了解宇宙是如何运行的（2010）

How the Universe Works S01E08

Part 4 April 18, 2021, 7:58 p.m.

This means it didn't
form like most moons
从行星诞生时留下的星尘形成
out of the debris left over
from the birth of the planet
否则它应该转往同一方向
or it would orbit in the same direction.
所以有些反常
So something wasn't right.
海卫一很巨大、轨道奇特、很反常
Triton is huge, and its orbit
is funny. it's anomalous.
不似是和海王星同出一系
It does not seem as though it formed
as a part of the Neptune system.
比较像是颗被俘掳的行星
It seems much more
like a captured planet.
科学家现时相信海卫一曾是矮行星
Scientists now think Triton
was once a dwarf planet
像冥王星一样
like Pluto.
以海王星这么巨大的行星
And a giant planet like Neptune
certainly has enough gravity
它的引力当然足以俘掳海卫一
to capture a moon the size of Triton.
海卫一几可肯定在外太阳系形成
Triton was almost certainly formed
way out in the outer solar system,
然后被海王星俘掳
and then at some point
was captured by Neptune.
海卫一可能曾经拥有一颗卫星
Perhaps Triton early
on had its own moon.
两颗星同时被俘掳
They both were captured,
卫星在俘掳过程中毁灭
and then that moon was destroyed
during the capture process.
但海卫一也有危险
But Triton is in danger,
海王星正把它越拉越近
Neptune is dragging
it closer and closer.
终有一天, 距离太贴近
Eventually, it will get too close...
便会被海王星强大的引力摧毁
and Neptune's immense
gravity will tear it apart.
海卫一便会变成行星周围的环状体
Triton, the moon, will be reborn
as a ring system around the planet.
但我们的卫星月球呢?
But what about our moon?
它从何而来? 是否被俘掳呢?
How did it get there? Was it captured?
事实比想象中更加离奇
The truth is even more extraordinary.
它是在极端狂暴的环境中诞生
It was born in extreme violence.
月球像大部分卫星一样
Our moon, like a lot of moons, is rocky,
布满岩石、荒芜、有很多撞击坑
barren and pockmarked with craters.
但在某一方面, 却又与别不同
But in one way, our moon is
unique in the solar system.
长久以来, 天文学者都以为
For a long time, astronomers thought
月球由地球诞生后留下的星尘形成
the moon formed from debris left
over from the birth of the Earth.
但1960年代的研究员提出不同见解
But researchers in the 1960's came
up with a radically different idea.
他们认为是强大撞击的结果
They suggested it came
from a giant impact
初次提出月球
When we first had the idea
因撞击而形成时
of forming the moon from a giant impact,
并不受大众欢迎
that was not a terribly popular idea.
有些科学界好朋友和同事对我说:
And I actually did have good science
friends, colleagues, coming to me, saying,
应该先详尽考虑各种缓慢进化理论
"You know, we really have to exhaust
all the, the slow evolutionary theories
然后才谈大灾难也不晚
before we start talking
about cataclysms."
比尔夏文需要的证据在月球上
The evidence Bill Hartman
needed was on the moon itself.
等到1969年太阳神登月才找到
And the proof had to wait until Apollo
astronauts finally went there in 1969.
他们把数以百磅的月球石带回来
They brought back hundreds
of pounds of moon rocks.
科学家分♥析♥岩石后, 啧啧称奇
Scientists analysed the
rocks and were amazed.
岩石和地球的地壳一模一样
They were identical to
rocks in the Earth's crust...
而且热力强大
and they'd been superheated.
地球的地壳怎会变热和跑上月球?
So how did pieces of the Earths crust
become super hot and wind up on the moon?
夏文自认可以解答
Hartman was pretty sure he knew.
地球形成时, 有东西撞击它
This whole idea was that the Earth
forms, now you hit it with something,
把上面轻巧的岩石吹走
you blow all this light
rocky material off the top,
它们便环绕地球运行, 成为卫星
that material goes into
orbit and makes the moon.
