Lunar Cities May Run Dry Quickly

Major tech leaders have recently pitched the moon as the next great frontier for human habitation, yet a fresh scientific analysis casts doubt on the long-term feasibility of such plans. The study highlights a critical resource constraint that could limit the size and duration of future lunar communities.

SpaceX chief Elon Musk stated in February that the company is pivoting away from Mars colonization to focus on constructing a self-growing city on the moon. He projected this goal could be achieved in under a decade, a timeline significantly shorter than the more than 20 years estimated for Mars. Blue Origin head Jeff Bezos has also promoted a vision of millions of people living in space by 2045. These bold assertions prompted two scientists to examine the underlying logistics.

Martin Elvis, a senior astrophysicist at Harvard University's Smithsonian Astrophysical Observatory, collaborated with Jonathan McDowell, an honorary professor at the Durham University Space Research Centre in England. They published their findings in the journal Frontiers in Space Technologies. Their analysis focused on two fundamental requirements for survival: power and water. The results suggest that while energy generation is manageable, water availability poses a significant challenge.

The team determined that power needs are relatively straightforward to meet. Solar and nuclear sources appear sufficient to support a population of one million on the lunar surface. However, the water situation is far less optimistic. Most lunar water is believed to reside in permanently shadowed polar regions where sunlight does not penetrate. Based on current estimates of roughly one billion tonnes of available water, a million-person settlement could survive for only about 100 years. This calculation assumes a water recycling rate of 98 percent, matching the efficiency currently achieved on the International Space Station.

Elvis noted that while one billion tonnes sounds substantial, the volume is modest in a global context. He compared the amount to an aquarium the size of Central Park filled until the Statue of Liberty is just underwater. He described it as a small lake, noting that such a volume cannot supply a large city for an extended period. A smaller settlement of 10,000 people, however, would remain sustainable for centuries under the same assumptions. McDowell added that if humanity aims to cover the moon with cities as depicted in science fiction, new methods to transport water to the surface are necessary because it is not currently available there.

The researchers acknowledged that their assumptions might be generous. Elvis suggested that the one-billion-tonne figure is likely 20 or 30 times too large. He estimated that only one-third to one-half of the existing water would be recoverable. His best guess is that the usable amount is about one percent of the original figure. If this holds true, the lifespan of a million-person city would shrink from 100 years to just one year.

Physical extraction presents another layer of complexity. Gordon Osinski, a professor of planetary geology at Western University in London, Ontario, pointed out uncertainties in satellite measurements. He confirmed that the water likely exists but emphasized the need for on-ground verification. Osinski suggested the water may resemble Arctic permafrost, consisting of sub-millimetre ice crystals mixed into soil that are difficult to extract.

Despite these constraints, the scientists do not view the findings as a reason for pessimism. McDowell argued that the truth is never negative. He stated that what is negative is attempting projects that are destined to fail. The study serves as a reality check for the industry, urging planners to account for the hard limits of lunar resources before committing to massive urban development projects on the moon's surface.