The origin of the moon月亮起源说

迟琳

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Since the dawn of human history， themoon has influenced religion and poetry.But as the moon appears in the sky， wewonder，“What is the origin of the moon？”Before the invention of the lunarprobes （月球探测器）， scientists had pro?posed three theories. The first declared themoon was a fragment （碎片） produced froman early earth that rapidly turned. The sec?ond origin theory assumed that the moonand the earth formed side by side from thecooling down of original gases and par?ticles. The third theory said the earth andthe moon originated at widely separatepoints in the solar system， but as they gotclose， the moon was pulled into orbitaround the earth.

But in 1975， after studying moonrocks and close?up photographs of the lu?nar surface， scientists proposed another，more probable theory—“planetesimal im?pact”. According to this theory， a veryhuge object known as a planetesimalstruck the earth more than 4 billion yearsago. At first， scientists estimated the ob?ject was about the size of the planet Mars.

But in 1997， a US computer simulationshowed it must have been at least two?and?a ? half to three times Martian size. Thetheory is that the destructive impact forcedparts of the earth and this giant object intospace， where the fragments eventuallycame together to create the moon.

By the 1990s， this theory had becomethe most widely accepted explanation ofthe moons origin. But it still poses a majorproblem： Where on the earths surface isthe crater （坑） created by the planetesimalsimpact？

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