When the solar system formed, a disk of gas and dust orbited the young sun. Over the course of millions of years, the dust gradually clumped together to form kilometer-sized chunks known as planetesimals. Some grew into planets, while the rest are considered to be the precursors of today’s asteroids. Researchers assume that this development did not proceed in a linear fashion, with different stages of planetesimal development occurring simultaneously, and not every region of the disk offering favorable “starting conditions” for planetesimals.

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