The story

A new study published in Frontiers in Space Technologies finds that the Moon's water reserves may be too limited to sustain large-scale, long-term human settlements. Researchers estimate there are around 1.3 trillion pounds, or 600 million metric tons, of water ice in permanently shadowed craters near the lunar poles. A city of over one million people would exhaust the estimated amount of water on the Moon in a little over two years, or about 2.4 years, without recycling.

Even with highly efficient recycling at 98 percent, similar to the International Space Station, a city of one million people could only sustain itself for about 100 years, according to the study by Dr. Martin Elvis of the Smithsonian Astrophysical Observatory and Dr. Jonathan McDowell. The researchers used an optimistic baseline of one billion metric tons of water, but note the actual amount could be 20 to 30 times less. A smaller city of about 100,000 could sustain itself for around 1,000 years with the same recycling standards.

The findings cast doubt on plans by Elon Musk to build a self-growing city on the Moon in less than 10 years. The study suggests a Moon village of roughly 1,000 to 10,000 people would be more realistic for long-term settlement. Possible solutions include more efficient water recycling, reduced water use through techniques like vertical farming, importing water from asteroids, or discovering more water deeper in the lunar surface. Power generation would be less of a problem, as solar panels could be placed on crater peaks that receive near-continuous sunlight.