了解宇宙是如何运行的（2010）

How the Universe Works S06E04

Part 5 Dec. 22, 2021, 7:22 p.m.

dust, and rocky material.
较轻的气体更容易落入中心
The lighter gas falls into the center more easily,
形成行星
forming the planet,
而一些较重的岩石物质
while some of the heavier rocky material
留在圆盘上，形成卫星
is left over in the disk, forming the moons.
通常情况下，卫星的运行方向
Typically, the moon travels in the same direction
与行星的运行方向相同
that the planet is orbiting,
但在海卫一和海王星的情况
but in the case of Triton and Neptune,
却是完全相反的情况
that's the complete opposite case.
我们知道它不可能
We know it couldn't have formed
在海王星周围的轨道上形成
in that orbit around Neptune.
它一定来自其他地方
It had to come were somewhere else,
而关于它来自哪里的一个奇妙线索
and a wonderful clue to where it came from
就是附近的邻居，冥王星
is the nearby neighbor, Pluto.
冥王星是柯伊伯带附近的一颗矮行星
Pluto is a dwarf planet in the nearby Kuiper belt.
它只比海卫一小200英里
It's only 200 miles smaller than Triton,
但这两个天体的相似之处并不仅仅在于它的大小
but it's not just size that makes these two bodies similar.
而是他们的成分
It's their composition.
海卫一实际上与冥王星最为相似
Triton is actually most similar to Pluto.
它的内部有类似数量的岩石
It has a similar amount of rock in its interior.
它表面成分也类似
It has a similar surface composition
含有大量的氮和甲烷
with a lot of nitrogen and methane.
它看起来真的很像一个类冥王星的世界
It really looks like a Pluto-like world,
但它只是围绕着一颗行星运行
but it just happens to be orbiting a planet
而不是围绕太阳运行
instead of orbiting the Sun.
如果海卫一和冥王星一样
If Triton is like Pluto,
也许它也是在柯伊伯带诞生的
maybe it also started life in the Kuiper belt.
它会不会被海王星的引力捕获
Could it have been captured by Neptune's gravity,
被拉进这颗气体巨星的轨道呢？
pulled into the gas giant's orbit?
要把了卫星捕获到围绕行星的轨道上并不容易
It's not easy to capture a moon into orbit around a planet.
一个物体靠近另一个世界然后螺旋进入
It's not natural for a body to come close to another world
这是不自然的
and just spiral in.
当它靠近的时候你得想办法刹住车
You've somehow got to put on the brakes when it's close in.
海王星要想捕获海卫一
For Neptune to capture Triton,
就必须减慢海卫一的速度，但如何减慢呢？
Triton had to be slowed down, but how?
柯伊伯带的物体再次提供了线索
Again, Kuiper belt objects hold a clue.
许多最大的行星都是双星
(指在柯伊伯带中)
Many of the largest are binary pairs,
即两个互相环绕的世界
two worlds orbiting each other,
比如冥王星和它的大卫星冥卫一
like Pluto and its large moon Charon.
也许海卫一也是其中之一
Perhaps Triton was one of a pair as well.
如果海卫一和另一个伙伴
If Triton was in orbit with a partner,
一起在轨道上运行，那么每一对都将以不同的速度运行
each of the pair would travel at different speeds.
这种速度差异是关键
This speed difference is key.
海卫一的速度稍微慢一点
Triton's velocity is just a little bit slower.
由于它在绕着它的伴星旋转，它的速度足够慢
As it's orbiting its companion, it's slow enough
以至于可以被海王星捕获
that it could actually get captured by Neptune,
而另一个则被海王星加速穿过太阳系
while that other one would speed off across the solar system.
海卫一原来的舞伴
Triton's original dance partner
被甩了出去
is flung out and away.
海卫一有了一个更大的新伙伴，海王星
Triton has a new, much bigger companion, Neptune.
但这些看似不可能的伙伴却不同步
But these unlikely partners are dancing out of sync.
捕获解释了向后的轨道
Capture explains the backwards orbit,
但还有一个更奇怪的谜题需要解决
but there's an even stranger mystery to solve.
在海卫一这样的卫星上
On a moon like Triton,
我们预计会看到大量坑洞地形
we'd expect to see heavily cratered terrain,
这是地质上死亡世界的标志
the hallmark of geologically dead worlds.
然而恰恰相反，旅行者2号♥ 揭示了一个惊人的活着的世界
Instead, voyager 2 reveals a world that's startlingly alive.
我认为整个旅行者任务中
I think one of the most amazing discoveries
最惊人的发现之一就是在飞过海卫一时
of the entire voyager mission is that when we flew past Triton,
我们看到这些液氮喷流
we saw these jets of liquid nitrogen
从海卫一表面喷涌而出
coming up out of the surface.
我们不知道这个又小又冷的世界
We had no idea that this tiny, little cold world
竟然还“活着”
out there would still be alive.
光滑的冰覆盖在星球表面
Smooth, icy planes cover the surface.
氮气间歇泉穿过地壳向上喷射
Geysers of nitrogen punch up through the crust
