行星（2019）

had once been ripe for the emergence of life.
我们无法确切知道火星上是否出现过生命 或这些生命是否仍然存在
We won't know for sure whether life began or even perhaps still exists
除非前往火星并找到实物证据
on Mars until we go there and find physical evidence -
微生物或许就深埋于液态水绿洲的土壤之中
so, microbes buried deep below the soil in oases of liquid water,
或者会存在微生物化石 但我们知道
or maybe microbe fossils - but what we do know is that,
35亿年前 地球开始出现生命时
when life began here on Earth, 3.8 billion years ago,
火星的条件与地球非常相似
the conditions on Mars were very similar.
火星上也有海洋 有火山活动
There were seas, there was volcanic activity,
甚至火星上的海底也存在深海热泉
there were even hydrothermal vent systems on the floors of its oceans.
至少有可能的是 地球并不是太阳系
So, it is at least possible that Earth is not the only world
唯一有生命开始的星球
in the solar system where life began.
火星在诺亚时代
The habitable conditions during what's known
出现的宜居条件持续了数亿年
as Mars' Noachian era persisted for hundreds of millions of years.
但红色星球的生命发展前景突然改变
But then, prospects for life on the Red Planet changed dramatically.
在大约35亿年前 诺亚时代结束
Around 3.5 billion years ago, the Noachian era drew to a close
火星进入了更寒冷和干旱的时期 即赫斯伯利亚纪时期
and Mars entered a more frozen, arid phase, known as the Hesperian.
曾经在诺亚时代 在火星表面自♥由♥流动的水
The water that flowed freely over the surface during the age of Noah
被封锁在了巨大的冰库里
became locked away in giant reservoirs of ice.
但是就在这个时期 火星的火山活动更加活跃
But, around the same time, Mars became more volcanically active,
火山爆发和地下熔岩流
and the volcanic eruptions and sub-surface lava flows
偶尔会融化冰层 导致灾难性的洪水
occasionally melted the ice, leading to catastrophic flooding.
这一定是太阳系中
They must have been some of the most spectacular sights
当时最为壮观的景象
in the history of the solar system.
火星 35亿年前
当熔岩向上推动地壳
As molten rock pushed upwards through the crust,
融化的冰水涌向火星表面
meltwater poured out onto the surface.
洪水从南部的高地肆虐而下
It raged down from the southern highlands...
一直来到一个被称为艾彻斯深谷的地方
..until, in a place known as Echus Casma, it plunged
它从4000米高的悬崖俯冲而下
over cliffs 4km high...
这形成了太阳系史上
..creating the largest waterfall
最大的瀑布
the solar system has ever seen.
艾彻斯深谷绝不同于地球上的任何瀑布
Echus Casma would have been like no waterfall ever seen on Earth.
35万立方公里的水流过这里
350 cubic kilometres of water flowed over it.
就像一个长宽高均为70公里的立方体
That's like a cube 70km by 70km by 70km.
所有的水流到宽10公里
It all entered into a canyon 10km wide
长100公里的山谷里 而这一切就发生在几周内
and 100km long, and that happened in a few weeks.
一旦洪水平息 水就消失了
Once the flood subsided, the water disappeared...
火星表面只留下了洪水侵蚀的痕迹
..leaving the evidence of the falls etched into the face of the planet.
艾彻斯深谷
我们不知道火星为何会从温暖潮湿的气候
We don't know precisely why the climate of Mars changed
转变成寒冷干旱的气候
from warm and wet to cold and arid.
我们讨论的是35亿年前
We're talking about events that happened
发生在数亿公里外的一颗行星上的事件
three and a half billion years ago on a planet hundreds of millions
这是一个很难的课题
of kilometres away, so it is a hard problem.
但我们强烈怀疑 火星表面
But we do strongly suspect that changes happening
之所以会发生变化
on the planet's surface were driven
至少有一部分原因来自于火星内部的变化
at least in part by changes in the planet's interior.
火星的核心深处发生的一些变化
Deep within Mars' core,
很可能导致了这颗行星的死亡
something was causing the planet to die...
我们可以从火星的大气层中找到证据
..and the evidence can be found in Mars' atmosphere.
倒计时 10 9 8 7 6
T-minus ten, nine, eight, seven, six,
5 4 3 five, four, three,
火星大气与挥发物演化任务
2 1 two, one.
主发动机开始启动 点火 搭载“火星大气与挥发物演化”探测器的
Main engine start, ignition, and lift-off
阿特拉斯-5型运载火箭发射
of the Atlas V with MAVEN,
执行任务 在火星的大气层
looking for clues about the evolution of Mars
寻找火星演变的线索
through its atmosphere.
2014年9月 美国国家航♥空♥航♥天♥局的“火星大气与挥发物演化”探测器
In September 2014, NASA'S MAVEN probe made its final
最后一次靠近火星
approach to the Red Planet.
它的任务是调查火星
Its mission - to understand what drove the planet's
气候变化的原因
dramatic climate change.
“火星大气与挥发物演化”探测器配备有一系列仪器
MAVEN is equipped with an array of instruments designed to measure
可分♥析♥火星大气中原子和分子的变化
the behaviour of the atoms and molecules in Mars' atmosphere.
探测器沿着一个椭圆轨道绕火星飞行
The spacecraft circles Mars in an elliptical orbit...
