Earth is the only planet traveling within its nearly circular orbit around the sun. But what if Earth shared its orbit with another planet?
One of the most unusual ways in which two planets might “co-orbit,” or share the same zone around their star, are so-called horseshoe orbits. Instead of both worlds moving in a circle around a star, each would move along the edge of their own somewhat horseshoe-shaped track, with these crescents facing each other like two halves of a broken ring.
“I think horseshoe orbits are among the most exciting configurations for other Earths,” astrophysicist Sean Raymond at the Laboratoire d’Astrophysique de Bordeaux in France, told Live Science. “Since the two planets formed in the same disk around the same star, and likely from similar stuff, studying their evolution is akin to studying the lives of twins separated at birth.”