了解宇宙是如何运行的（2010）

How the Universe Works S05E07

Part 5 April 18, 2021, 7:47 p.m.

由电磁效应又产生了一个
which in turn generates a magnetic field
围绕地球上升的磁场，就像一个磁场屏蔽
that rises up around the earth, acting like a magnetic shield,
保护我们的大气层不受太阳风的破坏
protecting our atmosphere from the ravages of the solar wind.
38亿年前
3.8 billion years ago
火星也有一个熔化了的地核和磁场
Mars had a molten core and a magnetic field.
但有东西让它的护盾消失了
But something caused its shield to drop.
火星小小的熔岩内核是否因为太冷而无法发挥作用？
Did Mars' small molten core simply get too cold to function?
还是有其他原因
Or did something else kickstart
导致了火星生命的第三次大灭绝？
this third great extinction of martian life?
一个新的有争议的理论将部分原因
A new and controversial theory points the finger
归咎于古代北极撞击的影响
partly at the ancient borealis impact.
如此大规模的撞击
A giant impact of this scale
可以影响一系列的温度
can affect a range of temperatures,
从炽热的内核到较冷的外地幔
from the hot inner core to the cooler outer mantle.
45亿年前
4.5 billion years ago
使第一代火星生命蒸发的
the impact that vaporizes
北极撞击大事件
the first generation of martian life
也将热量送入火星
also drives heat into the planet,
增加了外地幔的温度
increasing the temperatures in the outer mantle.
行星内部的热量趋于平衡
The heat inside the planet evens out,
金属慢慢停止搅动
and the metals slowly stop churning.
但由于温度梯度比较小……
But there's less of a temperature gradient ...
使得这个动态过程很难
that makes it harder for this dyno process to,
驱动强磁场
to drive a strong magnetic field.
几亿年后
Over hundreds of millions
火星的磁场关闭了
of years, Mars' magnetic field shuts down.
当火星突然失去了
When Mars lost its magnetic
它的磁场
field all of a sudden
它就非常容易受到太阳风的攻击
it was completely vulnerable to the solar wind.
太阳风可以分解并带走
The solar wind could break apart
火星的大气层
and carry away the martian atmosphere.
37亿年前
3.7 billion years ago
超级强悍的火星生命也同样面临灭绝
super tough martian life faces annihilation.
一点一点地，大气层正被吹进太空
Bit by bits, the atmosphere is being swept into space.
整个星球的气压都在下降
The air pressure is dropping across the planet
火星上的大部分水已经蒸发殆尽
and most of Mars' water has already boiled away.
没有这种珍贵的液体
The chances of survival
存活的机会微乎其微
without this precious liquid are remote.
但是，对于火星生命来说，还有一个更迫在眉睫的危险
But, for the martians, there's an even more immediate danger.
由于没有了磁场和厚厚的大气层
With no magnetic field and no thick atmosphere,
火星表面感受到了太阳辐射的
the surface of Mars feels the full force
全部力量
of the sun's radiation.
如果是地表的
If you're a microbe
微生物
on the surface,
就必须要适应
you would have to make do
很少的大气，没有水的环境
with very little atmosphere, no water,
大量来自太阳的紫外线
this flood of ultraviolet light from the sun,
还有那些一直撞到你身上的粒子
and these particles which are slamming into you all the time.
当火星生命受到
The martians are bombarded
太阳风辐射的轰击后
by radiation from the solar wind.
他们的DNA会被撕裂
It rips their DNA apart.
没有大气层
Without an atmosphere,
这个星球的表面就是无菌的
the surface of the planet is sterilized.
但这真的是火星生命的终结吗？
But is this really the end for martian life?
生命是如此顽强
Life is so tenacious,
即使是那些难以置信的灾难性变化,它也能幸存下来
it can survive even those incredible catastrophic changes,
而且可能今天还在那里
and it may still be there today.
为了在辐射中存活下来
To survive the radiation,
火星生命必须深入地下
martian life would have had to have moved deep underground.
在这个受保护的地下环境中
In this protected subterranean environment
它也可能会找到液态水的来源
it may also have found a source of liquid water,
如果是那样的话
and if that happened,
火星生命今天还会在那里
could the martians still be there today,
等着我们去拜访并打招呼它们吗？
waiting for us to drop in and say hello?
自20世纪60年代以来
Since the 1960s
机器人探测器和着陆器
