Ever since their discovery, scientists have speculated on the mystery of Saturn’s rings. But Robin Canup, an astronomer with Boulder’s Southwest Research Institute, claims he’s solved the puzzle: The rings are the remnants of one of Saturn’s moons, which plunged into the planet some 4.5 billion years ago (via The Associated Press). As the moon spiraled into Saturn, gravity from the giant gas planet ripped ice from the moon, forming the rings, according to Canup’s article, to be published in the journal Nature. If true, the ice rings would have at one time been about 1,000 times more massive than they are today, Discovery News adds.

Canup’s theory is just one of many that attempt to explain the origins of Saturn’s rings, which likely helped form the planet’s inner moons. Other theories speculate that the rings are the remains of a moon hit by a meteor or that they’re the leftovers of a long-gone comet. Check out some recent photos of Saturn from NASA here.