What a planet needs to sustain life | Dave Brain

翻译人员: Yangyang Liu 校对人员: Amy Lu

I'm really glad to be here.

我很高兴能在这里。

I'm glad you're here,

很高兴你们也在这里，

because that would be a little weird.

因为这会有点奇怪。

I'm glad we're all here.

我很高兴我们都在这里。

And by "here," I don't mean here.

我说的"这里"，并不是指这里，

Or here.

或者这里，

But here.

而是这里。

I mean Earth.

我指的是地球。

And by "we," I don't mean those of us in this auditorium,

我说的"我们"并不是指 我们坐在会场里的人，

but life,

而是生命，

all life on Earth --

地球上所有的生命。

(Laughter)

（笑声）

from complex to single-celled,

从复杂的生命到单细胞的生命，

from mold to mushrooms

从霉菌到蘑菇，

to flying bears.

到会飞的熊。

(Laughter)

（笑声）

The interesting thing is,

有趣的是，

Earth is the only place we know of that has life --

地球是我们已知的 唯一有生命的地方，

8.7 million species.

870万种生物。

We've looked other places,

我们曾经在其他星球寻找生命，

maybe not as hard as we should or we could,

或许没有尽全力，

but we've looked and haven't found any;

但我们确实没有发现过。

Earth is the only place we know of with life.

地球是我们已知的 唯一有生命的地方，

Is Earth special?

地球很特别吗？

This is a question I've wanted to know the answer to

从我小时候起，

我就一直想要知道这个问题的答案，

since I was a small child,

and I suspect 80 percent of this auditorium

我觉得这个会场里80%的人

has thought the same thing and also wanted to know the answer.

都曾经思考过同样的问题， 并且想要知道答案。

To understand whether there are any planets --

为了知道是否有其他星球

out there in our solar system or beyond --

—在我们太阳系中或是之外的—

that can support life,

能够支持生命的存在，

the first step is to understand what life here requires.

第一步就是要理解生命需要什么。

It turns out, of all of those 8.7 million species,

事实表明， 虽然地球上有着870万种生命，

life only needs three things.

但生命的存在只需要三样东西。

On one side, all life on Earth needs energy.

首先，所有地球上的生命都需要能量。

Complex life like us derives our energy from the sun,

复杂的生命，例如我们， 从太阳那里获得能量。

but life deep underground can get its energy

但是在地底的生命则 通过其他方式，

from things like chemical reactions.

比如化学反应，来获得能量。

There are a number of different energy sources

在所有的星球上，

都有很多能够获得能量的方式。

available on all planets.

On the other side,

另一方面，

all life needs food or nourishment.

所有的生命都需要食物和营养。

And this seems like a tall order, especially if you want a succulent tomato.

这看起来很难满足，尤其是 如果你想吃一个多汁的番茄。

(Laughter)

（笑声）

However, all life on Earth derives its nourishment

但是，地球生命所需的全部营养

from only six chemical elements,

都只基于六种化学元素，

and these elements can be found on any planetary body

这些元素在太阳系中

所有的星体上都可以找到。

in our solar system.

So that leaves the thing in the middle as the tall pole,

中间那幅图中的东西

反而是最难得到的。

the thing that's hardest to achieve.

Not moose, but water.

不是那只鹿，而是水。

(Laughter)

（笑声）

Although moose would be pretty cool.

虽然那只鹿也很酷。

(Laughter)

（笑声）

And not frozen water, and not water in a gaseous state, but liquid water.

并且不是固态，也不是气态的水， 而是液态的水。

This is what life needs to survive, all life.

水是所有生命的前提。

And many solar system bodies don't have liquid water,

很多太阳系的天体上没有液态水，

and so we don't look there.

所以就可以排除了。

Other solar system bodies might have abundant liquid water,

其他的太阳系天体可能有充足的液态水，

even more than Earth,

甚至比地球上还多，

but it's trapped beneath an icy shell,

但是那些水被阻隔在冰盖下面，

and so it's hard to access, it's hard to get to,

因此很难得到并加以利用。

it's hard to even find out if there's any life there.

即使那里有生命，我们也很难找到。

So that leaves a few bodies that we should think about.

