了解宇宙是如何运行的（2010）

How the Universe Works S01E06

Part 5 April 18, 2021, 7:57 p.m.

保护木星的大气层
and protects Jupiter's atmosphere.
研究木星磁场的科学家
When scientists studied
Jupiter's magnetic field,
发现磁场还会影响木星的卫星
they discovered it was
affecting Jupiter's moons.
满布火山的卫星艾奥
The volcanic moon, lo,
在相距木星217000哩的地方运转
orbits only 217,000
miles from the planet.
艾奥的火山每秒喷发上吨♥的气与尘
lo's volcanoes blast a tonne of gas
and dust into space every second.
经木星磁场不断增压
And Jupiter's magnetic
field supercharges it,
形成强力辐射带
creating powerful belts of radiation.
是以木星附近有不同形式的活动
And that makes the vicinity of Jupiter
very active in many different ways.
要是用无线电天线指向木星
If you point a radio antenna at Jupiter,
你可以收听到各种各样的声息
one can hear all sorts of interactions
是行星与磁场之间互为作用的声息
happening between the planets
and the magnetic field.
这是木星磁场的声音
This is the sound of
Jupiter's magnetic field.
木星与土星不用靠太阳风引发极光
Jupiter and Saturn don't need
the solar wind to make auroras.
它们的强大磁场足以自♥制♥极光
They have huge magnetic
fields that create their own.
钱德拉太空望远镜摄得木星的极光
The Chandra space telescope took
these images of Jupiter's auroras.
而太空总署的探测器卡西尼号♥
And NASA's Cassini probe
则拍下土星极光的美丽影像
took these beautiful
pictures of auroras on Saturn.
这些极光证明气态行星也有磁场
These auroras are proof that gas
planets have magnetic fields, too.
但气态行星如何产生磁场?
But how do gas planets
generate magnetic fields?
地球磁场是超热的液态金属…
On Earth, a super-hot liquid metal
围绕地球的固态铁核心运转而得来
spinning around the planet's
solid-iron core does the job.
气态行星的原理多半大同小异
Gas planets probably do
roughly the same thing.
只是气态巨行星并无高热铁质核心
But gas planets don't
have hot-iron cores.
它们的核心是尘与冰凝结而成
They formed around frozen
cores of dust and ice.
所以核心内的究竟仍然是谜
So exactly what's going on
deep inside is a mystery.
木星的最深处究竟由甚么构成
At the very deepest interior of Jupiter,
我们还是莫测高深
we really don't understand what
composes those deep interior states.
所以木星中心也许是个实心内核
So it could be that the very
centre of Jupiter has a solid core.
又或者真的只有液体
Or it could actually
just be still fluid.
我们也许永远不得而知
We may never find out
不会有探测器能走过这44000哩
No probe could ever make
the 44,000-mile journey
探索行星的中心
to the planet's centre to investigate.
伽利略号♥在远离核心处已给压毁
Galileo was crushed before it got
anywhere near the planet's core.
于是科学家在地球的实验室里
So now scientists are
recreating Jupiter's interior
复♥制♥一个木星核心
right here in a lab on Earth.
加州利弗莫尔的国家点燃设施内
Here at the National Ignition
Facility in Livermore, California,
他们用最强力的激光模拟木星核心
they're simulating Jupiter's core
using the world's most powerful laser.
设施的设计是用来压缩氢气
This facility is really
designed to compress hydrogen
压缩至极高密度与温度
to extreme densities and temperatures.
木星内的巨压
Inside Jupiter, extreme
pressures are created
来自四万哩厚的氢压向核心的重量
by the weight of 40,000 miles of
hydrogen gas crushing down on the core.
在实验室里的方法
In the lab,
则是用192道激光束射向少量的氢
it's done by focusing 192 laser
beams on a tiny sample of hydrogen.
待压力达到地球表面压力一百万倍
As the pressure in the sample reaches over a
million times the surface pressure on Earth,
氢就会转化为液体
the hydrogen turns into a liquid.
待压力达至地球表面压力几千万倍
But when it reaches tens of
