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行星存在生命的要素

What a planet needs to sustain life | Dave Brain

我很高兴能在这里
I’m really glad to be here.
很高兴你们也在
I’m glad you’re here,
因为这会有点奇怪
because that would be a little weird.
我很高兴我们都在这里
I’m glad we’re all here.
我说的”这里” 并不是指这里
And by “here,” I don’t mean here.
或者这里
Or here.
而是这里
But here.
我指的是地球
I mean Earth.
而“我们” 也并非是指 会场里的人
And by “we,” I don’t mean those of us in this auditorium,
而是生命
but life,
地球上所有的生命
all life on Earth —
[笑声]
[Laughter]
从复杂生命体到单细胞
from complex to single-celled,
从霉菌到蘑菇
from mold to mushrooms
到会飞的熊
to flying bears.
[笑声]
[笑声]
有趣的是
The interesting thing is,
地球是已知唯一有生命之处
Earth is the only place we know of that has life —
870万种生物
8.7 million species.
我们曾经找过其它地方
We’ve looked other places,
或许未尽全力
maybe not as hard as we should or we could,
但我们确实没有发现
but we’ve looked and haven’t found any;
地球是已知唯一有生命之处
Earth is the only place we know of with life.
地球很特别吗?
Is Earth special?
从小时候起 我就一直想要知道这个问题的答案
This is a question I’ve wanted to know the answer to since I was a small child,
我想会场里80%的人
and I suspect 80 percent of this auditorium
都有过相同疑问 并都想知道答案
has thought the same thing and also wanted to know the answer.
为了知道是否有其他星球
To understand whether there are any planets —
在太阳系之中或之外
out there in our solar system or beyond —
能够支持生命存在
that can support life,
首先需要理解生命需要什么
the first step is to understand what life here requires.
事实表明 虽然地球上有着870万种生命
It turns out, of all of those 8.7 million species,
但生命存在只需三个条件
life only needs three things.
首先 所有地球上的生命都需要能量
On one side, all life on Earth needs energy.
复杂生命体 例如我们 从太阳那里获得能量
Complex life like us derives our energy from the sun,
但地底生命则通过其它方式
but life deep underground can get its energy
比如 化学反应
from things like chemical reactions.
所有的星球 都有很多获得能量的方式
There are a number of different energy sources available on all planets.
另一方面
On the other side,
所有的生命都需要食物和营养
all life needs food or nourishment.
这看似难以满足 尤其是 如果你想吃个多汁番茄的话
And this seems like a tall order, especially if you want a succulent tomato.
[笑声]
[Laughter]
但是 地球生命所需的全部营养
However, all life on Earth derives its nourishment
都只基于六种化学元素
from only six chemical elements,
这些元素在太阳系中
and these elements can be found on any planetary body
所有星球都可能找到
in our solar system.
中间那幅图中的东西
So that leaves the thing in the middle as the tall pole,
反而是最难得到的
the thing that’s hardest to achieve.
不是那只鹿 而是水
Not moose, but water.
[笑声]
[Laughter]
虽然那只鹿也很酷
Although moose would be pretty cool.
[笑声]
[Laughter]
并且不是固态 也不是气态 而是液态水
And not frozen water, and not water in a gaseous state, but liquid water.
水是所有生命的前提
This is what life needs to survive, all life.
很多太阳系的天体上没有液态水
And many solar system bodies don’t have liquid water,
所以就可以排除了
and so we don’t look there.
其它太阳系天体可能液态水充足
Other solar system bodies might have abundant liquid water,
甚至多于地球
even more than Earth,
但被阻隔在冰盖下面
but it’s trapped beneath an icy shell,
就会难以得到并加以利用
and so it’s hard to access, it’s hard to get to,
即使那里有生命 我们也很难找到
it’s hard to even find out if there’s any life there.
所以只需考虑 剩下很少几个星球
So that leaves a few bodies that we should think about.
让我们进一步简化
So let’s make the problem simpler for ourselves.
先只考虑星球表面 存在液态水的问题
Let’s think only about liquid water on the surface of a planet.
在太阳系中 只有三个星球的表面
There are only three bodies to think about in our solar system,
