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Craters on the moon could hold over a trillion dollars’ worth of platinum and other precious metals deposited there by asteroids. That means lunar prospecting may be more economically viable than travelling to asteroids individually to mine them – but the legality of doing this on the moon remains unclear.

, an independent researcher in Vancouver, Canada, and his colleagues looked at whether there may be commercial quantities of platinum group metals (platinum, palladium, rhodium, ruthenium, iridium and osmium) that were left behind by asteroids hitting the lunar surface.

“Today, astronomy is done to satiate our curiosity,” he says. “It has very few practical applications and is mostly paid for by taxpayer money, meaning that research funding is at the mercy of governmental policy. If we can monetise space resources — be it on the moon or on asteroids — private enterprises will invest in the exploration of the solar system.”

The team modelled the fraction of lunar craters thought to have been created by metallic asteroids, the number of these asteroids that had a sufficient concentration of platinum group metals, and how many would have crashed on the moon with a velocity small enough to leave significant remnants behind. They found that out of around 1.3 million craters on the moon with a diameter greater than a kilometre, nearly 6500 were made by asteroids containing commercial quantities of platinum.

This means there are potentially “a lot more craters on the moon with ore-bearing asteroidal remnants than there are accessible ore-bearing asteroids”, says Chennamangalam. At a rough estimate, he thinks there could be $1 trillion worth of platinum and other metals available for mining in lunar craters.

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Mining the moon would be easier than asteroids, he says, because most asteroids are further away than the moon, and their negligible gravity would make operations technically difficult. The moon’s gravity is only a sixth of that on Earth, but this would still make things easier.

However, even if lunar mining is technically easier, it may be legally more difficult. The Outer Space Treaty 1967 remains the cornerstone of international space law, setting the rules for all activities beyond Earth – including space resource mining. It states that “outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means” – but it is disputed whether asteroids are “celestial bodies” or private mining is “national appropriation”.

“While [the treaty] clearly applies to such activities, it leaves key questions unanswered,” says at the University of Sydney, Australia. “This includes clarity on the rules and governance for ownership of extracted resources, commercial licensing rights, equitable benefits sharing, environment protection standards to avoid harm and regulations for long-term occupation and permanent infrastructure on the moon.”

Some people have compared asteroid mining to international fishing, which is permitted even though no one owns the high sea, but it would be harder to make the same argument for mining the moon.

The US has recently attempted to clarify matters with a non-binding framework, known as the Artemis Accords, that establishes a set of principles governing the exploration and utilisation of outer space, particularly the moon, which would allow commercial exploitation. It has been signed by 55 countries, but not China or Russia, two major space powers, meaning there is still a lot of uncertainty.

“As private space mining and exploration activities loom near, it’s critical that we bridge the gaps in the Outer Space Treaty to ensure clear, fair rules for resource activities at the multilateral level,” says Connolly.