Earth has a new follower: Asteroid 2010 SO16, which has joined the Earth's path around the sun and could follow it for the next 120,000 to 1 million years, scientists say. But there's one odd thing about the asteroid, which just so happens to be the largest space rock discovered so close to Earth: It orbits the sun in a horseshoe pattern.
When the asteroid entered the sun's orbit, it was further away than Earth and thus orbited slower. But as Earth caught up, its gravitational pull eventually drew SO16 closer to the sun, thus speeding up the asteroid's orbit. But as the asteroid, now faster than Earth, caught up again, this time Earth's gravitational pull moved it away from the sun—and the cycle began again, and will continue until the asteroid dies. The Daily Mail has an illustration. (Read more Earth stories.)