Science For All Newsletter: Cities on the moon may run dry far faster than space barons think

As NASA and China speed up their lunar space programmes, a more-than-temporary human settlement on the moon inches closer to reality. Space agencies with these plans are targeting the moon’s south pole region, where permanently shadowed craters are supposed to hold large quantities of water ice, which a human base can use as a water source.

In the long-term, entrepreneurs like Jeff Bezos have argued for moving heavy industries to the moon while Elon Musk said the satellite can even support a “self-growing city”. As on the earth, water is at the centre of all these plans.

But a new study by two astronomers, Martin Elvis of the Smithsonian Astrophysical Observatory and Jonathan McDowell of Durham University, has thrown up a reality check. The duo has estimated that even if the moon hosted one billion tonnes of water, it would support a population of only one million people for roughly a century if they recycled 98% of it.

The findings were published in Frontiers in Space Technologies.

The scientists arrived at this estimate based on calculations of how much water the moon may really hold, how much electricity people and industrial activities consume, how much water a human settlement might need, and how efficiently that water can be reused.

Right now, the exact quantity of water on the moon is a major source of uncertainty, and which scientists on the ground are studying using robotic missions like India’s Chandrayaan and China’s Chang’e programmes. One 2022 study of 65 large permanently shadowed craters estimated that eight of them together hold around 34 million tonnes of water. Research is however slowed, necessarily, by differences in instruments and different studies making different assumptions about the moon.

Against this backdrop, Elvis and McDowell assumed 1 billion tonnes of water as a generous baseline — around 4 lakh Olympic-sized swimming pools — and the demand to amount to 500 tonnes per person per year.

(The duo also estimated that a city of one million inhabitants would require around 2 GW of power, which can be sourced relatively easily from solar panels and nuclear reactors.)

Without recycling, this will sustain a million people for only around two years. But with 98% recycling, they estimated that a million people will deplete a billion tonnes of water in a century, and a lakh people in a millennium.

They also found one million people could have water for a millennium if they recycled the water to the tune of 99.75% — essentially living like the fictitious Fremen tribe in the ‘Dune’ books and films.

At present, NASA has said it will set up a permanent outpost near the moon’s south pole from the 2030s under its ‘Moon Base’ programme. China’s ‘International Lunar Research Station’ plans for a basic station by 2035 that will be built out in the 2040s.

India itself is planning a crewed landing on the moon by 2040. In August, NASA also invited the Indian Space Research Organisation to participate in the ‘Moon Base’.

Since Elvis and McDowell assumed a minimum population of one lakh for their analysis, the findings don’t apply to short-duration missions or small lunar outputs. But as these outposts expand, the study suggests, the space agencies and the governments behind them may have to treat water on the moon as a strategic resource.