所以只需要考虑 剩下的很少几个星球。

So let's make the problem simpler for ourselves.

让我们进一步简化，

Let's think only about liquid water on the surface of a planet.

先只考虑星球表面上 存在液态水的问题。

There are only three bodies to think about in our solar system,

在太阳系中，只有三个星球的表面

with regard to liquid water on the surface of a planet,

可能存在液态水，

and in order of distance from the sun, it's: Venus, Earth and Mars.

按照距离太阳的远近， 他们是：金星、地球、火星。

You want to have an atmosphere for water to be liquid.

你需要一个让水保持液态的大气层，

You have to be very careful with that atmosphere.

需要非常小心这个大气层，

You can't have too much atmosphere, too thick or too warm an atmosphere,

不能太多，不能太厚，不能太热，

because then you end up too hot like Venus,

因为如果太热，像金星一样，

and you can't have liquid water.

就无法保持液态水。

But if you have too little atmosphere and it's too thin and too cold,

但如果大气太少，太薄或太冷，

you end up like Mars, too cold.

结果就像火星，太冷。

So Venus is too hot, Mars is too cold,

所以金星太热，火星太冷，

and Earth is just right.

地球刚刚好。

You can look at these images behind me and you can see automatically

从我身后的图片，你很容易看出

where life can survive in our solar system.

哪个星球能让生命存活。

It's a Goldilocks-type problem,

这是个“金发姑娘问题”，

and it's so simple that a child could understand it.

即使是小孩子也会明白。

However,

但是，

I'd like to remind you of two things

我想提醒你们，

金发姑娘的故事中， 有两件我们不太在意的事，

from the Goldilocks story that we may not think about so often

but that I think are really relevant here.

在这里却非常关键。

Number one:

第一：

if Mama Bear's bowl is too cold

如果金发姑娘走进房间的时候，

when Goldilocks walks into the room,

熊妈妈的碗太凉，

does that mean it's always been too cold?

是否意味着碗会一直很凉呢？

Or could it have been just right at some other time?

会不会某一个时间， 它的温度会变得刚刚好呢？

When Goldilocks walks into the room determines the answer

金发姑娘走进房间的时间，

决定了我们能获得什么样的答案。

that we get in the story.

And the same is true with planets.

对于行星是同样的道理，

They're not static things. They change.

他们不是一成不变的，他们在改变，

They vary. They evolve.

在变化，在发展。

And atmospheres do the same.

大气层也是一样。

So let me give you an example.

我举个例子，

Here's one of my favorite pictures of Mars.

这是我最喜欢的一张火星的照片，

It's not the highest resolution image, it's not the sexiest image,

它的分辨率不算最高， 也不算最漂亮，

it's not the most recent image,

也不是最近的照片，

but it's an image that shows riverbeds cut into the surface of the planet;

但它展示了火星表面的河床。

riverbeds carved by flowing, liquid water;

这些河床是由流动的液态水，

riverbeds that take hundreds or thousands or tens of thousands of years to form.

经过成千上万年的侵蚀所形成。

This can't happen on Mars today.

但如今火星上不会再形成河床了，

The atmosphere of Mars today is too thin and too cold

现在火星的大气层太薄太冷，

for water to be stable as a liquid.

液态水已经无法稳定存在。

This one image tells you that the atmosphere of Mars changed,

这张图显示了火星大气的变化，

and it changed in big ways.

并且是巨大的变化。

And it changed from a state that we would define as habitable,

它从一个我们认为 可居住的状态变化而来，

because the three requirements for life were present long ago.

因为它很久以前呈现出了 那三个生命存活的要素。

Where did that atmosphere go

那个可以维持液态水的 大气层哪去了？

that allowed water to be liquid at the surface?

Well, one idea is it escaped away to space.

一种观点是大气逃逸到了太空，

Atmospheric particles got enough energy to break free

大气粒子获得了脱离星球重力的能量，

from the gravity of the planet,

escaping away to space, never to return.

逃逸到太空，再也无法回来。

And this happens with all bodies with atmospheres.

在所有存在大气层的天体上都会发生。

Comets have tails

彗星的尾巴，

that are incredibly visible reminders of atmospheric escape.