robotic probes and landers
一直在火星表面寻找生命的迹象
have been searching the surface of Mars for signs of life.
但他们找对地方了吗？
But have they been looking in the right places?
火星表面是一片没有水的沙漠
The surface of Mars is a waterless desert
受到有害辐射的轰炸
that's bombarded by harmful radiation.
如果今天火星上还有第♥四♥代♥生命存在
If a fourth incarnation of martian life is alive today,
许多科学家认为它一定在地下深处
many scientists think it'll have to be deep underground.
在火星表面之下
Underneath the surface of Mars
可能拥有生命所需的一切条件
you may have all the conditions you need for life.
那里可能有一些液态水
There may be some liquid water down there,
而且也不受地表
and you're also protected from the intense radiation
强烈辐射的影响
that you find on the surface.
对于寻找火星生命的
Scientists are split
最佳地点在地下这个观点，科学家们意见不一
on the best underground places to search for martian life.
但如果贾尼·拉德博在火星上
But if jani radebaugh were on Mars,
她就会跑到最近的沙丘上开始挖掘
she would head to the nearest sand dune and start digging.
这里你可以
Here you can see
看到表面以下是潮湿的沙子
this is wet sand just below the surface.
这是一个能够容纳生命的完美环境
This is the perfect environment to be able to house life.
即使是在地球上最干燥的沙漠里
Even in the very driest deserts on earth,
在沙丘中，在沙丘之间
in between the sand dunes, in the inter-dunes,
你也能发现从地下深处
you can find water percolating up from Springs
渗出的泉水，而这就是
that come up from deep under the ground,
生命形成和生长的完美条件
perfect for life to form and grow.
如果你继续挖掘……
And if you just keep on digging...
在沙丘间的底部
Down into the bottom of the inter-dune,
也许你能到碰触到地下水
maybe you would reach the water table.
如果你到达了火星的地下水位
And if you reach the water table on Mars,
你就拥有了适合生命存在的所有条件
now you have all the conditions just right for life.
我打赌，这就是我要去的地方
This is my bet, this is where I'd go,
就在沙丘之间
right between the dunes.
在沙漠中挖掘火星生命
Digging for martian life
是一种选择
in the desert is one option.
但有些科学家有不同的想法
But some scientists have very different ideas,
行星科学家妮娜·兰扎(Nina lanza)
and planetary scientist Nina lanza
需要带一根绳子和一个手电筒来进行搜索
would need to pack a rope and a flashlight for her search.
所以如果要去火星寻找生命
So if were to go to Mars to find life,
我会去熔岩洞
I would go to a lava tube.
熔岩洞
Lava tubes are made
是古代火山形成的
by ancient volcanoes,
是地下熔岩流留下的管道
the empty leftovers from underground lava flows.
如今，它们形成了很深的隧♥道♥
Today, they form deep tunnels,
隔绝了辐射，也隔绝了
shielded from radiation and shut off
火星恶劣气候的影响
from the harsh martian climate.
我们从未进入过
We've never been
火星的熔岩洞
in a lava tube on Mars,
但那里绝对有可能存在液态水
but it is absolutely possible that there's liquid water.
所以，在这样的环境中可能会有一些水分
So, that's an environment where you could have some moisture,
也可能会有一些温度，这里生命可以免受辐射
you could have a little warmth, you're protected from radiation.
我认为火星微生物在那里会很开心
I think that a martian microbe would be very happy there.
在火星上发现生命
Finding life on Mars
将是人类一项不朽的成就
would be a monumental human accomplishment.
但这是有危险的
But there is a danger.
把火星上的生命暴露给地球上的生命
By exposing martian life to life from earth,
我们会不会无意中引发另一场灭绝事件？
could we unwittingly set off yet another extinction event?
人类一直是
Humans have been
地球上最有效的物种灭绝
one of the most effective extinction mechanisms
机制之一
of life on earth.
有趣的问题是
The interesting question will be,
我们会在火星上制♥造♥类似的灾难吗？
will we produce a similar calamity on Mars?
如果有一天人类去了火星
If humans someday go to Mars,
那么我们将成为一个入侵物种
then we will be an invasive species,
如果有一些火星生命
and if there is some martian life
存活在某个生态位上
that's hanging on in some niche,
我们将成为他们最终的毁灭者
we could be their ultimate destroyers.