Lunar Water Reserves Could Limit Moon Cities to Small Towns

The moon likely does not hold enough water to support the massive cities that major space leaders have promised to build within the next two decades. A recent analysis published in Frontiers in Space Technologies suggests that while power generation is not a major hurdle, water availability is the primary constraint for long-term human habitation on the lunar surface.

High-profile figures in the tech industry have recently shifted their public focus toward lunar settlement. In February, Elon Musk stated that SpaceX is prioritizing a self-growing city on the moon over Mars, potentially achievable in under ten years. Jeff Bezos has also predicted that millions of people will live in space by 2045. These bold claims prompted Martin Elvis, a senior astrophysicist at Harvard University, and Jonathan McDowell, an honorary professor at Durham University, to examine the underlying physics and resource limits.

The researchers determined that generating sufficient energy for one million people is a solvable problem using solar and nuclear sources. However, the water situation presents a much steeper challenge. Most of the moon's water is located in permanently shadowed regions at the poles. The study estimates that the moon contains roughly one billion tonnes of water, a figure that aligns with current scientific consensus.

Under these assumptions, a population of one million could survive for only about 100 years. This estimate relies on recycling 98 percent of all water used, a rate currently achieved on the International Space Station. Elvis noted that while a billion tonnes sounds vast, it is relatively small in practical terms. He compared the total volume to an aquarium the size of Central Park filled until the Statue of Liberty was just underwater, describing it as a small lake that cannot supply a big city for long.

Smaller settlements are more viable under these conditions. A town of 10,000 people could be sustainable for centuries if the same water assumptions hold true. McDowell emphasized that covering the moon with large cities, as depicted in science fiction, requires finding a way to transport water there because it is not currently available in sufficient quantities in one place.

The estimates used in the study may actually be generous. Elvis suggested that the one billion tonne figure could be 20 or 30 times too large. He further noted that only one-third to one-half of the available water would likely be recoverable. His best guess is that the usable amount is about one percent of the original figure, which would reduce the lifespan of a one million person city from 100 years to just one year.

There are also uncertainties regarding the physical form of the water. Gordon Osinski, a professor of planetary geology at Western University, pointed out that satellite measurements have limitations. He believes the water exists but needs ground confirmation. He suggested it might resemble Arctic permafrost, consisting of sub-millimetre ice crystals mixed into soil, which would be difficult to extract.

Despite these constraints, the researchers do not believe the findings are discouraging. McDowell argued that the truth is never negative. He stated that what is negative is trying to do something that is not going to work. The study suggests that while mega-cities are currently out of reach, smaller, sustainable communities remain a realistic goal for the coming decades.