Astronomers Fathi Namouni of the Côte d’Azur Observatory in Nice, France, and Helena Morais of Universidade Estadual Paulista in Rio Claro, Brazil, used computer simulations to show that the asteroid, which shares its orbit with Jupiter, could have been traveling in reverse ever since the solar system’s youth. Because asteroids in the infant solar system formed from one swirling cloud, they should have all been traveling in the same direction. So the best explanation, the duo suggests, is that the rock, known as 2015 BZ509, migrated here from another star’s planetary system.
“It’s certainly an interesting possibility,” says astronomer Martin Connors of Athabasca University in Canada. But, he says, the study doesn’t nail down whether the asteroid actually came from outside the solar system.
Such asteroids are faint and hard to get information from, Connors says. “There isn’t really a blazing sign saying, ‘Hey, I’m not from here.’ ”