In the case of a planet, the hole is carved out by an asteroid or comet impact.

对于行星，这个洞就是由小行星或彗星碰撞打开的。

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Since the era of industrialization, Fenner said, humans have had an effect on the planet rivaling any ice age or comet impact.

Fenner说，自从工业化时代以来，人类活动对地球产生作用，其影响堪比冰河时代或彗星的破坏作用。

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And when an asteroid takes a nosedive into a gas giant's atmosphere, it leaves different thermal and chemical fingerprints to a comet impact.

当一颗小行星进入一个气体天体的大气层时，会留下不同的热度和化学影响。

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The asteroid or comet impact widely implicated in the dinosaurs' demise would also have damaged plankton production in the oceans.

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What about an asteroid or comet impact?

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Deep Impact has now set its sights on comet Ison during a 36-hour period in mid-January.

BBC: Comet Ison caught on film by Deep Impact craft