了解宇宙是如何运行的（2010）

How the Universe Works S06E04

Part 1 Dec. 22, 2021, 7:22 p.m.

我们的太阳系是巨行星的家园
Our solar system is home to giants.
气态巨行星木星和土星似乎占据主导地位
Gas giants Jupiter and Saturn seem to dominate,
但这两颗冰巨星决定了其他行星的命运……
but two ice giants determine the fate of the rest...
海王星和天王星……
Neptune and Uranus...
这些遥远的行星与我们毫无关联
Distant planets unconnected to us,
至少我们是这么认为的
or so we thought.
我们现在知道冰巨人的命运
We now know the fate of the ice giants
与我们息息相关
is entwined with our own.
它们从冰冷，沉闷的世界
They've gone from being these cold, dull worlds
变成了真正拥有你和我
to actually having in them the very secret
为什么存在的秘密
of why you and I exist at all.
他们的故事是史诗般的迁徙
Their story is of epic migration,
残酷的破坏…
brutal destruction...
天王星被猛击，然后被撞到一边
Uranus got jabbed and then knocked on its side.
……比任何人想象的都鲜活的世界
...Of worlds more alive than anyone imagined.
它们掌握着太阳系历史的钥匙
They hold the key to the history of the solar system
甚至可能是地球上生命的钥匙
and perhaps to life on Earth.
宇宙是如何运行的
第六季第四集天王星与海王星……冰巨人的崛起
天王星和海王星……
Uranus and Neptune... Mysterious giants
潜伏在寒冷的太阳系外♥围♥的神秘的巨人……
lurking in the cold outer reaches of the solar system...
离太阳最远的行星
The farthest planets from the Sun.
天王星和海王星可以说是
Uranus and Neptune are sort of the sentinels
太阳系外♥围♥的哨兵
of the outer solar system.
它们越过木星和土星
They're out past Jupiter and Saturn,
距离太阳大约有20亿到30亿英里
well over, like, 2 billion, 3 billion miles from the Sun.
它们的大小和位置
Their size and location
对行星天文学家来说是一个谜
are a puzzle to planetary astronomers.
天王星和海王星有点神秘，因为在某种程度上
Uranus and Neptune are somewhat of a mystery because,
它们不应该存在
in a way, they shouldn't exist,
或者至少它们不应该存在于它们所在的地方
or at least they shouldn't exist where they are.
科学家们无法理解
Scientists can't understand
这些巨大的行星是如何变得如此之大，离太阳又是如此之远
how these giant planets grew so big so far from the Sun.
这个谜团始于45亿年前……
The mystery starts 4 1/2 billion years ago...
……随着太阳系的诞生
...with the birth of the solar system.
一开始，太阳由一个由气体和尘埃
In the beginning, the Sun ignites from a disk
组成的圆盘点燃
of gas and dust.
第一批行星的岩石内核开始成长
The rocky cores of the first planets start to grow.
它们在绕太阳公转的过程中与圆盘上的碎片相撞
They collide with the debris in the disk as they orbit the Sun.
但内行星有大小限制
But the inner planets have a size limit.
要成长为一个巨大的行星，就需要气体
To grow into a giant planet, you need gas.
来自初生太阳的热量将这些较轻的气体分子
Heat from the infant sun blasts these lighter gas molecules
喷发到天文学家称之为雪线的范围之外
beyond a point astronomers call the frost line.
这里的温度足以让氢和氦等气体分子
Out here, it's cool enough for gas molecules like hydrogen
稳定下来
and helium to stabilize.
木星和土星最先成形
Jupiter and Saturn take shape first...
吞噬着丰富的气体，迅速成为气态巨行星
Sweeping in the abundant gas and quickly becoming gas giants.
但是海王星和天王星不一样
But Neptune and Uranus are different.
木星和土星的氢和氦含量约为90%
Jupiter and Saturn are about 90% hydrogen and helium,
而海王星和天王星的氢和氦含量更接近20%
whereas Neptune and Uranus are more like 20%.
那么气体中的这种差异
So what does this difference in gas tell us
告诉了我们什么呢？
about their formation?
我们怀疑天王星和海王星出现得稍晚一些
We suspect that Uranus and Neptune came a little bit later
因为那里没有那么多的气体可以被收集
when there was not as much gas to be swept up.
在氢气和氦气消失之前，天王星和海王星
Uranus and Neptune have less time to suck up
能吸收的氢气和氦气的时间并不多
as much hydrogen and helium before these gases disappear.
但由于它们是在更远的地方形成的
But they're also forming farther out,
那里足够冷，其他更重的气体可以冻结
where it's cold enough for other, heavier gases to freeze.
这些气体被不断增长的外行星扫荡一空
These are swept up by the growing outer planets.
在天王星和海王星所在的地方，有成吨♥的冰
Out where Uranus and Neptune are, tons of ice,
我们所认为那是成吨♥的冰冻气体……
tons of frozen gases as we might think of them...
甲烷，氨，水
Methane, ammonia, water,
这就是这些重气体的主要组成成份
