Astronomers group asteroids into different classes based on how the rocks reflect light in space.

天文学家通过在太空中反射光的方式将小行星分门别类。

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Earth has avoided such an event since in part because of Jupiter's gravitational field which limits our exposure to space rocks.

地球之所以避开了这样的危险，是因为木星引力场的作用，使得地球并不是完全“暴露”在太空岩石的危险之中。

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In their quest for water on our planet's satellite, researchers have had to rely on the analysis of lunar rocks that US Apollo space missions brought to Earth in the late 1960s and early 1970s.

在他们对于在我们这颗行星的卫星上是否有水的追求下，研究者们不得不依靠美国阿波罗太空任务带来将20世纪60年代末和70年代早期地球月球岩石带回地球进行分析。

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Amino acids have already been found in space rocks called meteorites.

VOA: special.2009.09.30

In proving that the earth takes a regular beating from space rocks he opened the way for others, in 1980, to find traces of the meteorite that killed the dinosaurs.

ECONOMIST: Gene Shoemaker

The meteor event in Russia on Friday is a sobering reminder that space is a busy place, and that space rocks can take us by surprise.

BBC: Science & Environment