了解宇宙是如何运行的（2010）

How the Universe Works S08E01

Part 8 Jan. 30, 2022, 2:57 p.m.

by using radio detection
and ranging,
已经达到了这种精度水平
more commonly known
as radar.
阿雷西博天文台的行星雷达系统
The planetary radar system
at arecibo observatory
是世界上最强大的雷达系统
is the most powerful
radar system in the world.
我们关注的是那些有潜在危险的小行星
We focus on
potentially hazardous asteroids,
它们很有可能会撞击地球
which are those that have a high
probability of impacting earth.
阿雷西博向这颗新发现的小行星
Narrator: Arecibo sends out
radio signals
发射无线电♥信♥♥号♥♥
toward the newly
detected asteroid.
萨特:它发射无线电♥信♥♥号♥♥
Sutter:
It emanates radio signals.
其中一些碰到了小行星，就像警♥察♥的雷达枪
Some of them hit the asteroid
just like a radar gun from a cop
碰到你的车子一样
might hit the side of your car.
桑布拉诺-马林:这是非常相似的
Zambrano-marin:
That's pretty similar,
但我们不是用小尺度的雷达枪
but instead of doing it
with a radar gun
而是用1兆瓦的功率
on the small scale, we're
doing at a really big scale
来击中几十个月球距离
with one megawatt power
hitting objects that are
以外的物体
tens of lunar distances away.
萨特:然后这些无线电波反射回地球
Sutter: And then those radio
waves bounce back to earth
我们再次检测它们，通过比较
and we detect them again,
and by comparing the differences
我们发送的和接收到的信息之间的差异
between what we sent
and what we received,
我们可以得到一张小行星的地图
we can get a map
of the asteroid itself
这样就可以知道它移♥动♥的位置和速度
and we can get where it's moving
and how fast it's moving.
速度、大小和撞击地点
Narrator: Speed, size,
and location of strike
决定了小行星撞击的结果
determine the outcome
of an asteroid impact.
但小行星的类型是另一个因素
But the type of asteroid
is another factor.
它可能意味着生存
It can mean the difference
between survival
或完全灭绝的区别
or complete annihilation.
♪
白令海小行星在大气层中爆♥炸♥了
narrator:
The bering sea asteroid
blew up in the atmosphere,
但巴林杰陨石坑小行星以其全部力量
but the barringer crater
asteroid hit the ground intact
完好无损地撞击了地面
with its full force.
为什么不同的小行星表现不同？
Why do different asteroids
behave differently?
阿波菲斯朝我们来的时候会怎么做？
And what will apophis do
when it heads our way?
阿雷西博的雷达可能有答案
Arecibo's radar
may have the answer.
当我们从这些物体反射雷达波时
When we bounce radar waves
off of these objects,
我们可以有效地得到
we can get effectively imagery
of the surface
一些小物体表面的图像
of some of these small objects
这是光学望远镜无法做到的
that we just cannot do
with optical telescopes.
这是阿波菲斯的雷达图像
Narrator: This is
the radar image of apophis.
因为距离太远，他们只能拍到几个像素
It's so far away that all they
could image were a few pixels.
这是阿波菲斯小行星的
So this is our most recent
radar image
最新雷达图像
of asteroid apophis.
你可以看到它只有几个像素
And you can see
it's only a few pixels,
但它确实给了我们关于
but it does give us
information
它到底是什么的信息
on what it actually is.
这少量的像素足以计算出
Narrator: These few pixels
are enough to work out
阿波菲斯的大小
how big apophis is.
维尔克:从这幅图像中，我们可以把它的尺寸
Virkki: From this image,
we can constrain the size
限制在1000英尺左右
to be about 1,000 feet,
这和阿雷西博射电望远镜的尺寸
which is about the same size
as the arecibo
差不多
radio telescope.
所有这些都来自于一堆像素
All of that from what were
a bunch of pixels.
♪
了解小行星的大小和质量
narrator: Knowing the size
and mass of an asteroid
对于了解小行星的构成至关重要
is critical to understanding
what an asteroid is made of.
如果我们知道了体积和质量，就得到了密度
If we have the size and
the mass, we get the density.
如果我们知道密度，我们就能知道它是由什么组成的
If we have the density,
we know what it's made of.
岩石有一定的密度与金属的密度不同
Rock has some density.
Metal has a different density.
因此，我们可以通过雷达探测
So we can determine
a huge amount about the asteroid
来确定这颗小行星的大量信息
simply by pinging it
with radar.
阿雷西博的数据显示
Narrator: Arecibo's data reveals
并非所有的小行星都是相似的
that not all asteroids
are alike.
并不是只有一种小行星
There's not just
one kind of asteroid.
实际上有好几种
There are actually
several kinds,
理解这一点很重要
and this is important
to understand
因为它们的行为不同
because they behave differently.
如果他们影响我们，他们的行为就会不同
They behave differently
if they impact us,
如果我们试图阻止它们影响我们
and they behave differently
if we're trying to prevent them
它们的行为也会有所不同
from impacting us.
我们需要知道这些小行星是由什么组成的
We need to know what these
asteroids are made of
如果它们要撞击地球
if they're gonna hit
the earth
这会极大地改变潜在的影响
because that drastically alters
the potential effects.
小行星的形状、大小和组成各不相同
Asteroids come in different
shapes, different sizes,
我们认为这是因为
and different compositions,
and we think that is
它们是行星形成的产物
because they are the leftovers
of planet formation.
为了了解每颗小行星
Narrator: To understand how
each asteroid formed
是如何形成的以及它们的威胁程度
and their threat level,
we have to go back
我们必须回到46亿年前的太阳系诞生之初
4.6 billion years to the start
of the solar system.
今天我们太阳系中
The reason that there are
all these asteroids
有这么多小行星的原因
floating around
in our solar system today
是因为太阳系形成时的
is just because of the early
violence of the solar system
早期暴♥力♥
as it was forming.
太阳系诞生之时
Narrator: At the birth
of the solar system,
太阳被点燃了
the sun ignites,
留下一个由气体和尘埃组成的圆盘
leaving a disk of gas and dust.
慢慢地，随着时间的推移，行星形成了
Slowly, over time,
planets form.
有大量的行星
Lots of planets.
萨特:早期的太阳系是一个混乱的地方
Sutter: The early solar system
was a messy place.
有更多的行星，更多正在形成的行星
There were a lot more planets,
a lot more forming planets.
它们会相互碰撞
They would crash in
to each other,
它们会合并，它们会分解
they would merge,
they would disintegrate,
它们会重新组合
they would re-form.
这个形成行星世界的过程
This process of accretion
of building planetary worlds
并不只是，你懂的，温和而快乐的
was not just, you know,
kind of gentle and happy.
这是暴♥力♥
It was violent.
这就像一场巨大的宇宙台球游戏——