了解宇宙是如何运行的（2010）

How the Universe Works S05E01

Part 5 April 18, 2021, 7:46 p.m.

of these giant balls of gas,
产生火花第一批恒星诞生并开始制♥造♥
and the first stars start to manufacture
许多能组成现在你的汽车的重元素
many of the heavy elements that make up your car today.
最惊人发现
奥尔特云
在太阳系外层的深处
Deep in the outer reaches of the solar system,
远远超出了太阳风
far beyond the last gasps of the sun's atmosphere,
所能涉及到的范围
we are blind.
我们根本看不到那么远
We simply can't see that far.
然而有时我们会从那个地方迎来
But sometimes we get messengers from beyond,
能使生命终结的信使——彗星
potentially life-ending messengers ... comets.
基本上有两种彗星
There's basically two kinds of comets.
一种叫短周期彗星
There's comets that are called short-period comets,
还有一种叫长周期彗星
and the other kind is called long-period comets.
短周期彗星来自柯伊伯带
Short-period comets come from the kuiper belt,
是行星轨道外♥围♥的太空垃圾盘
the disk of space junk just beyond the planets.
它们以相对较小的周期
They travel around the solar system
环绕太阳系运行
in relatively small circles,
并以200年或更少的时间间隔定期返回
returning at regular intervals of 200 years or less.
长周期彗星则有点神秘
Long-period comets are a bit more mysterious.
长周期彗星大约
The long-period comets can come back around
每1000年回来一次
something like every 1,000 years,
甚至100万年回来一次
or even a million years,
和短周期彗星
and unlike the short-period comets
绕着一圈来回不同的是
that come in on sort of circles,
长周期彗星以非常低的轨道来回
the long-period ones come in on really plunging orbits,
它们可以来自四面八方
and they can come in
从不同的方向来回
from all over the place and all different directions.
这告诉我们它们来自不同的地方
And that tells us they come from somewhere different.
我们认为长周期彗星
The long-period comets we think are coming from someplace
是从更远更远的地方
much, much farther away,
时不时地向太阳俯冲
and it's more like a spherical cloud
这个地方更像是
of very distant things
由非常遥远的物体组成的球状云
that are now plunging down into the sun every now and again.
当彗星飞进来时，太阳会把它加热
When a comet comes in, the sun heats it up.
冰变成了气体，彗星失去了质量
The ice turns into a gas, and the comet loses mass.
随着时间的推移，这些彗星会消失
Over time, these comets will disappear,
但它们仍会不断到来
and yet they keep coming.
这就意味着那里一定有很多这样的东西
That means that there must be a reservoir of them out there.
但是在哪里呢？他们来自哪里？
But where is there? Where are they coming from?
对于这些奇怪的彗星，最早的一种解释是
One of the first explanations for these strange comets
它们可能不是来自太阳系
is maybe they're not from our solar system.
也许银河系中到处都是这样的冰块
Maybe the galaxy is full of these icy chunks
它们偶尔会像雨点一样落在我们身上
that occasionally rain down on us.
但后来我们想
But then we thought,
“它们可能来自太阳系的另一个部分”
"maybe they come from another part of the solar system."
也许我们的整个太阳系
Maybe our whole solar system was surrounded
都被最初形成时
by a ball of junk left over
遗留下来的垃圾球包围着
from the very first days of its creation ...
奥尔特云
the oort cloud.
理论上说，太阳系周围一定有一个热液储存库
It was theorized that there must be a reservoir of them,
一个巨大的云，里面有数以百万计
a giant cloud surrounding the solar system, with millions,
甚至数万亿计的冰体
billions, maybe even trillions of these icy bodies.
但我们从未见过
But we've never actually seen it.
所以这个奥尔特云
So this oort cloud,
这个理论上的彗星群，对……这是
this theorized population of comets, is that ...
理论上的
it's theoretical.
它从未被直接观察到
It's never been directly observed.
奥尔特云中的物体非常遥远
The objects in the oort cloud are so far away
又小又暗
and so small and dark
我们从未观测到
that we've never observed something
奥尔特云中的物体
actually out in the oort cloud.
总是有东西掉进来
Something has to fall in.
所以你可以从这些不同的角度
So you see things falling in
观察到物体的下落
from all of these different angles.
从那里，你可以推断出外面的情况