它的任务是全面了解
..allowing it to measure the full profile
火星外层大气的状况
of the planet's upper atmosphere.
它的最低点
At its lowest point,
距离火星表面仅150公里
it's just 150km above the surface.
最高点则会超过6000公里
At its highest, a little over 6,000 kilometres.
“火星大气与挥发物演化”探测器在火星大气层的最顶端
And it was at the very top of Mars' atmosphere that MAVEN found
发现了火星发生变化的原因
the key to the mystery of what happened to Mars.
详细的测量分♥析♥表明
Detailed measurements revealed gas is being lost
火星大气中的气体正在消失
from the Martian atmosphere,
以大约
escaping to space
每秒两千克的速度散失到太空中
at a rate of about two kilograms every second.
人们认为在漫长的时间里 火星大气的逐渐散失
Over time, it's thought this gradual stripping away of Mars' atmosphere
致使围绕火星的绝缘层慢慢变薄
has slowly thinned the insulating layer surrounding the planet...
最终导致了火星表面温度的急剧下降
..causing surface temperatures to plummet.
然而是什么原因导致火星大气消失
But what was it that caused Mars to lose its atmosphere
而地球的大气会稳定存在呢
while Earth clung on to hers?
在距离这里1.5亿公里的地方 就是我们看到的落日
150 million kilometres away in that direction is the setting sun,
这是一个巨大的核聚变反应堆
a giant nuclear fusion reactor.
可容纳100万个地球
You can fit one million Earths inside it.
它的表面温度
Now, the surface temperature
约为6000摄氏度
is only around 6,000 degrees Celsius,
但太阳大气 也就是日冕的温度
but the sun's atmosphere, known as its corona,
可达100万摄氏度
is at one million degrees.
这意味着它以所谓的等离子体形式存在
And that means it's in the form of what's known as a plasma, a soup
一种带电粒子的混合物
of electrically charged particles.
如今一些粒子快速移♥动♥ 以太阳风的形式
Some of those particles are moving around so fast that they can escape,
从太阳表面逃逸
and they stream away in what's known as the solar wind.
它们会以每秒几百公里的惊人速度到达地球
They reach the Earth travelling at a few hundred kilometres per second.
如果不加以保护 它们就会吹走我们的大气
And, if we weren't protected, they would strip away our atmosphere.
当太阳落到地平线以下时
And when the sun dips below the horizon...
具备保护性的力场有时会在夜空中出现
..there are times when that protective force field is revealed.
看那边
Just look at that!
那就是美丽的极光
I mean, there is the aurora.
这是大自然的杰作 它们呈现于天空之上
It's the laws of nature, all of them, written across the sky.
来自恒星内部核聚变反应堆的带电粒子
Electrically-charged particles have been driven away from the sun,
从太阳的表面逃逸
ultimately from nuclear fusion reactions in the core of a star.
它们穿过太阳系 撞击地球磁场
They're crossing the solar system, hitting the Earth's magnetic field,
将地球磁场延伸至地球的阴暗面
stretching it out on the dark side of the planet.
然后磁场像橡皮筋一样弹回来
The field then snaps back like an elastic band,
使所有带电粒子沿着两极的磁场线
accelerating all of those charged particles up and down
上下加速 就在这里 在冰岛的上空
the field lines to the poles, which is here in the skies
当带电粒子撞击大气中的
over Iceland, and they hit nitrogen
氮气和氧原子时
and oxygen molecules in the atmosphere.
你将看到量子力学的产生 它们使原子兴奋
And you're seeing quantum mechanics - they're exciting the
使原子发出带有特殊颜色的光
molecules so that they emit light in characteristic colours.
这是我们看到地球磁场的
And, if you think about it, this is the only time
唯一机会
that we really see the Earth's magnetic field.
这是地球生命
It's one of the reasons why life on Earth
得以延续40亿年的原因之一
has been able to persist for four billion years.
所以在某种意义上 这也是我们存在的原因
In a sense, that's the reason that you exist.
地球磁场保护了地球大气
It's Earth's magnetic field that protects our atmosphere
不被太阳风破坏
from the ravages of the solar wind,
这种保护盾的形成
and that protective shield has its origins deep
起源于地球的内部深处
in the planet's interior.
在我的脚下几千公里的地方
Thousands of kilometres down below my feet,
你的脚下也是一样 就是地球的外地核
actually below your feet now, is the Earth's outer core,
它是一团沸腾的铁水
which is a seething mass of molten iron.
内部产生的对流能使铁水上升
Convection currents cause the molten iron to rise,
而地球自转使铁水也会跟着旋转
and then the Earth's rotation causes it to spiral around.
此时导电液体的螺旋流动
Now, a spiralling, circling flow
就像一台发电机
of an electrically conducting liquid is a dynamo.
这台发电机能够产生磁场 地球磁场不仅能上升到
A dynamo generates a magnetic field and the Earth's field rises up,
地球表面 同时也存在于外太空
not just to the surface here, but out into space,
对地球形成了保护盾
forming our protective shield.
也就是我们看到的这一切
And that is what you see there.
和地球一样
And just like Earth,
古老的火星也曾拥有隔离太阳的保护盾
ancient Mars was also shielded from the sun.
极光曾在火星的两极跳跃
Aurora once danced above its poles...