可能存在液态水
with regard to liquid water on the surface of a planet,
按照距离太阳的远近 它们是:金星、地球、火星
and in order of distance from the sun, it’s: Venus, Earth and Mars.
你需要一个让水保持液态的大气层
You want to have an atmosphere for water to be liquid.
需要非常小心这个大气层
You have to be very careful with that atmosphere.
不能太多 不能太厚 不能太热
You can’t have too much atmosphere, too thick or too warm an atmosphere,
因为如果太热 像金星一样
because then you end up too hot like Venus,
就无法保持液态水
and you can’t have liquid water.
但如果大气太少 太薄或太冷
But if you have too little atmosphere and it’s too thin and too cold,
结果就像火星 太冷
you end up like Mars, too cold.
所以金星太热 火星太冷
So Venus is too hot, Mars is too cold,
地球刚刚好
and Earth is just right.
从我身后的图片 你很容易看出
You can look at these images behind me and you can see automatically
哪个星球能让生命存活
where life can survive in our solar system.
这是个“金发姑娘问题”
It’s a Goldilocks-type problem,
简单到小孩子也能明白
and it’s so simple that a child could understand it.
然而
However,
我想提醒你们
I’d like to remind you of two things
金发姑娘的故事中 有两件我们不太注意的事
from the Goldilocks story that we may not think about so often
在这里却非常关键
but that I think are really relevant here.
第一:
Number one:
如果金发姑娘走进房间的时候
if Mama Bear’s bowl is too cold
熊妈妈的碗太凉
when Goldilocks walks into the room,
是否意味着碗会一直很凉呢?
does that mean it’s always been too cold?
会不会某一时刻 它的温度会变得刚刚好呢?
Or could it have been just right at some other time?
金发姑娘走进房间的时间
When Goldilocks walks into the room determines the answer
决定了我们能获得什么样的答案
that we get in the story.
对于行星是同样的道理
And the same is true with planets.
他们不是一成不变的 他们在改变
They’re not static things. They change.
在变化 在发展
They vary. They evolve.
大气层也是一样
And atmospheres do the same.
我举个例子
So let me give you an example.
这是我最喜欢的一张火星的照片
Here’s one of my favorite pictures of Mars.
它的分辨率不算最高 也不算最漂亮
It’s not the highest resolution image, it’s not the sexiest image,
也不是最近的照片
it’s not the most recent image,
但它展示了火星表面的河床
but it’s an image that shows riverbeds cut into the surface of the planet;
这些河床是由流动的液态水
riverbeds carved by flowing, liquid water;
经过成千上万年的侵蚀所形成
riverbeds that take hundreds or thousands or tens of thousands of years to form.
但如今火星上不会再形成河床了
This can’t happen on Mars today.
现在火星的大气层太薄太冷
The atmosphere of Mars today is too thin and too cold
液态水已经无法稳定存在
for water to be stable as a liquid.
这张图显示了火星大气的变化
This one image tells you that the atmosphere of Mars changed,
并且是巨大的变化
and it changed in big ways.
它从一个我们认为 可居住的状态变化而来
And it changed from a state that we would define as habitable,
因为它很久以前呈现出了 那三个生命存活的要素
because the three requirements for life were present long ago.
那个能维持液态水的大气层哪去了?
Where did that atmosphere go that allowed water to be liquid at the surface?
一种观点是大气逃逸到了太空
Well, one idea is it escaped away to space.
大气粒子获得了脱离星球重力的能量
Atmospheric particles got enough energy to break free
逃逸到太空 再也无法回来
from the gravity of the planet,
逃逸到太空 再也无法回来
escaping away to space, never to return.
在所有存在大气层的天体上都会发生。
And this happens with all bodies with atmospheres.
彗星的尾巴
Comets have tails
就是大气逃逸的一种直观表现
that are incredibly visible reminders of atmospheric escape.
但金星同样有正在逃逸的大气层
But Venus also has an atmosphere that escapes with time,
火星和地球也一样
and Mars and Earth as well.
只是逃逸的程度和规模的问题
It’s just a matter of degree and a matter of scale.
我们希望计算出逃逸的速度
So we’d like to figure out how much escaped over time
以解释这种变迁
