'Rogue' asteroids often found where don't belong

"Rogue" asteroids -- space rocks with compositions at odds with their position in the solar system - may be the norm, not the exception, U.S. astronomers say. Many scientists had long believed the solar system's asteroid population was essentially static -- those that formed near the sun remained near the sun, while those that formed farther out stayed on the outskirts. But in the last decade, asteroids that appear to have formed in warmer environments -- that is, closer to the sun -- have been found further out in the solar system, and vice versa, researchers at the Massachusetts Institute of Technology, working with colleagues at the Paris Observatory, reported Wednesday. The scientists analyzed the size, composition and location of more than 100,000 asteroids throughout the solar system and found rogue asteroids are more common than previously thought -- suggesting the early solar system may have undergone dramatic changes before the planets assumed their current alignment. Jupiter may have drifted closer to the sun, they suggest, dragging with it a host of asteroids that originally formed in the colder edges of the solar system, before moving back out to its current position, simultaneously disturbing more close-in asteroids, scattering them outward. "It's like Jupiter bowled a strike through the asteroid belt," MIT researcher Francesca DeMeo said. "Everything that was there moves, so you have this melting pot of material coming from all over the solar system." The findings could help scientists refine theories of how the solar system evolved early in its history, he said.