Science fiction has long given us depictions of humans living on the Moon. In recent years, as technological advances have continued at pace, space entrepreneurs have started making plans for how they could actually do it.
However, a new study published this week by the Harvard–Smithsonian Center for Astrophysics (CfA) has provided a reality check, finding that the biggest obstacle facing would-be colonisers are the Moon’s existing ice reserves, which are insufficient to support a lunar city.
The study, titled "There Are No Cities on the Moon," looked at how much power and water a large population would use on the Moon, how long a city of 100,000 or one million people could survive there, and how sustainable maintaining a lunar city would be.
Its findings were published in the international journal Frontiers in Space Technology.
The study comes after several lunar exploration missions and analyses earlier this year that have more accurately mapped the lunar surface, as well as where and how much water is present, prompting renewed speculation over humanity’s capacity to set up shop there.
Scientists have long known about the presence of water deposits on the Moon, with the most recent analyses confirming that the reserves are held in shadowed craters — deep depressions that never see sunlight.
With temperatures hovering between minus 163 and minus 246 degrees Celsius, only around a millimetre of ice is lost every billion years.
Martin Elvis, a senior astrophysicist at the CfA who led the study, said that in their research, a “city” was defined as a settlement with a population of one million people, with average water use per person estimated at 500 tonnes.
Given these figures, a city of this size would run dry in just a few years unless it turned to recycling — but this would not entirely solve the issue either.
The International Space Station (ISS) currently recycles about 98% of its water.
According to Elvis’s calculations, if one billion tonnes of lunar water were reused with the same efficiency as on the ISS, a lunar city with a population of one million could be sustained for around 100 years.
For a Moon city to last beyond this, its population would likely need to be capped at around 1,000 people. So, less moon city and more moon village.
However, if the Moon city could recycle 99.9% of its water, its one-million-strong population could, in theory, survive stably for about 2,000 years. This could be supported by other water-efficiency measures, such as vertical farming, or alternatively by importing water.
Energy, though, would not be an issue for a lunar city, which could be powered by abundant solar energy. Around the lunar poles are so-called High Illumination Regions, where the Sun never fully sets, instead remaining on the horizon.
The rims of craters in these regions sit higher than the surrounding terrain, making them an ideal location for photovoltaic installations that could harness solar energy constantly.
According to the study, 1 kilometre-tall towers covered with solar panels on crater rims could each generate about 3 gigawatts of power — enough to power not only residential facilities but industry too.
Not only that, but one of the main raw materials for solar cells, silicon, makes up 20% of the Moon’s surface, meaning manufacturing could be localised to some degree — something some companies are planning to take advantage of.
Japanese construction firm Shimizu Corporation announced plans earlier this year to install solar panels along the lunar equator to generate 13,000 terawatts of power — more than the entire electricity consumption of Earth.
The Moon’s thin atmosphere means solar power generation is unaffected by weather, offering the advantage of a consistent energy output.
So, while a lunar city of one million people might not yet be possible, serious colonisation might not be far away.
And even though current exploration technology can only examine up to a few metres below the surface, more significant ice reserves could be found deeper beneath the surface in the future.
Commenting on the study, Martin Elvis said he hoped “this paper will serve as a catalyst for all stakeholders involved in lunar exploration to seriously discuss the overall sustainability of the Moon, particularly long-term water resource management”.