so we can explain this transition.
大气如何获得逃逸的能量?
How do atmospheres get their energy for escape?
粒子是怎么获得足够能量的?
How do particles get enough energy to escape?
简而言之有两种方式
There are two ways, if we’re going to reduce things a little bit.
第一 太阳光
Number one, sunlight.
太阳发出的光可以被大气粒子吸收
Light emitted from the sun can be absorbed by atmospheric particles
并被加温
and warm the particles.
是的 我在跳舞 但它们…
Yes, I’m dancing, but they —
[笑声]
[Laughter]
天哪 我结婚那天都没跳过舞
Oh my God, not even at my wedding.
[笑声]
[Laughter]
通过加温 它们获得了冲破星球重力
They get enough energy to escape and break free
以逃逸的足够能量
from the gravity of the planet just by warming.
它们可以获得能量的第二种方式是 太阳风
A second way they can get energy is from the solar wind.
太阳表面会发射出例子、质量、材料
These are particles, mass, material, spit out from the surface of the sun,
它们以400千米每秒的速度
and they go screaming through the solar system
在太阳系中冲撞
at 400 kilometers per second,
有太阳风暴时会更快
sometimes faster during solar storms,
它们在星际空间中
and they go hurtling through interplanetary space
朝着行星和大气层飞奔
towards planets and their atmospheres,
它们也会为大气粒子的逃逸提供能量
and they may provide energy for atmospheric particles to escape as well.
我对这个很感兴趣
This is something that I’m interested in,
因为这会和可居住相关
because it relates to habitability.
我刚才提到金发姑娘故事中
I mentioned that there were two things about the Goldilocks story
有两个我们需要关注的问题
that I wanted to bring to your attention and remind you about,
第二个问题会更微妙
and the second one is a little bit more subtle.
如果熊爸爸的碗太烫
If Papa Bear’s bowl is too hot,
而熊妈妈的碗太凉
and Mama Bear’s bowl is too cold,
如果按这个规律
shouldn’t Baby Bear’s bowl be even colder
熊宝宝的碗不是应该更凉吗?
if we’re following the trend?
这件你一直没怀疑的事
This thing that you’ve accepted your entire life,
如果仔细一想 可能没那么简单
when you think about it a little bit more, may not be so simple.
当然 大气温度取决于行星和太阳的距离
And of course, distance of a planet from the sun determines its temperature.
这也决定了可居住性
This has to play into habitability.
但可能有其他我们需要考虑的事
But maybe there are other things we should be thinking about.
可能碗本身
Maybe it’s the bowls themselves
也可以决定故事的结局
that are also helping to determine the outcome in the story,
这恰恰是事实
what is just right.
我讲一个不太一样的特性
I could talk to you about a lot of different characteristics
它可以影响这三个行星的可居住性
of these three planets that may influence habitability,
但由于我的一点私心 因为这是我自己的研究
but for selfish reasons related to my own research
并且遥控器在我这 而不在你们手里
and the fact that I’m standing up here holding the clicker and you’re not —
[笑声]
[Laughter]
我想花一两分钟
I would like to talk for just a minute or two
聊一下磁场
about magnetic fields.
地球有磁场 而金星和火星没有
Earth has one; Venus and Mars do not.
磁场是从星球的内部产生
Magnetic fields are generated in the deep interior of a planet
由电荷驱动旋转的流体
by electrically conducting churning fluid material
形成了地球周围的 巨大而古老的磁场
that creates this big old magnetic field that surrounds Earth.
你用指南针可以分辨出哪里是北
If you have a compass, you know which way north is.
但金星和火星没有磁场
Venus and Mars don’t have that.
如果你在金星和火星上用指南针
If you have a compass on Venus and Mars,
恭喜 你迷路了
congratulations, you’re lost.
[笑声]
[Laughter]
这会影响宜居性吗?
Does this influence habitability?
会怎么影响?
Well, how might it?
有些科学家认为 行星的磁场为大气层提供保护
Many scientists think that a magnetic field of a planet
通过力场效应影响带电粒子
serves as a shield for the atmosphere,
通过力场效应影响带电粒子
deflecting solar wind particles around the planet
从而改变太阳风粒子的方向