millions of times the pressure,
近似木星核心内的程度
more like at Jupiter's core,
氢竟出现奇异变化
something really weird
happens to the hycfrogen.
压力大至能促使氢分子重新排列
The pressure is so great that it
actually re-arranges the hydrogen,
让基本的氢分子变成可以传导
which is a very basic molecule,
until it is able to conduct
于是把42的结构转化为金属形态
So it changes the structure
of H2 into a metallic form.
科学家推断木星内也是如此这般
Scientists think this is
what's happening inside Jupiter:
压力与热力把内核转化为金属氢
pressure and heat have transformed the
planet's core into metallic hydrogen.
木星的金属核心好比地球的铁核心
Jupiter's metallic core works
like the iron core in the Earth.
为这颗气态行星产生巨大的磁场
It generates the gas planet's
gigantic magnetic field.
引力与热力左右行星的演变路向
Gravity and heat shape
how planets evolve,
由内核至外♥围♥大气层都受其影响
from their inner cores to
their outer atmospheres.
二者是创造行星的创作主力
They're the great creative
forces in planet building.
不过还有一种素材能左右行星形貌
But there's another ingredient that has
a lot to do with how planets turn out.
那种素材就是水
And that ingredient is water.
行星看似固定不变
Planets may seem fixed and unchanging,
其实它们不断在变
but they never stop evolving.
我们的太阳系内
In our own solar system,
一颗行星失去大气层后变荒芜废墟
one lost its atmosphere and
became a barren wasteland.
另一颗行星则升温而变地狱世界
Another heated up and
became the planet from he I
地球也有改变
Planet Earth has changed as well
改变的动力是水
and the game changer was water.
由太空回看地球, 无处不是水
When you look at Earth from
space, you see a lot of water.
地球毕竟是个蓝色星球
We are the Blue Planet, after all.
所以一定是湿漉漉的了, 对不对?
So it must be really wet, right?
怎看地球表面有3/4给海洋覆盖
It looks at first glance that our Earth of
course, covered three-quarters by oceans,
一个水头充足的世界
it's a very water-rich world.
事实不然
Not true.
以质量计, 地球只有0.06%是水
The Earth, by mass, is
only 0.06 percent water.
地球表面有水, 就是海洋
There's some water on the
surface in the form of oceans,
地幔里也有水
some water trapped in the mantle.
但其实地球是一团干硬岩石
But actually, the Earth
is a relatively dry rock.
岩质的内行星全都接近太阳
All of the inner rocky planets
formed very close to the sun,
所以诞生之初是干旱之地
so they started off dry.
有水也会蒸发净尽
Any water they might
have had evaporated away
或是在撞击时飞走
or was blown away by impacts.
地球诞生时的撞击实在频繁猛烈
These massive collisions that
formed the Earth were so energetic
所以这里的水早已蒸发
that any water that had been
here would have been vaporised
流出地球
and lost from the Earth,
那么地球今天的水是从何而来?
So where did Earth get all
the new water we have today?
由外地迁来
It moved here.
你在太空远望
When you look farther out
看看木星、土星、天王星与海王星
and you look at Jupiter,
Saturn, Uranus, and Neptune,
那些行星都有大量水分锁在其中
those planets have enormous amounts
of water locked up inside them.
更极端的例子是它们的卫星
And even more
dramatically are the moons.
木星、土星、天王星与海王星
The moons of Jupiter,
Saturn, Uranus, and Neptune
它们的卫星, 成分中过半是水
are at least 50 percent water.
太空之中有许多水
There was a lot of water out there.
太空的水又如何流落地球?
So how did some of it
get to planet Earth?
十之八♥九♥是太阳系更远角落里
And the answer almost certainly is that
left farther out in our solar system
哪里的小行星与彗星
were some asteroids and some comets,
它们远离太阳, 得以保留水分
far enough from the sun that
they could retain their water.