了解宇宙是如何运行的（2010）

How the Universe Works S01E06

Part 3 April 18, 2021, 7:57 p.m.

向太空喷发
blasting out into space.
是为太阳风
It's called the solar wind.
太空里的航♥天♥员看得见太阳风
Astronauts in space can see it.
但要闭上眼睛才得见
But only when they close their eyes.
偶然, 闭上眼睛会看见一点闪光
Occasionally, you see a little
flash with your eyes shut.
那是活跃粒子钻入你头部
And that is an energetic
particle coming through your head
与你眼睛内的液体发生作用
and interacting with the
fluid inside your eye,
形成那点闪光
and it makes a little light flash.
几分钟看见一次
And you see these every
couple of minutes or so,
要是你闭上眼睛又未睡去
that you're awake with your eyes shut.
航♥天♥员接触太阳风过量
If the astronauts were exposed
to a lot more of the solar wind,
可以致命
it could be a killer.
太阳神计划期间
During the Apollo programme,
两次登月任务之间曾爆发太阳风
in between two of the moon missions,
there was an outburst on the sun
当时若有航♥天♥员在太空, 可能送命
that would have killed the
astronauts if they had been there.
太空辐射可不是儿嬉的
So space radiation
is a serious business.
但回到地球, 太阳风并不构成威胁
But here on Earth, the solar
wind isn't much of a threat
因为我们有无形罩保护
because we have an
invisible protective shield,
就是地球核心产生的磁场
a magnetic field generated
by the planet's core.
地球中心是一个固体内核
The very centre of the Earth
is the solid inner core.
是一个坚实的铁晶球
It's a hard, iron, crystalline ball.
外面厚厚一层液态铁不断对流滚动
Then there's a thick layer of liquid
iron, which is convecting churning motions,
由此衍生磁场
which give rise to the magnetic field.
理论是那样说
Well, that's the theory.
为了证实铁质地核能产生磁场
To prove that an iron core
can generate a magnetic shield,
科学家在实验室里自♥制♥行星
scientists built their
own planet in a lab.
这个直径10呎, 重量26吨♥的球体
This 10-foot,
26-tonne sphere
模拟地球深处的环境
simulates conditions
deep inside the Earth.
中心的金属球就是地球的核心
A metal ball in the centre
acts as the planet's inner core.
周围有液态钠以90哩时速运转
Liquid sodium spins around
it at 90 miles an hour,
模仿液态金属围绕地核运转的作用
imitating the effects of molten metal
spinning around the Earth's core.
设计这个实验是要尝试制♥造♥磁场
We built this experiment to try
to generate a magnetic field,
从而了解地球何以有磁场
to attempt to understand why
the Earth has a magnetic field
而别的行星却没有磁场
and why other planets do
not have magnetic fields.
运作起来就像汽车的发电器
It works like the generator in your car,
用盘卷的电线产生电力
where rotating coils of
wire produce electricity.
实验中, 液态钠围绕核心滚动
In the experiment, liquid
sodium churns around the core
产生磁场
and generates a magnetic field.
它与发电机大同小异
it's very much like an
electrical generator.
制♥造♥动力来产生磁场
You have motion that is able
to generate magnetic fields
把能量、动能转化为磁能
by turning the energy, the
motion, into magnetic energy.
地球深处的动态一样
The same thing happens
deep inside the Earth.
地球转动时
As the Earth spins,
液态铁围绕固体核心流动
the hot liquid metal flows
around the solid core,
把能量转化为磁场, 由两极逸出
transforming its energy into a magnetic
field that emerges from the poles.
磁场替地球挡开了太阳风
It protects the planet's
atmosphere from the solar wind.
要是行星有磁场
And if the planet has a magnetic field,
就会把太阳风导走, 绕过行星
that solar wind will be diverted
around the planet by the magnetic field.
磁场让太阳风转向, 偏离地球而去
The magnetic field deflects the
solar wind around the planet,
保护地球的大气层与地球表面万物
protecting the atmosphere and
everything on Earth's surface.
有时太阳辐射风暴与磁场交缠起来
Sometimes big storms of solar radiation
will mix it up with the magnetic field.
就会在两极爆发出灿烂炫目的极光
Then we get big light shows
over the poles, the auroras.
没有磁场
Without a magnetic force field,
太阳风会吹走地球的大气层与水
the solar wind would blast away
Earth's atmosphere and water,
留下一个生机绝灭的行星
leaving a dead, arid planet,
就似火星
a lot like Mars.
火星的形成过程与地球无异
Mars formed just like Earth.
但今天的火星冰冷干涸, 大气稀薄
But today, it's cold and
dry with little atmosphere.
两颗行星何以有那么大的差别?
So why are the two
planets now so different?
2004年
In 2004,
太空总署派出两架火星探测器
NASA sent two robot
explorers to Mars to find out.
探测器名叫精神号♥与机会号♥
The rovers, named
Spirit and Opportunity,
在火星表面探索了许多哩
explored miles of the Martian surface.
证实火星是干涸而难以生存的荒漠
They confirmed that Mars
is a dry and hostile desert,
大气层只及地球的1%
with only one percent
the atmosphere of Earth.
但它们也找到火星曾经有水的遗迹
But they did find evidence
of water in the past.
火星不是自始就是荒漠
Mars was not always a desert.
我们找到有力证据
We have found compelling evidence
证明火星曾经有水
that water was once beneath the surface,
冒出地面后就蒸发无踪
came to the surface,
and evaporated away.
我们在几处地方看见波纹遗迹
We also see in a few
places ripples preserved,
就是水流过沙土留下的纹路
of the sort that are formed
when water flows over sand.
所以不独地下有水, 表面也有水流
So not only did water exist below the
surface, it had flowed across the surface.
要是火星以前有水
If Mars had water once,
多半以前也有厚重的大气层
it probably also had a thick atmosphere.
那么发生了甚么事?
So, what happened?
我们看得出火星曾经有活火山
We can see that Mars
once had active volcanoes.
意味以前也有滚热的地心
So it had a hot interior at some point
因为火星与地球都以同一材料构成
And because it was made
of the same stuff as Earth,
所以也有一个热铁地核
it would have had a hot-iron core,
再由液态铁包围
surrounded by liquid
metal at its centre.
故此火星也该有磁场
So it should have had
a magnetic field too.
问题是: 磁场哪里去了?
The question is, where did it go?
火星形成初期, 似乎具有强力磁场
Early in the planet's history, Mars
apparently had a strong magnetic field.
来由大概与地球的相同
And it was probably caused in
the same way as it is on Earth.
只是火星比地球小
But Mars is a smaller planet than Earth.
是以热力流失得快
It's gonna lose its heat
more rapidly as a consequence.
热力流失, 液态核心就会凝固
And what that means is that
liquid core can freeze solid.
核心凝固, 对流也就终止
Freeze the core solid,
the convection will stop.
对流终止, 磁场也就消失
The convection stops, the
magnetic field goes away.
磁场一去
As the magnetic shield died,
大气层给太阳风刮走, 水分蒸发
the solar wind blasted away the
atmosphere and the water evaporated.
火星顿变冷冰冰的绍地
Mars became a cold, barren planet.
岩质行星火星、地球、金星与水星
Mars, Earth, Venus, and
Mercury, the rocky planets,
全都在太阳1.5亿哩内形成
all formed within 150
million miles of the sin.
但四倍距离之外
But four times farther out,
太阳炮制了另一类行星
the sun baked a very
different kind of planet
这批庞然大物由气体构成
They're gigantic, they're made of gas,
这些巨物完全没有固态表面