in a bit of a force field-type effect
从而改变太阳风粒子的方向
having to do with electric charge of those particles.
我倒喜欢把它比喻成 食品柜台的防喷嚏罩
I like to think of it instead as a salad bar sneeze guard for planets.
[笑声]
[Laughter]
是的 我的同事看到这个后
And yes, my colleagues who watch this later will realize
会发现这是我们圈里有史以来
this is the first time in the history of our community
第一次把太阳风等同成喷嚏口水
that the solar wind has been equated with mucus.
[笑声]
[Laughter]
因此 地球可能因为存在磁场
OK, so the effect, then, is that Earth may have been protected
而被保护了数十亿年
for billions of years,
使得大气层无法逃逸
because we’ve had a magnetic field.
使得大气层无法逃逸
Atmosphere hasn’t been able to escape.
然而火星没有受到这样的保护
Mars, on the other hand, has been unprotected
因为没有磁场
because of its lack of magnetic field,
经历了数十亿年
and over billions of years,
足够的大气层逃逸出去
maybe enough atmosphere has been stripped away
使得它变成了不可居住的星球
to account for a transition from a habitable planet
就是今天我们看到的样子
to the planet that we see today.
其他科学家认为磁场
Other scientists think that magnetic fields
更像是船上的帆
may act more like the sails on a ship,
让行星可以通过太阳风 获得更多能量
enabling the planet to interact with more energy from the solar wind
比星球自己产生的更多
than the planet would have been able to interact with by itself.
船帆可能从太阳风中收集能量
The sails may gather energy from the solar wind.
但磁场从太阳风中吸收能量
The magnetic field may gather energy from the solar wind
会让更多的大气逃逸
that allows even more atmospheric escape to happen.
这个想法还有待验证
It’s an idea that has to be tested,
但它的影响和原理也是显而易见的
but the effect and how it works seems apparent.
因为我们知道
That’s because we know
太阳风中的能量会被存储到地球的大气中
energy from the solar wind is being deposited into our atmosphere here on Earth.
这些能量随着磁场被导入两极
That energy is conducted along magnetic field lines down into the polar regions,
形成绚丽无比的极光
resulting in incredibly beautiful aurora.
如果你体验过 那真是非常壮丽
If you’ve ever experienced them, it’s magnificent.
我们知道能量正在源源不断的进入
We know the energy is getting in.
我们也试着测量有多少粒子跑出去
We’re trying to measure how many particles are getting out
以及磁场是不是在影响这个过程
and if the magnetic field is influencing this in any way.
所以我刚刚抛给各位一个问题
So I’ve posed a problem for you here,
但我还没有答案
but I don’t have a solution yet.
我们没有答案
We don’t have a solution.
但我们正在努力 我们怎么做的呢?
But we’re working on it. How are we working on it?
我们往三颗行星都发射了航天器
Well, we’ve sent spacecraft to all three planets.
有些已经在轨运行了
Some of them are orbiting now,
包括正围绕火星运行的 MAVEN 航天器
including the MAVEN spacecraft which is currently orbiting Mars,
这个项目由这里的 科罗拉多大学主导
which I’m involved with and which is led here,
我也参与了这个项目
out of the University of Colorado.
它被设计用来观测大气逃逸
It’s designed to measure atmospheric escape.
在金星和地球 我们也有类似的测量项目
We have similar measurements from Venus and Earth.
一旦我们完成测量
Once we have all our measurements,
综合分析这些数据 我们就可以了解
we can combine all these together, and we can understand
这三颗行星是如何与他们的太空环境
how all three planets interact with their space environment,
以及自身周围的环境相互作用
with the surroundings.
我们也可以清楚 磁场对可居住性是否关键
And we can decide whether magnetic fields are important for habitability or not.
一旦我们有了答案 你们为什么会在意?
Once we have that answer, why should you care?
我是说 我很在意……
I mean, I care deeply …
财务上很在意 但也确实很在意……
And financially as well, but deeply.
[笑声]
[Laughter]
首先 这个问题的答案
First of all, an answer to this question
会告诉我们更多关于这三颗行星的事情
will teach us more about these three planets,
