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The Moon is a little bit chubby.
其实，月亮有点儿小胖。
It might look like a perfect circle when there's a full moon, but the Moon is really a couple of kilometers wider than it is tall.
满月的时候，月亮看着是个极其完美的圆形，但其实月亮的横向要比纵向宽几千米。
And scientists have spent more than two hundred years trying to unravel exactly why.
科学家已经历时200多年来解密这其中的原委。
Now, new calculations indicate that the Moon's wide waist is a remnant of its earliest dances with young Earth,
如今，最新计算结果表明，月亮看起来比较扁是早期地球跟月球之间的引力作用造成的，
back when Earth might've been covered in a single, global ice sheet.
那时候地球表面可能还是一片冰原。
Any spinning sphere will bulge out around its equator, just due to its inertia.
任何旋转的星体，由于惯性的作用，其赤道附近的区域都会凸出。
But the Moon's equatorial bulge is a bit of a mystery, because it's about twenty times larger than it should be based on its rotation alone.
但月球赤道的突出有点儿迷，因为单从其自转情况来看，其横向大小就是正常情况的近20倍。
And even though we've learned a lot about the Moon in the centuries since the mismatch was discovered,
而且，虽然在这种不匹配的情况发现以来的几百年里，我们对月球的了解已经很多，
scientists still haven't had much luck solving the mystery.
但科学家依然未能解开这个谜团。
Faster rotation leads to larger equatorial bulges, so we've always just kind of assumed that the Moon spun faster when it was very young,
转速越快，赤道的凸出就越明显。基于这一点，我们一直以为月球初期的转速更快一些，
back when it was closer to Earth and still partially molten.
而且那时候的月球距离地球更近，处于部分熔化的状态。
Then, as the Moon cooled, the larger bulge must have frozen in place too. Still, this idea has been hard to conclusively prove.
之后，随着月球的冷却，突起的部分按理来说也一定冻结了，不过，这一观点一直很难得到证实。
There's just so much that we don't know about the early interactions between the Earth and the Moon.
这样的疑团实在太多，所以我们无法得知地球与月球之间早期的互动情况。
A new study published this month in the journal Geophysical Research Letters is a first step in changing all of that.
本月，《地球物理研究通讯》期刊发表了一项新研究。该研究是改变当前疑团重重情况的第一步。
To try and crack the case, the team used computer models to look back in time.
为了解决疑团，该研究小组通过计算机建模来模拟之前的情况。
Specifically, they looked back over four billion years, around the time the Moon first formed.
具体来说，他们回顾了40多亿年之前的情况，那时大概是月球刚刚形成的时间。
The authors modeled the interactions between the Earth and the young, solidifying Moon with lots of different initial conditions,
研究人员模拟了地球与当时处于凝固状态的初生月球之间的互动情况，设定了许多不同的初始条件，
things like how fast both bodies might've spun in those first billion years.
比如地球和月球在最初的10亿年间转速如何等。
What they discovered was a great combination of what everyone expected to find and what no one had ever even really guessed.
他们发现了许多每个人都能预测到，但并未真正有人猜过的情况。
Unsurprisingly, they found that, to produce an equatorial bulge like the one we see today,
毫不意外的是，他们发现，要想实现今天我们看到的这样扁的月球，
the young, partially molten Moon must've been spinning a lot more quickly. Then, as the molten layers froze, the bulge would've frozen in place.
当时处于部分熔化状态的初生月球转速更快，随后，由于熔融层的冻结，相应的凸起也会随之冻结。
But the more unexpected results have a lot more to teach us about the Earth than about the Moon.
但这些意想不到的研究结果所揭示的有关地球的信息却比月球多。
The models indicate that it took a few hundred million years to form the Moon's equatorial bulges, which is longer than scientists had guessed.
建模结果显示，月球赤道部分的凸起形成所需要的时间有几千万年，这比科学家此前的预想长很多。
They also showed that, when the bulges were first formed, the Moon must've still been a lot closer to Earth than scientists had thought.
建模结果还表明，凸起最初形成之时，月球距离地球的距离一定比科学家此前以为的更近。
That actually says a lot about our planet. The Moon has been moving away from Earth ever since it formed.
