了解宇宙是如何运行的（2010）

How the Universe Works S08E01

Part 15 Jan. 30, 2022, 2:57 p.m.

Narrator: Leading this
groundbreaking mission to bump
将一颗小行星撞离轨道的是安迪·张博士
an asteroid off its orbit
is dr. Andy chang.
张博士: Dart 是我们做的第一个
Chang: Dart is the first
planetary defense mission
行星防御任务，我们将航♥天♥器
that we've ever done,
where we take a spacecraft,
发射到小行星上，改变它的轨道
we fly the spacecraft into
the asteroid to change
然后让它错过地球
its course and make it
miss the earth.
Dart 的目标是一块525英尺高的太空岩石
Narrator: Dart's target
is a 525 foot space rock
其围绕着巨大的近地小行星迪蒂莫斯运行
orbiting the large
near earth asteroid didymos.
我们选择近地小行星迪蒂莫斯作为 dart 的任务目标
We pick the near earth asteroid
didymos as a target
因为尽管它是一个近地小行星
for the dart mission because
although it's
但它是一颗非常安全地
a near earth asteroid,
it's one that's very safely
停在太空中的小行星
parked away out there in space.
我们不可能把迪迪莫斯或它的卫星
There's no way we can move
didymos or its moon
移♥动♥到足以给地球造成问题的任何程度
in any way big enough to cause
a problem for the earth.
这颗脏脏的卫星小行星
Narrator: The diddy-moon
asteroid weighs
重约105亿磅
around 10 1/2 billion pounds.
那么，如何才能将这么大的一块石头
So how do you knock such
a large lump of rock
从路径上移开呢？
off its path?
♪
我们要发射一艘宇宙飞船
narrator:
We're sending a spacecraft
把这颗脏卫星撞飞
to knock the diddy-moon
asteroid off course.
这颗小行星的移♥动♥速度超过每小时36000英里(约58000公里)
The asteroid is moving at
over 36,000 miles an hour
距离地球约700万英里（约1100万公里）
and is around
seven million miles away.
那么如何移♥动♥一块重达105亿磅的
So how do you move
a 10 and a half billion pound
太空石头呢？
space rock?
你需要非常用力地撞击它才能改变它的轨道
You need to hit it really hard
to change its orbit,
所以将会以超高的速度进入
so it's going to be coming in
at a super high velocity
为了给它传递一束能量动量
in order to impart a bunch
of energy momentum to that moon.
Dart 将以每小时
Narrator:
Dart will hit the target
14000英里（约22500公里）的速度击中目标
at around 14,000 miles an hour.
Dart 撞击的速度
The speed of the dart impact
will be more than nine times
是 ak-47 步♥枪♥子弹的九倍多
the speed of the rifle bullet
from an ak-47.
撞击会给小行星一个小推力
Narrator: The impact will give
the asteroid a small push.
为了计算出推力的大小
To work out how big a push,
我们用艾姆斯垂直炮测试了撞击
we test impacts
with the ames vertical gun.
杜尔达:在加州的美国宇航局艾姆斯研究中心
Durda: At the nasa ames
research center in california,
有一个非常特殊的设施
there's a very special
facility called
叫做艾姆斯垂直射击场
the ames vertical gun range.
这是一种超高速气♥枪♥，能让我们
It's a hyper velocity gas gun
that allows us
以13000到14000英里每小时的速度
to shoot little metal bbs
at rock targets at speeds
向岩石目标发射小型金属弹
up to like 13,000, 14,000
miles per hour.
气♥枪♥能够复♥制♥ dart 任务
Narrator: The gun replicates
the impact
所产生的冲击
the dart mission will make.
它揭示了撞击会以极高的速度
It reveals that an impact
will blow off
撞出少量的碎片
a small amount of debris
but at extremely high speed,
足以给小行星一次额外的推力
enough to give the asteroid
an additional kick.
撞击会把小行星的碎片吹掉
The impact will blow off pieces
of the asteroid,
所以这些碎片会从背面抛出去
so the pieces
are thrown off the back.
这个过程就像一个小火箭引擎
And so that that process acts
like a little rocket engine.
这提供了一个额外的动量变化
That provides an additional
momentum change,
动量推动到目标本身
momentum push
to the target itself.
动能撞击器和喷射出的碎片
Narrator: The combined push
from the kinetic impactor
所产生的合力很小
and the ejected debris is tiny,
约为每小时0.0009英里（1.448米）
around 0.0009 of
a mile per hour.
但希望这足以改变小行星的轨道
But hopefully it's enough
to change the asteroid's orbit.
如果 dart 有效，到时候我们就可以
If dart works, we could
then use a similar mission
用类似的方法来保卫地球
to defend earth
when the time comes.
这可不是我们正在进行练习的
This isn't some
small rock prototype
小岩石的原型
that we're doing this test on.
这是对一颗可能摧毁城市
This is a real dress rehearsal
for an asteroid
甚至可能使地球陷入混乱的小行星的
that could destroy cities
一次真正的彩排
or even maybe send
the earth in chaos.
卫星是一块坚实的岩石
Narrator: The moon of didymos
is a solid lump of rock.
像 dart 这样的动能撞击器
Will a kinetic impactor
like dart work
能对付阿波菲斯这样的碎石堆小行星吗？
with a rubble pile asteroid
like apophis?
当你用弹丸射击碎石堆时
When you shoot a rubble pile
with a projectile,
这有点像试图打沙袋
it's a little bit more
like trying to punch a sandbag.
更多的能量仅仅被
You get a lot more a lot more
the energy is absorbed
移♥动♥袋子里的沙子吸收
into just moving the sand
around inside the bag
而不是将其弹出，因此用这种方法
than ejecting it,
and so rubble piles
移♥动♥碎石堆可能会有点困难
might be a little harder
to move by this method.
我们不知道我们能否使像阿波菲斯这样的碎石堆小行星
Narrator: We don't know if we
can deflect a rubble pile
偏离轨道
asteroid like apophis.
它们仍然是一个明确而现实的危险
They remain a clear
and present danger.
我们可能会生存不下去
And something
we might not survive.
但可能会有一艘太空救生艇
But there may be
a space lifeboat.
2018年，科学家们重新检查了阿波罗14号♥宇航员
In 2018, scientists reexamined
rocks collected by apollo 14
从月球上收集的岩石
astronauts from the moon.
♪
埋在样本里的是一块不应该在那里的石头
buried in the samples was a rock
that shouldn't be there.
他们得到了意想不到的东西
They got something
they didn't expect,
那就是一块地石
and that was an earth rock.
但他们实际上是从月球上表面上捡到的一块石头
They actually picked up
a rock from earth on the moon.
他们没有随身携带
They didn't bring it with them.
很有可能是什么东西撞到地球时
It's very likely that it was
something that was lofted up
被抛了起来，扔出了一堆石头
when something hit earth,
throw up a bunch of rocks.
一些岩石落到了月球上
Some of those rocks
fell on to the moon,
这是月球上的陨石
and that's a meteorite
on the moon,
但它来自地球
but it's from earth.
超级计算机模拟了 k-pg 小行星的撞击
Narrator: Super computer
simulations of
揭示了撞击产生的巨大能量
the kpg asteroid strike revealed
how the impact had so much
是如何将岩石弹射出地球大气层
energy that it catapulted rocks
out of earth's atmosphere
并送入太空
and into space.
然后它们被月球的重力吸引
They were then caught
by the moon's gravity