金星、地球、火星
Venus, Earth and Mars,
不只是它们今天如何与周边环境互相作用
not only about how they interact with their environment today,
更多是几十亿年前的情形
but how they were billions of years ago,
很久以前它们是否是可居住的
whether they were habitable long ago or not.
它会告诉更多关于围绕着我们
It will teach us about atmospheres
与我们息息相关的大气层的事情
that surround us and that are close.
此外 从这些行星身上学到的经验
But moreover, what we learn from these planets
可以用在其他任何星球的大气层
can be applied to atmospheres everywhere,
包括我们正在观测的 其他恒星系的行星
including planets that we’re now observing around other stars.
比如 建造并管理于博尔德的 开普勒望远镜
For example, the Kepler spacecraft, which is built and controlled here in Boulder,
近几年一直在观测
has been observing a postage stamp-sized region of the sky
一块邮票大小的天空区域
for a couple years now,
它已经发现了几千颗行星
and it’s found thousands of planets —
仅仅在一块邮票大小的天空
in one postage stamp-sized region of the sky
和别的区域并没有什么不同
that we don’t think is any different from any other part of the sky.
在这20年里
We’ve gone, in 20 years,
我们从对太阳系外的行星一无所知
from knowing of zero planets outside of our solar system,
到目前我们知道这么多
to now having so many,
以至于我们不知道该从哪一个下手
that we don’t know which ones to investigate first.
每一条线索都很重要
Any lever will help.
事实上 从开普勒的观测
In fact, based on observations that Kepler’s taken
以及其他类似的观测中
and other similar observations,
我们目前相信
we now believe that,
仅在银河系的2000亿颗恒星中
of the 200 billion stars in the Milky Way galaxy alone,
通常每颗恒星都至少有一颗行星
on average, every star has at least one planet.
除此之外
In addition to that,
这些行星中 据估算有400亿至1000亿颗
estimates suggest there are somewhere between 40 billion and 100 billion
可以被定义为可居住的
of those planets that we would define as habitable
这仅仅是在我们的银河系
in just our galaxy.
我们在观察这些行星
We have the observations of those planets,
但我们还不知道哪些是适合居住的
but we just don’t know which ones are habitable yet.
就像被困在这个红点上一样
It’s a little bit like being trapped on a red spot —
[笑声]
[Laughter]
在台上
on a stage
并且知道这外面有其他的世界
and knowing that there are other worlds out there
拼命想要了解它们
and desperately wanting to know more about them,
想调查并找到是否有那么一两个
wanting to interrogate them and find out if maybe just one or two of them
和你有点像
are a little bit like you.
但你做不到 你还无法到达那里
You can’t do that. You can’t go there, not yet.
所以你只能用你身边的工具
And so you have to use the tools that you’ve developed around you
金星 地球 火星
for Venus, Earth and Mars,
用他们来推演其他的情况
and you have to apply them to these other situations,
并祈祷你正在做有意义的尝试
and hope that you’re making reasonable inferences from the data,
你将可以做出最佳的判断
and that you’re going to be able to determine the best candidates
关于哪些星球可居住 哪些不可以
for habitable planets, and those that are not.
最终 至少是目前
In the end, and for now, at least,
这是我们的红点 就在这里
this is our red spot, right here.
这是我们唯一知道的宜居的星球
This is the only planet that we know of that’s habitable,
虽然可能很快就会发现还有其他的
although very soon we may come to know of more.
但目前 这是唯一宜居的星球
But for now, this is the only habitable planet,
这是我们的红点
and this is our red spot.
我很高兴我们在这里
I’m really glad we’re here.
谢谢
Thanks.
[掌声]
[Applause]

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视频概述

“金星太热,火星太冷,地球刚刚好”,行星科学家戴夫·布莱恩说。但是,为什么呢?就在这个关于行星的幽默的演讲中,布莱恩解释了关于行星存在生命的有趣知识,以及为什么人类可以在正确时间,正确地点,出现在有生命星球的时间线上。

听录译者

收集自网络

翻译译者

B11101001

审核员

赖皮

视频来源

https://www.youtube.com/watch?v=9RTkZaX1cH0

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