就是大气逃逸的一种直观表现。

But Venus also has an atmosphere that escapes with time,

但金星同样有正在逃逸的大气层，

and Mars and Earth as well.

火星和地球也一样，

It's just a matter of degree and a matter of scale.

只是逃逸的程度和规模的问题。

So we'd like to figure out how much escaped over time

我们希望计算出逃逸的速度，

so we can explain this transition.

以解释这种变迁。

How do atmospheres get their energy for escape?

大气如何获得逃逸的能量？

How do particles get enough energy to escape?

粒子是怎么获得足够能量的？

There are two ways, if we're going to reduce things a little bit.

简而言之有两种方式，

Number one, sunlight.

第一，太阳光。

Light emitted from the sun can be absorbed by atmospheric particles

太阳发出的光可以被大气粒子吸收

and warm the particles.

并被加温。

Yes, I'm dancing, but they --

是的，我在跳舞，但它们…

(Laughter)

（笑声）

Oh my God, not even at my wedding.

天哪，我结婚那天都没跳过舞。

(Laughter)

（笑声）

They get enough energy to escape and break free

通过加温，它们获得了冲破星球重力

from the gravity of the planet just by warming.

以逃逸的足够能量。

A second way they can get energy is from the solar wind.

它们可以获得能量的第二种方式是， 太阳风。

These are particles, mass, material, spit out from the surface of the sun,

太阳表面会发射出例子、质量、材料，

and they go screaming through the solar system

它们以400千米每秒的速度

at 400 kilometers per second,

在太阳系中冲撞，

sometimes faster during solar storms,

有太阳风暴时会更快。

and they go hurtling through interplanetary space

它们在星际空间中，

towards planets and their atmospheres,

朝着行星和大气层飞奔，

and they may provide energy

它们也会为大气粒子 的逃逸提供能量。

for atmospheric particles to escape as well.

This is something that I'm interested in,

我对这个很感兴趣，

because it relates to habitability.

因为这会和可居住相关。

I mentioned that there were two things about the Goldilocks story

我刚才提到金发姑娘故事中

that I wanted to bring to your attention and remind you about,

有两个我们需要关注的问题，

and the second one is a little bit more subtle.

第二个问题会更微妙。

If Papa Bear's bowl is too hot,

如果熊爸爸的碗太烫，

and Mama Bear's bowl is too cold,

而熊妈妈的碗太凉，

shouldn't Baby Bear's bowl be even colder

如果按这个规律，

熊宝宝的碗不是应该更凉吗？

if we're following the trend?

This thing that you've accepted your entire life,

这件你一直没怀疑的事，

when you think about it a little bit more, may not be so simple.

如果仔细一想，可能没那么简单。

And of course, distance of a planet from the sun determines its temperature.

当然， 大气温度取决于行星和太阳的距离，

This has to play into habitability.

这也决定了可居住性。

But maybe there are other things we should be thinking about.

但可能有其他我们需要考虑的事，

Maybe it's the bowls themselves

可能碗本身，

that are also helping to determine the outcome in the story,

也可以决定故事的结局，

what is just right.

这恰恰是事实。

I could talk to you about a lot of different characteristics

我讲一个不太一样的特性，

of these three planets

它可以影响这三个行星的可居住性，

that may influence habitability,

but for selfish reasons related to my own research

但由于我的一点私心， 因为这是我自己的研究，

and the fact that I'm standing up here holding the clicker and you're not --

并且遥控器在我这儿 而不在你们手里，

(Laughter)

（笑声）

I would like to talk for just a minute or two

我想花一两分钟

about magnetic fields.

聊一下磁场。

Earth has one; Venus and Mars do not.

地球有磁场，而金星和火星没有。

Magnetic fields are generated in the deep interior of a planet

磁场是从星球的内部产生，

by electrically conducting churning fluid material

由电荷驱动旋转的流体，

that creates this big old magnetic field that surrounds Earth.

形成了地球周围的 巨大而古老的磁场。

If you have a compass, you know which way north is.

你用指南针可以分辨出哪里是北，

Venus and Mars don't have that.

但金星和火星没有磁场，

If you have a compass on Venus and Mars,

如果你在金星和火星上用指南针，

congratulations, you're lost.

