In 2015 Congress passed a law to legalise mining in outer space—the first of its kind in the world.

Firms that some day manage to mine asteroids for resources like water or precious metals would henceforth be allowed to own, process, and sell anything harvested. The nascent space-mining industry was thrilled. The boss of a firm called Planetary Resources compared it to the Homestead Act of 1862—a law that gave up to 160 acres in the American West to any plucky settler willing to venture forth.

More recently Wilbur Ross, the commerce secretary, has talked about creating a more “permissive” regulatory environment in space and turning the moon into a “gas station” for further exploration. Other countries are following suit: Luxembourg passed a similar measure last year and earmarked €200m to invest in space-mining companies.

But not everyone is pleased. At the UN committee dealing with outer space, Russia condemned the American move, citing America’s “total disrespect” for international law. Critics say America is conferring rights that it has no authority to confer. There are indeed legal grey areas.

Who owns what in outer space?