LOS ANGELES - The Spitzer telescope's examination of hundreds of stars has found evidence that the times it takes to form an Earth-sized planet may last hundreds instead of tens of millions of years. The telescope revealed dust rings around nearby stars that couldn't have survived long unless violent collisions between gigantic chunks of rock were replenishing them, scientists said during a press conference Monday at NASA's Jet Propulsion Laboratory in Pasadena. Scientists have long believed that planets are formed when the dust in a disc-like formation around a young star begins to clump. Some of the clumps eventually grow...