向天空喷出5英里的黑色尘埃
and spew black dust 5 miles into the sky.
我们一直以为它离太阳太远，太冷，太死气沉沉
We thought it was too far from the Sun, too cold, too dead.
它只是一个
It was just going to be an ice ball
像其他卫星一样的冰球，然而，不是
like all the other moons that had tended to be, but, no.
这是一个新鲜，年轻的表面
It's a fresh, young surface.
海卫一的表面
Triton's surface is
是零下200度的冰点
a frosty 200 degrees below freezing.
驱动这些地表特征的热量从何而来？
Where's the heat coming from to drive these surface features?
答案就在于海王星对海卫一的捕获
The answer lies with Neptune's capture of Triton.
海卫一的轨道是圆形的，但它曾经是椭圆形的
Triton's orbit is circular, but it was once elliptical.
当海卫一不断靠近或远离时
As Triton moved closer in and farther away,
它会不断受到海王星引力的
it would have been repeatedly squashed
挤压和拉伸
and stretched by Neptune's gravity.
这将在海卫一内部
That would generate massive amounts of friction
产生大量摩擦
inside of Triton.
在这些力量的作用下，海卫一
Might well have completely melted Triton
可能会完全融化
due to those forces,
当这种情况发生时，它会起到刹车的作用
and as that happened, it would have acted as a brake.
所有这些摩擦会使海卫一的轨道变成圆形
All that friction would have circularized Triton's orbit
并使它留在我们今天看到的轨道上
and left it in the orbit that we see today.
正是这种轨道上的变化给了海卫一热量
This change in orbit is what gives Triton its heat.
海卫一的表面被冻住了
The surface of Triton froze over,
但这颗卫星在冰壳的深处
but the moon still retains some of this warmth
仍然保留着一些温暖
deep below the icy shell.
天文学家认为有足够的热量将冰融化成水
Astronomers think there's enough heat to melt ice into water,
在距离太阳30亿英里的地方
forming an underground liquid ocean
形成一个地下液态海洋
on a world 3 billion miles from the Sun.
液态水、热量……有一个问题
Liquid water, heat... There is only one question,
不提出来是不可能的了
and it's impossible not to ask it.
会有生命存在吗？
Could there be life?
如果海卫一上有能量来源
If there's a source of energy on Triton,
那么也许有某种生命知道
then perhaps there's a form of life that figured out
如何利用这种能量来源
how to take advantage of that energy source.
令人难以置信的想法
An incredible thought.
如果有生命存在，这个冰冻的球体
If life has carved out a niche, this frozen ball
可能就是离太阳最远的宜居世界
could be the most distant habitable world from the Sun.
海王星的卫星，海卫一，可能还活着
Neptune's moon, Triton, might be alive,
但天王星的卫星更奇怪
but Uranus' moons are even stranger.
他们有一个巧妙的伎俩来欺骗你他已经死亡
They have a neat trick to cheat death entirely.
天王星……一个有着美丽的、闪烁的光环
Uranus... An ice giant with beautiful,
和27个卫星的冰巨人…
shimmering rings and 27 moons...
它们的位置是个谜
And their position is a mystery.
其中一半在于紧密排列的轨道中
Half exist within a tightly packed orbit.
这么多卫星不可能
It shouldn't be possible for this many moons
如此接近彼此
to be in such close proximity to each other.
天王星周围的环境非常繁忙
The environment around Uranus is very busy,
而且系统看起来并不稳定
and the system appears unstable,
卫星应该在碰撞
and the moons should be colliding,
但是，我们看到的是些漂亮的，结构良好的卫星
but yet, we see these nice, well-formed moons.
更令人惊讶的是，在2003年
And what's even more surprising is that in 2003,
哈勃太空望远镜发现了两个新环
the Hubble space telescope revealed
和两个新卫星……丘比特和马伯
two new rings and two new moons... Cupid and Mab.
问题来了，这些卫星从何而来？
Question is, where did these moons come from?
线索就在天王星的光环中
A clue lies in Uranus' rings.
除了拥挤的卫星系统外
In addition to the very packed moon system,
天王星周围还有光环
you also have rings around Uranus,
这也有些出乎意料
which is also somewhat unexpected,
但这两个出乎意料的特质
but these two unexpected qualities
或许可以相互解释
might actually explain one another.
任何时候你所看到一个环系统，其实你看到的是一个过程的一部分
Anytime you see a ring system, you're seeing part of a process.
在地球的历史上可能有一段时间
There was probably a time in Earth's history
它有一个环，你知道吗，那时我们的月球正在形成
when it had a ring, you know, when our moon was being formed.
这些新卫星似乎是由以前的
It seems that the new moons are made up of material
光环系统的物质组成的
from a previous ring system.
但当科学家们为丘比特的未来做模型时
But when scientists model Cupid's future,