and so that's what makes up their composition predominantly.
也许它们比木星和土星要小
They may be smaller than Jupiter and Saturn,
但这些重冰意味着它们的密度会增大
but these heavy ices mean they grow dense.
它们变成了冰巨人
They become ice giants.
但有个问题
But there's a problem.
他们太大了
They're too big.
新生恒星周围由气体和冰组成的圆盘
The disk of gas and ice around a newborn star
不会永远存在下去
does not last forever,
而太阳系深处的物质
and material in the far reaches
分布得很薄
of the solar system is spread thin.
当你在太阳系中走得更远时
As you move further out in the solar system,
两个天体相互碰撞
the time scale for two bodies
和吸积的时间就会变慢
to find each other and collide and accrete slows down
因为太阳外♥围♥的公转周期要长得多
because the periods around the Sun are much longer,
这需要非常非常长的时间
and it just takes a very, very long time.
海王星和天王星围绕太阳运转的速度非常慢
Neptune and Uranus orbit the Sun incredibly slowly,
以至于无法与足够多的冰物质发生碰撞
too slowly to collide with enough icy material
从而形成我们今天看到的巨行星
to grow into the giants we see today.
所以当我们在这个非常遥远的轨道上观察海王星时
So when we look at Neptune at this very distant orbit,
太阳系这个轨道应该没有足够的时间
we don't have enough time in the solar system
来建造一个像海王星这样的行星
to build a planet like Neptune.
当然只是我们认为在现在发现的地方建造海王星
We just don't think we could build Neptune
是一件不可能的事
where we find it today.
当天文学家开始发现围绕其他恒星运行的行星时
海王星令人困惑的位置出现了一条线索
研究其他恒星周围的行星
最大的惊喜之一
就是海王星质量的行星在其他恒星周围非常常见
但他们都不在我们发现海王星的地方
事实上，我们在其他恒星周围发现的是
海王星质量的行星，它们非常普遍
但却非常接近恒星
非常接近于我们太阳系内水星的轨道
在我们的太阳系中
海王星和天王星离太阳远得不可思议
而在其他恒星系中
冰巨行星离它们的恒星近得不可思议
那么发生了什么？
So what happened?
事实证明，我们现在看到它们的地方
It turns out, where we see them now
很有可能不是它们最初的地方
is probably not where they started out.
我们了解到的关于太阳系的一件事
One thing we've learned about solar systems
就是事物处于一种微妙的平衡中
is that things are in a delicate balance,
行星会迁移，他们会移♥动♥
and planets migrate. They move around.
它们不会在一个地方形成并永远停留在那里
They don't form in one place and stay there forever.
那么，是什么有足够的力量
So what has enough power
来移♥动♥像海王星这样的巨大行星呢？
to move a giant planet like Neptune?
一个更大的行星……木星
An even bigger one... Jupiter.
行星有一种运动的方式
One way for planets to move
是通过相互作用的引力
is by gravitationally interacting with each other,
所以它们能感受到彼此的引力
so they feel each other's gravity.
引力可以拖拽，也可以拉动，这种效应会导致
They can tug. They can pull, and that effect can lead to planets
行星在它们的行星系统中缓慢迁移
slowly migrating around in their planetary systems.
在太阳系形成初期，巨行星之间的距离
The closer two planets are, the greater the effect,
要近得多，两颗行星离得越近
and in the early days of the solar system,
他们之间的这种影响力就越大
the giant planets are much closer together.
最重要的是，它们的轨道排列顺序
On top of that, they may have orbited
可能与我们今天看到的并不同……
in a different order than we see today...
木星、土星、海王星和天王星
Jupiter, Saturn, Neptune, and Uranus.
那么是什么导致海王星和天王星交换了位置呢？
So what causes Neptune and Uranus to swap positions?
答案在于木星和土星
The answer lies with Jupiter and Saturn.
这两颗最大的巨行星上演了一场引力之舞
The two biggest giants lock into a gravitational dance.
它们之间总是有这种相互作用
There's always this interplay between them.
想想卡波耶拉舞的舞者，他们的平衡和移♥动♥
Think of Capoeira dancers, balancing and moving together
就是一种精心安排的方式
in a careful, orchestrated way.
经过数百万年，一种节奏慢慢形成
Over millions of years, a rhythm slowly builds.
这些巨行星♥相♥互推拉
These giants push and pull each other
并进入更椭圆的轨道
into more elliptical orbits.
当重力之舞达到高♥潮♥后
But the gravitational dance reaches a climax.
拉伸轨道变得不稳定
The stretched orbits become unstable.
巨人们偏离了航向
The giants move off course.
当土星和木星远离太阳时
As Saturn and Jupiter twist out from the Sun,
它们就把海王星抛到天王星的外面
they fling Neptune out beyond Uranus.
当海王星穿越太阳系时
As Neptune moves out through the solar system,
它会把碎片推到它前面
it pushes debris ahead of it.
这些都是行星形成时剩下的冰碎片
These are the leftover icy fragments from planet formation.
海王星会把这些尸体铲出来