From there, you can deduce what must be out there.
有趣的是，奥尔特云
A fun way to think of the oort cloud
是由从未被使用过的行星碎片组成的
is that these are pieces of planets that never got used.
它们真的是残羹剩饭
They really are leftovers.
奥尔特云实际上并没有附带
The oort cloud actually didn't come with the original package,
原始的信息包
if you will.
奥尔特云的形成是因为
The oort cloud formed when they tried,
它们试图成为那些巨大的行星
but miserably failed, to join the party
但不幸失败了
and become those giant planets,
它们被抛向了不同的方向
and instead got thrown all in different directions,
现在它们存在于离最近一颗恒星一半的地方
and they now exist halfway to the next star.
它们是一个巨大的球形分布
They're a big, giant spherical distribution.
46亿年前，太阳被点燃
4.6 billion years ago, our sun ignites.
一团尘埃和气体云围绕着初生的恒星
A cloud of dust and gas circles the infant star.
然后引力开始发挥作用
Then gravity gets to work,
吸入气体、尘埃、冰和岩石
sucking in gas, dust, ice, and rocks
形成新生的行星
to form the infant planets.
行星是由那些岩石,冰块等
The planets formed out of building blocks,
更小的材料块聚合形成的
smaller chunks of material ... rock, ice...
这些东西都是随着时间积累起来的
Stuff that came together over time.
疯狂的旋转、碰撞的物质
The frenzy of swirling, colliding matter
在小行星带和伊伯带
leaves behind debris as rocky rubble in the asteroid belt
留下了岩石碎片和冰
and ice in the kuiper belt.
然后海王星和天王星也加入进来
Then Neptune and uranus got in on the act,
将碎片进一步分散
scattering the debris out further.
它们中的大多数都被永远地甩出了太阳系
Most of them go thrown out of the solar system forever,
但有些却没有
but the ones that didn't
而是进入了一种巨大而漫长的，长达百万年的循环轨道
go on these big, long, million-year looping orbits,
那就是奥尔特云
and that's the oort cloud.
数以亿计的冰岩
Billions of icy rocks
被抛向四面八方
were thrown out in all directions
直到在整个太阳系周围形成了一个碎片球
until a ball of debris formed around the whole solar system.
奥尔特云彗星
The oort cloud comets
是太阳系形成的恐龙骨骼
are dinosaur bones of solar system formation.
其中包含有
Contained in them are the ingredients
构成我们行星的成分
that went up to make our planets.
奥尔特云的大部分物体
Most of the oort cloud objects
将永远停留在这片冰冷的云中
will stay in this icy cloud forever,
遥远地绕着太阳旋转
orbiting the distant sun.
但也有一些偏离了
But a few get nudged loose,
太阳的引力将它们拉向内部，就像飞蛾扑火一样
and the sun's gravity pulls them inwards like moths to a flame.
像这样一颗彗星可能会悄悄靠近你
And such a comet could sneak up on you,
而你甚至不知道它的存在
and you won't even know it's there.
这些彗星的直径可达数英里
These comets can be many miles across,
它们移♥动♥的速度非常快
and they're moving extremely rapidly,
有时高达每秒100英里
sometimes as much as 100 miles per second.
这使得他们非常危险
This makes them pretty dangerous.
至于有多危险？问一下恐龙
How dangerous? Ask a dinosaur.
有些人认为导致恐龙灭绝的
Some people think that the massive impact
彗地大碰撞可能就是
that killed off the dinosaurs
由巨大的奥尔特云彗星引起的
may have been caused by a huge oort cloud comet.
它们的危险程度
They can be every bit as dangerous
不亚于造成地球生物灭绝的小行星
as the asteroids usually blamed for extinctions on earth.
我们将很少甚至没有警觉，因为我们不知道
We'd have little or no warning because we have no idea what
是什么将它们从奥尔特云向我们扔过来
is hurling stuff out of the oort cloud at us.
最惊人发现
月球的神秘历史
40多亿年以来
For over 4 billion years,
地球和月球围绕太阳运行
the earth and the moon have traced
呈现出一种微妙的舞蹈
a delicate dance around the sun.
但我们的天体伙伴正在逐渐远离
But our celestial partner is gradually slipping away.
有时候，我们会谈论一些可靠的事情
Sometimes, we talk about things that are reliable.
我们说没有什么
We say there's nothing as reliable
比日出更可靠的了，对吧？
as the rising of the sun, right?
我们也可以用同样的方式来思考月球
We can think of the moon in the same way.
它经历了不同的阶段
It goes through its phases.
夜复一夜，年复一年
It's there night after night, year after year.
但事实证明，