卫星由岩石碎砾形成
The moon's just made
out of rocky debris.
试想像45亿年前太阳系的混沌情况
Imagine our chaotic solar system
four and a half billion years ago.
年轻的地球是一百多颗新行星之一
The young Earth is just one of a hundred
or so new planets orbiting the sun.
有颗行星叫忒伊亚, 像火星一样大
One of them is a Mars-sized
planet called Theia,
和地球处于碰撞轨道
and it's on a collision
course with Earth.
结果以数千英里时速相撞
They smash into each other at
many thousands of miles an hour.
忒伊亚被毁灭, 地球一息尚存
Theia is destroyed, and
Earth barely survives.
撞击力把数十亿公吨♥星尘射入太空
The impact blasts billions of
tonnes of debris into space.
地球的引力把它们拉入轨道
The Earth's gravity pulls it
into orbit around the planet.
于是地球的碎屑集结, 形成月球
Now these hunks of leftover Earth
clump together and form our moon.
这是科学理论, 但如何测试?
That's the theory, anyway. But
how do you test it for real?
在太空总署的虚拟射击场
Here at NASA's vertical gun range,
科学家重组这场远古的撞击事件
they're recreating that
ancient collision in a lab.
这座30英尺长的大炮
This 30-foot long gun fires
以18,000英里时速发射一颗小弹丸
a tiny projectile at
18,000 miles an hour.
这颗弹丸代表忒伊亚
The projectile is Theia.
这个球体代表地球
This ball represents the Earth.
只要改变忒伊亚的撞击角度
By changing the angle of Theia's impact,
便可以计算出到底需要多大撞击力
the team can figure out how precise
the ancient collision had to be...
才创造出月球
in order to make the moon.
第一次发射, 只在地球表面擦过
In the first shot, Theia hits the
top of the Earth with a glancing blow.
这是浮游在太空中的地球
So here's the Earth, if you
will, just suspended in space.
它受到撞击
And now it's gotten hit
地球喷出一些物体
So now we see the planet, the ejecta
is being ripped out of the Earth
形成巨大的撞击盆地
and is forming this giant impact basin.
如果真的在地球发生
And if this really were the Earth,
盆地宽度达数千公里…数千英里
this basin would be thousands of
kilometres, thousands of miles across.
在这次模拟实验, 只撞出少许地表
In this simulation, Theia only skims
off the surface of the planet...
射出少量星尘出太空
and very little debris
is thrown out into space.
不足以形成月球
Not nearly enough to build our moon.
第二次发射是迎头撞击
The second shot is a head-on collision.
呯, 地球就此消失
Ka-pow, that's the end of
planet Earth, it's gone.
部分星尘会飞出太阳系以外
Some of the debris is gonna
go out of the solar system,
部分星尘会重新吸积
some of the debris will re-accrete
形成太阳系内一些小小星子
to form small planetesimals
within the solar system.
地球不再存在
There's no Earth left,
没有引力可收集星尘, 去形成月球
so there's no gravity to gather
the debris and form the moon.
现在大炮校准在适当角度
Now the gun is set to
just the right angle,
在轻轻擦过和直接撞击之间
halfway between a glancing
blow and a direct hit.
看看地球勉强存活下来的结果
So we'll see what happens
if the Earth barely survives.
噢, 美妙! 哗, 厉害!
Oh, oh, gorgeous! Oh, my gosh, ka-pow!
现在有整片地壳给炸掉
Now we have the entire part of
the Earth being ripped apart,
但喷出的烟雾…厉害!
but the vapour plume is...Oh, my gosh!
太好了
Jeez! That is gorgeous.
这就是月球的起源
But this was the beginning,
the beginning of our moon.
实验证明忒伊亚可能撞向地球
The experiment shows that Theia
could have smashed into the Earth
于是创造了月球
and formed the moon.
不过撞击力必须恰到好处
But the collision had to be just right.
幸好也确实如此
And lucky for us, it was.
今天, 月球在地球25万英里外运行
Today, the moon orbits
250,000 miles from Earth.
但月球初诞生时
But when it first formed,