Three possible scenarios for the evolution of asteroid belts. Top: A Jupiter-size planet migrates through the belt, scattering material and inhibiting the formation of life on planets. Middle: A Jupiter-size planet moves slightly inward but is just outside the belt (this is the model proposed for our solar system). Bottom: A large planet does not migrate at all, creating a massive asteroid belt. Material from the hefty asteroid belt would bombard planets, possibly preventing life from evolving.
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