aquarium the size of Central Park filled until the Statue of Liberty was submerged. He described the reserve as a small lake, noting that such a quantity cannot supply a large city for an extended period. A settlement of 10,000 people, however, would be sustainable for centuries under the same conditions.

The study's baseline assumptions may be optimistic. Elvis suggested the total water estimate is likely 20 to 30 times too high. He further estimated that only one-third to one-half of the existing water is recoverable. His best calculation indicates that usable water may be as low as one per cent of the original figure, which would reduce the sustainability window for a million people from 100 years to one year.

Gordon Osinski, a professor of planetary geology at Western University in London, Ontario, noted that satellite measurements contain uncertainties. He suggested the water may exist in a form similar to Arctic permafrost, consisting of sub-millimetre ice crystals mixed into soil, which makes extraction difficult. McDowell stated that the findings provide a factual baseline for planning. He argued that understanding the limits allows engineers to design systems that work within the available resources.

The authors concluded that covering the moon with cities requires finding methods to transport water to the surface, as it is not currently distributed in accessible quantities. The research provides specific parameters for the power and water infrastructure needed to support various population scales on the lunar surface.