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This is Scientific American's 60-second Science, I'm Christopher Intagliata.

这里是科学美国人——60秒科学系列，我是克里斯托弗·因塔格里塔。

On July 20th, 1969, humankind finally set foot on the surface of the moon. Fifty years later a big mystery remains¹: how the heck the moon got there in the first place.

1969年7月20日，人类终于踏上了月球表面。五十年后，一个巨大的谜团依旧存在：月球一开始到底是如何形成的？

For decades, the thinking has been that four and a half billion years ago a Mars-sized protoplanet smashed into the Earth. When the dust settled, our moon remained, forged from the debris² of Earth and the other object.

数十年来，人们一直认为是45亿年前一颗火星大小的原行星撞击了地球。尘埃落定后，月球留了下来，它是由地球和其他物体的碎片形成的。

Problem is, as scientists have taken more and more precise isotopic³ measurements of the Moon they've found that it's nearly identical in composition to the Earth—not some other object.

问题是，随着科学家对月球进行了越来越精确的同位素测量，他们发现月球的构成与地球——而不是其他物体——几乎相同。

"A problem I've been advertising⁴ as an isotopic crisis." Jay Melosh studies planetary impacts at Purdue University. Now, he says, a new theory in the journal Nature Geoscience may at least point to a way out of that isotopic crisis of the moon's chemical isotopes⁵ so closely resembling Earth's.

“我一直在宣传的一个问题是同位素危机。”在普渡大学研究行星撞击的杰伊·梅洛什说到。现在，他说，《自然·地球科学》期刊上发表的一项新理论可能至少为解决同位素危机指明了出路，这一危机指月球的化学同位素与地球的如此接近。

Here's the idea. The authors, a team of Japanese scientists, write that maybe in those early days of the solar system the Earth was sloshing with oceans of magma. Then, when the Mars-sized object slammed into those molten seas, their models predict a lot more Earth-derived material got ejected into orbit in the form of scorching⁶ vapors⁷.

想法如下。这篇文章的作者是一个日本科学家小组，他们写道，或许在太阳系早期，地球上到处都是岩浆海。之后，当火星大小的物体撞进这些岩浆海时，他们的模型预测，有更多来自地球的物质以灼热蒸汽的形式被喷射到轨道上。

"Temperatures of tens of thousands of degrees. And so that expands at speeds that exceed the escape velocity⁸ of the earth, and in that way it injects material into orbit around the Earth."

“蒸汽温度高达数万度。蒸汽的膨胀速度超过了地球的逃逸速度，然后以这种方式将物质注入地球周围的轨道。”

That material rapidly coalesces⁹, and bingo, you've got a moon. Melosh says there are still a few kinks to work out in the scenario¹⁰. Still, he says, it's a step forward.

这些物质迅速结合，没错，之后就形成了月球。梅洛什说，这种想象情景仍有一些问题需要解答。不过，他说这是向前迈出的一步。

"Think of it as a major clue in a murder mystery or something like that. It could be a true clue toward the answer or it could be a deception—we don't know yet." So it could be that when astronauts started walking on the moon a half-century ago, they were really leaving footprints on the remains of the primordial¹¹ Earth.

“可以将其想成谋杀案之类的主要线索。这可能是通往答案的真正线索，也可能是场骗局，现在我们还不清楚。”因此，当半个世纪前宇航员开始在月球上行走时，他们可能正在原始地球的遗迹上留下脚印。

Thanks for listening for Scientific American — 60-Second Science. I'm Christopher Intagliata.

谢谢大家收听科学美国人——60秒科学。我是克里斯托弗·因塔利亚塔。