恭喜，你迷路了。

(Laughter)

（笑声）

Does this influence habitability?

这会影响可居住性吗？

Well, how might it?

会怎么影响？

Many scientists think that a magnetic field of a planet

有些科学家认为 行星的磁场为大气层提供保护，

serves as a shield for the atmosphere,

deflecting solar wind particles around the planet

通过力场效应影响带电粒子，

in a bit of a force field-type effect

having to do with electric charge of those particles.

从而改变太阳风粒子的方向。

I like to think of it instead as a salad bar sneeze guard for planets.

我倒喜欢把它比喻成 食品柜台的防喷嚏罩。

(Laughter)

（笑声）

And yes, my colleagues who watch this later will realize

是的，我的同事看到这个后，

this is the first time in the history of our community

会发现这是我们圈里有史以来

that the solar wind has been equated with mucus.

第一次把太阳风等同成喷嚏口水。

(Laughter)

（笑声）

OK, so the effect, then, is that Earth may have been protected

因此，地球可能因为存在磁场，

for billions of years,

because we've had a magnetic field.

而被保护了数十亿年，

Atmosphere hasn't been able to escape.

使得大气层无法逃逸。

Mars, on the other hand, has been unprotected

然而火星没有受到这样的保护，

because of its lack of magnetic field,

因为没有磁场，

and over billions of years,

经历了数十亿年，

maybe enough atmosphere has been stripped away

足够的大气层逃逸出去

to account for a transition from a habitable planet

使得它变成了不可居住的星球，

to the planet that we see today.

就是今天我们看到的样子。

Other scientists think that magnetic fields

其他科学家认为磁场

may act more like the sails on a ship,

更像是船上的帆，

enabling the planet to interact with more energy from the solar wind

让行星可以通过太阳风 获得更多能量，

than the planet would have been able to interact with by itself.

比星球自己产生的更多。

The sails may gather energy from the solar wind.

船帆可能从太阳风中收集能量。

The magnetic field may gather energy from the solar wind

但磁场从太阳风中吸收能量，

that allows even more atmospheric escape to happen.

会让更多的大气逃逸。

It's an idea that has to be tested,

这个想法还有待验证，

but the effect and how it works

但它的影响和原理也是显而易见的。

seems apparent.

That's because we know

因为我们知道，

energy from the solar wind is being deposited into our atmosphere

太阳风中的能量会被存储到 地球的大气中。

here on Earth.

That energy is conducted along magnetic field lines

这些能量随着磁场被导入两极，

down into the polar regions,

resulting in incredibly beautiful aurora.

形成绚丽无比的极光。

If you've ever experienced them, it's magnificent.

如果你体验过，那真是非常壮丽。

We know the energy is getting in.

我们知道能量正在源源不断的进入，

We're trying to measure how many particles are getting out

我们也试着测量有多少粒子跑出去，

and if the magnetic field is influencing this in any way.

以及磁场是不是在影响这个过程。

So I've posed a problem for you here,

所以我刚刚抛给各位一个问题，

but I don't have a solution yet.

但我还没有答案，

We don't have a solution.

我们没有答案，

But we're working on it. How are we working on it?

但我们正在努力。 我们怎么做的呢？

Well, we've sent spacecraft to all three planets.

我们往三颗行星都发射了航天器。

Some of them are orbiting now,

有些已经在轨运行了，

including the MAVEN spacecraft which is currently orbiting Mars,

包括正围绕火星运行的 MAVEN 航天器，

which I'm involved with and which is led here,

这个项目由这里的 科罗拉多大学主导，

out of the University of Colorado.

我也参与了这个项目。

It's designed to measure atmospheric escape.

它被设计用来观测大气逃逸，

We have similar measurements from Venus and Earth.

在金星和地球， 我们也有类似的测量项目。

Once we have all our measurements,

一旦我们完成测量，

we can combine all these together, and we can understand

综合分析这些数据，我们就可以了解

how all three planets interact with their space environment,

这三颗行星是如何与他们的太空环境

with the surroundings.

以及自身周围的环境相互作用。

And we can decide whether magnetic fields are important for habitability

我们也可以清楚， 磁场对可居住性是否关键。

or not.

