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New infrared observations of the disks of dust and rock around young stars reveal that many planets apparently form in an environment more violent and chaotic over a longer period of time than previously theorized, astronomers reported yesterday.

The observations by NASA's Spitzer Space Telescope, combined with previous data from European satellites, showed that the dust clouds in these protoplanetary disks did not, as generally assumed, steadily fade away over a few million to a few tens of millions of years. Instead, the disks were frequently replenished by dusty debris from repeated collisions of large rocky objects. This chaos of creation sometimes persisted for hundreds of millions of years.

Scientists said the findings provided clues to how Earth-like planets are made and why they may be fairly common around other stars.


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