Rock Farm: Most asteroids lie in the main belt [white] between Mars and Jupiter and pose no threat.

太空岩石场：大部分小行星位于火星和木星之间的小行星带（图中白色部分），对地球没有威胁。

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It now appears when the asteroids and planets were first forming in the very early Solar System ice extended far into the Main Belt region.

现在看来，在太阳系初期行星和小行星首次形成时，冰深深地延伸进入主带区域。

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Critically, the Baptistina family of asteroids - those that were formed when the larger asteroid destructively entered the main belt - were only formed around 80 million years ago.

BBC: Asteroid thought to kill dinosaurs may not be guilty