这些都提供了与地球有关的许多信息，自月球形成以来，其距离地球的距离就越来越远。
And that recession is driven by complex interactions between the Moon and Earth's tides.
这是月球和地球潮汐之间复杂的相互作用引起的。
One consequence of these interactions is that the water on Earth sloshes around and rubs against landforms and ocean floors.
这种相互作用的一个结果是：地球上的海水翻涌，冲撞着各种地貌和海底。
This friction causes the Earth to spin more slowly.
这种冲撞是地球的自转速度降低。
And in turn, that puts more energy in the Moon's orbit, so the Moon moves further away from us.
转而对月球轨道施加了更大的能量，于是月球便逐渐偏离地球。
So if the young Moon stayed closer to Earth for longer than people thought, that means that, among other things,
所以，如果月球一开始离地球的距离比人们想象得更近、保持的时间也更长的话，
those tidal effects couldn't have been nearly as strong as they are today. The authors point out a couple possible solutions for this.
那么这些潮汐作用也不会有今天那么强烈，这些研究人员指出了两种可能性。
One is that the Earth could've been covered in a roughly global ocean with very smooth sea floors.
一种是：地球可能一开始是大片海洋，且海床平滑。
In that case, there wouldn't have been as many features for the water to slosh against, so there wouldn't have been as much friction.
如果是这样的话，就不会有足够的地貌与水进行冲撞，也就不会有这么多的摩擦。
But it's hard to see why Earth would've been smooth enough for this to work, so it's not a great explanation.
但如果海床足够平滑，这种可能性就很难成立，所以这种说法站不住脚。
Still, the other solution the researchers proposed seems a lot more plausible. And it's pretty cool.
不过，研究人员提出的另一种说法似乎可能性更强，听着也合情合理。
See, there's already a lot of evidence that the Sun was about 30% cooler four billion years ago,
有很多证据表明：40亿年前的太阳温度比现在低了近30%，
and that Earth probably didn't have enough greenhouse gases to trap much heat.
而且地球上的温室效应不够强，所以无法留住很多热量。
So, according to the paper's authors, all of Earth's surface water could've been locked up in a worldwide ice sheet,
基于此，该论文的研究人员认为，地球表面的所有水资源可能都在全球范围的冰原里锁住了，
known among scientists as a Snowball Earth event.
这种现象在科学界名为“雪球地球”假说。
If all the water were frozen, there would be almost none of those complex tidal interactions between the Earth and the Moon.
如果所有的水都结成了冰，地球与月球之间由潮汐引起的复杂互动也就不存在了。
So the Moon wouldn't have moved away as quickly. We have evidence for a Snowball Earth around 650 million years ago,
月球也就不会以这样快的速度偏离地球，我们有证据表明，雪球地球现象曾在大约6.5亿年前出现过，
but this is the first evidence for something like it happening very early on around four billion years ago.
但这是第一次有证据表明雪球地球这样的现象发生于更早的时候，大约40亿年以前。
The paper's model is one of the first of its kind, so it'll almost definitely be refined over time.
该论文的模型是另辟蹊径，所以以后肯定还会有这种类型的论文对其进行补充。
But for now, it suggests that we should be ready to rethink some of our ideas about the early history of both the Moon and the Earth.
但就目前来讲，该论文表明，我们应该重新思考月球和地球初期的情况。
And look, all this happened because we were curious why the Moon had a little bit of extra bulge.
之所有有这样的发现是因为我们一开始好奇月球为什么会有凸起。
And if we hadn't had the moon, we wouldn't have this amazing glimpse into the early history of our planet.
而如果没有月球，我们就不会出乎意料地了解到地球的早期历史。
Thanks Moon! And thank you for watching this episode of SciShow Space!
这里要感谢月球！也要感谢大家收看本期的《太空科学秀》！
If you would like to learn more about Moon research, you can check our video about three more Moon mysteries we're still trying to figure out.
如果您想了解更多有关月球的研究，还有三则视频讲解了我们正在探索的与月球有关的奥秘。