Once we have that answer, why should you care?

一旦我们有了答案， 你们为什么会在意？

I mean, I care deeply ...

我是说，我很在意…

And financially as well, but deeply.

财务上很在意，但也确实很在意…

(Laughter)

（笑声）

First of all, an answer to this question

首先，这个问题的答案

will teach us more about these three planets,

会告诉我们更多关于 这三颗行星的事情，

Venus, Earth and Mars,

金星、地球、火星，

not only about how they interact with their environment today,

不只是它们今天如何与 周边环境互相作用，

but how they were billions of years ago,

更多是几十亿年前的情形，

whether they were habitable long ago or not.

很久以前它们是否是可居住的。

It will teach us about atmospheres

它会告诉更多关于围绕着我们、

that surround us and that are close.

与我们息息相关的大气层的事情。

But moreover, what we learn from these planets

此外，从这些行星身上学到的经验，

can be applied to atmospheres everywhere,

可以用在其他任何星球的大气层。

including planets that we're now observing around other stars.

包括我们正在观测的 其他恒星系的行星，

For example, the Kepler spacecraft,

比如，建造并管理于博尔德的 开普勒望远镜，

which is built and controlled here in Boulder,

has been observing a postage stamp-sized region of the sky

近几年一直在观测

一块邮票大小的天空区域，

for a couple years now,

and it's found thousands of planets --

它已经发现了几千颗行星，

in one postage stamp-sized region of the sky

仅仅在一块邮票大小的天空，

that we don't think is any different from any other part of the sky.

和别的区域并没有什么不同。

We've gone, in 20 years,

在这20年里，

from knowing of zero planets outside of our solar system,

我们从对太阳系外的行星一无所知，

to now having so many,

到目前我们知道这么多，

that we don't know which ones to investigate first.

以至于我们不知道该从哪一个下手。

Any lever will help.

每一条线索都很重要。

In fact, based on observations that Kepler's taken

事实上，从开普勒的观测

and other similar observations,

以及其他类似的观测中，

we now believe that,

我们目前相信，

of the 200 billion stars in the Milky Way galaxy alone,

仅在银河系的2000亿颗恒星中，

on average, every star has at least one planet.

通常每颗恒星都至少有一颗行星。

In addition to that,

除此之外，

estimates suggest there are somewhere between 40 billion and 100 billion

这些行星中， 据估算有400亿至1000亿颗

of those planets that we would define as habitable

可以被定义为可居住的，

in just our galaxy.

这仅仅是在我们的银河系。

We have the observations of those planets,

我们在观察这些行星，

but we just don't know which ones are habitable yet.

但我们还不知道哪些是适合居住的。

It's a little bit like being trapped on a red spot --

就像被困在这个红点上一样，

(Laughter)

（笑声）

on a stage

在台上，

and knowing that there are other worlds out there

并且知道这外面有其他的世界，

and desperately wanting to know more about them,

拼命想要了解它们，

wanting to interrogate them and find out if maybe just one or two of them

想调查并找到是否有那么一两个

are a little bit like you.

和你有点像。

You can't do that. You can't go there, not yet.

但你做不到， 你还无法到达那里。

And so you have to use the tools that you've developed around you

所以你只能用你身边的工具，

for Venus, Earth and Mars,

金星，地球，火星，

and you have to apply them to these other situations,

用他们来推演其他的情况，

and hope that you're making reasonable inferences from the data,

并祈祷你正在做有意义的尝试，

and that you're going to be able to determine the best candidates

你将可以做出最佳的判断，

for habitable planets, and those that are not.

关于哪些星球可居住，哪些不可以。

In the end, and for now, at least,

最终，至少是目前，

this is our red spot, right here.

这是我们的红点，就在这里。

This is the only planet that we know of that's habitable,

这是我们唯一知道的宜居的星球，

although very soon we may come to know of more.

虽然可能很快就会发现还有其他的。

But for now, this is the only habitable planet,

但目前，这是唯一宜居的星球，

and this is our red spot.

这是我们的红点。

I'm really glad we're here.

我很高兴我们在这里。

Thanks.

谢谢。

(Applause)

（掌声）