Cities won’t survive on the moon as there isn’t enough water, scientists say

“For such a large investment, a lifetime of about a century seems to fall short of the sustainable, long-term settlement beyond Earth that some advocate,” the researchers noted.

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(CNN) — If, like Elon Musk, you have been dreaming of a future in which large populations of humans can live on the moon, you’re likely to be disappointed.

Even though there could be trillions of pounds of water trapped inside tiny glass beads spread across the lunar surface, scientists estimate that this won’t be enough to sustain a big city for very long, according to a study published Monday in the journal Frontiers in Space Technologies.

Musk announced in February that his aerospace company, SpaceX, had shifted its focus from developing a settlement on Mars to “building a self-growing city on the Moon,” because it would be quicker to achieve, potentially “in less than 10 years.”

That raised the question, “Well, how big a city could you support on the moon with that water supply? And the answer was very surprising,” lead study author Martin Elvis, a senior astrophysicist at the Harvard and Smithsonian Center for Astrophysics, told CNN.

Taking 1 billion tons of water as a “generous” estimate, Elvis and his colleague, astrophysicist Jonathan McDowell, who is now an honorary professor at the UK’s Durham University Space Research Centre (SPARC), calculated how long populations of various sizes could last if they were using water for drinking, hygiene, growing food, rocket fuel and even breathing.

They found that a population of 1 million people — about the number of people who live in Sweden’s capital, Stockholm — would finish the water supply in under two and a half years, according to the study.

However, if the water was efficiently recycled, such as at the 98% water recovery rate that the International Space Station has achieved, it would take a city of 1 million people 100 years to deplete it. And “that depends on people being very nice” about their water usage, Elvis said, including “always using rather dubious toilets and not doing laundry,” and this behavior is “unlikely to be sustainable, I would think.”

“For such a large investment, a lifetime of about a century seems to fall short of the sustainable, long-term settlement beyond Earth that some advocate,” the researchers noted.

They calculated that a small city of about 100,000 people — slightly fewer than the number of people living in Sandy Springs, Georgia — could survive for 1,000 years, which “seems long enough to justify being called sustainable.”

“If you have a small town of only 10,000 people… then you’ve got… 10,000 years’ worth of water, and that starts feeling like, okay, on a 10,000-year timescale, we can find another solution,” McDowell told CNN.

For example, there is “a lot of water in the solar system,” including water in the asteroid belt and on the moons of Saturn, he said. So, maybe in the future, those on the moon could import “deliveries of water in the quantities required to sustain a large population. It’s hard to see practically how to do that with current technology, but in the long term, maybe you can do that.”

In the short term, he suggested that instead of a city on the moon in 10 years, as Musk proposed, “I would say within 30 years we might have a town on the moon. That would be the way that I would translate what Elon said.”

‘Moon village’

“This is an important study. I think the authors have done a valuable service by injecting some realism into the discussion of longer-term plans for establishing large human settlements on the Moon,” astronomer Ian Crawford, a professor of planetary science and astrobiology at Birkbeck, University of London, who was not involved in the research, told CNN.

“If such settlements are to become established, I think the authors are correct in pointing out that water (or at least hydrogen to manufacture water from oxygen in lunar rocks) will need to be imported,” Crawford added over email.

A “Moon Village” of 1,000 inhabitants — about the amount of people who stay in Antarctica during the winter — could be “relatively carefree in our use of lunar water,” the researchers noted in the study. Crawford said in the short term, there is probably enough water at the lunar poles to support small-scale research outposts of this size, “and I think this will be the most likely use in the coming decades.”

However, he added that it is “also important to note that the water ice at the lunar poles is of great scientific interest, and we need to be able to study it properly before it is all dug up for water.”

The ice on the moon has accumulated over billions of years since its formation and “therefore preserves a chemical and physical record of the environment in which our Earth has existed for all this time, and which led to the development of life on Earth,” Simeon Barber, a senior research fellow at the UK’s Open University who looks for water on the moon, told CNN over email.

“We should at the very least work out secrets this ice holds for our own evolution and that of our planet — and of other planets — before we consider extracting it for industrial use,” Barber, who was not involved in the study, added.

Need to prevent ‘gold rush’

Agriculture puts the most demand on water resources, with the study using the World Bank’s estimate that feeding one person for one day requires two to five tons of water, or 2,000 to 5,000 liters. Ways of cutting water usage could include adopting a vegan diet, as the water needed to produce beef is six times that of soybeans, and chicken needs double, according to the study.

However, even if people optimize their usage of water, there is still “huge uncertainty in how much water there actually is on the moon,” McDowell said. “But also, how easy is it going to be to extract?”

McDowell, who said “water is going to be the gold of the solar system,” added that there is some suggestion that in the very cold, shadowed craters, the water content could be quite high, “which would make it relatively easy to extract. But on a lot of the area of the South Pole, there might be water in trace amounts among the rock and that, even if it adds up to a lot, it would be super hard to actually get out of the rock.”

Barber said the “extreme cold and extensive darkness” in those regions make them an “inhospitable place for robotic or human workers. The water is not in the form of pristine sparkly ice cubes that we could melt and drink; it is likely laced with a cocktail of poisonous chemicals that first must be removed.”

The eight biggest craters on the moonare estimated to contain about 34 million tons of water, according to the researchers. With so few big craters to explore, interested parties might “try to grab the biggest and best of them and exploit the water,” said Elvis, who urged those involved in the space race to work with — not against — each other.

The researchers “are surely correct that careful management of the limited reserves of lunar water will be required,” Crawford said. “In turn, this implies the need for an internationally agreed regulatory framework, to prevent a ‘goldrush’ mentality developing which could prematurely deplete a valuable lunar resource.”

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