The flags of two countries hang unfurled — not by any breeze but by metal wiring — over the desolate, eerily still surface of the moon. One is the stars and stripes of the United States; the other, the crimson of China. But if you ask any official from these countries, they will tell you that these flags do not represent a property claim of any kind. They're more like extraterrestrial graffiti. 

But if planting a flag on the moon doesn't count as a property claim, then what does? And when you get down to it, can anyone actually own the moon? 

When the Soviet Union's Sputnik 1, the world's first artificial satellite, streaked across the sky in October 1957, it opened up a whole new realm of possibilities. Some of those possibilities were scientific, but others were legal. Over the following decade, the international community drafted the Outer Space Treaty(opens in new tab) of 1967 (OST), the world's first legal document explicitly pertaining to space exploration. 

This treaty remains the most influential piece of space law, despite the fact that it's very difficult to enforce. "It's not a code of conduct," said Michelle Hanlon, a space law expert at the University of Mississippi School of Law. "It's just guidelines and principles."

Despite the lack of enforceability, the OST is clear about countries making land grabs in space. Article 2 of the treaty explicitly rules out the possibility of a country claiming ownership of parts of space or any celestial bodies. "A state cannot claim sovereignty on the moon, period," Hanlon told Live Science.