A city with one million inhabitants on the Moon would not be sustainable for more than a century, even in the most favorable scenario of water availability and recycling, according to a study published in the journal Frontiers in Space Technologies. The researchers estimate that a small lunar town could run out of water after as little as a decade.
The discovery of icy water in permanently shadowed craters near the Moon’s poles has fed plans to install permanent bases and, in the future, villages, towns, and even industrial units on Earth’s natural satellite. However, Martin Elvis and Jonathan McDowell analyzed whether the available resources would be sufficient to sustain human communities without continually relying on water transported from Earth.
The presence of water at the lunar poles is partly due to the extreme conditions within the craters. Some zones have not received direct sunlight for about four billion years and exhibit temperatures below 110 kelvin, about -163 °C. These “cold traps” allow water ice to be preserved for extremely long periods, despite the vacuum on the lunar surface.
Estimates based on several lunar missions point to the possibility of up to one billion tonnes of water existing in these regions. The discovery altered perspectives about permanent human presence on the Moon, since it would, in principle, allow producing food and using water for basic needs without transporting all resources from Earth.
Energy would not be the main problem
The researchers consider that energy production would be relatively easier to resolve. The elevated areas near permanently shadowed craters receive sunlight for much of the time, allowing the installation of large photovoltaic systems.
According to the analysis, towers about one kilometer tall equipped with solar panels could produce up to three gigawatts of electricity. The panels themselves could, in the future, be manufactured on the Moon, since silicon is abundant in the lunar regolith.
This availability of energy could even enable the installation of data centers for artificial intelligence near the regions of near-permanent illumination and contribute to the development of a lunar economy.
Water is the main obstacle
The problem arises when analyzing water consumption. Without recycling, even an initial reserve of one billion tonnes would be consumed by a large city in only a few years.
Even assuming a recycling rate of 98%, equivalent to that currently achieved on the International Space Station (ISS), a lunar city with one million inhabitants would exhaust the available water in just over a century.
And current estimates are far less optimistic regarding the amount of water actually present on the Moon. The best available calculations point to an amount roughly 30 times smaller than one billion tonnes. In that scenario, the period until water depletion would be reduced by the same proportion, which means that even a small city could run out of water after about a decade.
A community of one thousand inhabitants, or even a city of ten thousand, would have significantly more favorable prospects and could be sustainable for several centuries.
The researchers identify, however, several possibilities to increase the viability of a future lunar occupation: significantly improving water recycling efficiency, reducing consumption through techniques such as vertical farming, importing water from accessible asteroids, or discovering new water reserves on the Moon itself.
This latter possibility may be the most promising. Current prospecting techniques can study only a few meters below the surface, while the lunar regolith, a layer of rock and fragments that covers the satellite, can reach dozens of meters in depth and contain water in the permanently shadowed regions.
Thus, before turning the plans to build lunar cities into reality, the researchers consider that it will be necessary to know exactly how much water exists underground. For the ambitions of establishing permanent communities on the Moon, “finding more water will be the first step.”
