A fragment from the same family of asteroids is thought to have wiped out the dinosaurs 65 million years ago.

据认为，同一小行星家族的一个碎片曾经在六千五百万年前灭绝了恐龙。

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NASA estimates there are 19 500 asteroids at least 330 feet wide - large enough to detect with telescopes - within 28 million miles of Earth.

这些物体是大量存在的，据NASA估计，仅地球28 000 000英里范围内超过330英尺宽的小行星就达19 500个，使用望远镜就可以观测到。

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Astronomers think there are about half a million asteroids the size this one near Earth, NASA said, but less than one percent have been detected.

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Between 500, 000 to 1 million large asteroids near are near Earth and Mars.

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In 2014 it intends to launch, at a cost of a few million dollars, a set of small space telescopes whose purpose will be to seek out asteroids which are easy to get to and whose orbits return them to the vicinity of Earth often enough for the accumulated spoils of a mining operation to be downloaded at frequent intervals.

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