What a planet needs to sustain life | Dave Brain

譯者: Regina Chu 審譯者: Marssi Draw

I'm really glad to be here.

我真的很高興能來這裡。

I'm glad you're here,

我也很高興你們能來這裡，

because that would be a little weird.

要不然會有點奇怪。

I'm glad we're all here.

我很高興我們都在這裡。

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

我說的「這裡」，不是現場這裡。

Or here.

或這裡。

But here.

卻是這裡。

I mean Earth.

我指的是地球。

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

而且我說的「我們」， 不是這座大禮堂裡的各位，

but life,

而是生命，

all life on Earth --

地球上所有的生命──

(Laughter)

（笑聲）

from complex to single-celled,

從複合體到單細胞，

from mold to mushrooms

從黴菌到蘑菇，

to flying bears.

到飛天熊都是。

(Laughter)

（笑聲）

The interesting thing is,

有趣的是，

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

地球是我們知道 唯一有生命的地方──

8.7 million species.

八百七十萬種生物。

We've looked other places,

我們找過其它地方，

maybe not as hard as we should or we could,

可能找得還不夠勤快，

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

但是我們找過， 沒有發現任何生物。

Earth is the only place we know of with life.

地球是我們所知唯一有生命的地方。

Is Earth special?

地球得天獨厚嗎？

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

這個問題的答案

我從小時候就想知道，

since I was a small child,

and I suspect 80 percent of this auditorium

而且我猜禮堂裡八成的人

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

都想過同樣的事，也想知道答案。

To understand whether there are any planets --

要知道是否有別的行星──

out there in our solar system or beyond --

無論是在我們的太陽系 還是其它地方──

that can support life,

能支持生命，

the first step is to understand what life here requires.

第一步要了解在這裡 生命的要素是什麼。

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

事實證明， 這八百七十萬種物種

life only needs three things.

只需要三件事就能維持生命。

On one side, all life on Earth needs energy.

那邊那張照片， 地球上所有的生命都要能量，

Complex life like us derives our energy from the sun,

像我們這樣的複合生物體 要從太陽取得能量，

but life deep underground can get its energy

地下深處的生物

則從化學反應取得能量。

from things like chemical reactions.

There are a number of different energy sources

地球上有很多種能量來源

available on all planets.

可供大家使用。

On the other side,

另外那一邊照片，

all life needs food or nourishment.

所有的生命都需要食物或營養。

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

這聽起來像是無理的要求， 尤其在你想要一顆多汁的番茄時。

(Laughter)

（笑聲） （譯註：一般超市的番茄都很乾）

However, all life on Earth derives its nourishment

然而，地球上所有的生命

from only six chemical elements,

只要六種化學元素就能取得營養，

and these elements can be found on any planetary body

而這些元素可在

我們的太陽系中 每一個行星體上找到。

in our solar system.

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

所以這讓中間這項成了高不可及、

the thing that's hardest to achieve.

很難拿到的東西。

Not moose, but water.

不是麋鹿，是水。

(Laughter)

（笑聲）

Although moose would be pretty cool.

雖然麋鹿也滿酷的。

(Laughter)

（笑聲）

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

不是冰凍的水，也不是氣狀的水， 而是液態水。

This is what life needs to survive, all life.

這是生命要生存都需要的東西。 所有的生命。

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

許多太陽系沒有液態水，

and so we don't look there.

所以我們不去那裡找。

Other solar system bodies might have abundant liquid water,

有些太陽系可能有大量液態水，

even more than Earth,

甚至可能多過地球，

but it's trapped beneath an icy shell,

但是都困在冰層底下，

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

所以很難拿到，很難接近，

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

甚至很難發現那裡到底有沒有生命。

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

這樣只剩下幾座星體我們應該考慮。

So let's make the problem simpler for ourselves.

所以我們來為自己簡化一下問題。

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

我們只要想想 在星球表面的液態水就好。

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

這樣我們的太陽系裡 只剩三座星體可想，

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

考慮行星表面是否有液態水，

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

與太陽的距離依次是 金星、地球及火星。

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

你要有大氣層使水能維持液態。

You have to be very careful with that atmosphere.

你必須非常小心考慮大氣層。

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

你不能有太大的大氣層， 太厚或太溫暖都不行，

because then you end up too hot like Venus,

因為這樣會像金星一樣太熱，

and you can't have liquid water.

而且沒有液態水。

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

但是如果你的大氣層太少， 而且太薄太冷，

you end up like Mars, too cold.

結果就會像火星一樣太冷。

So Venus is too hot, Mars is too cold,

所以金星太熱，火星太冷，

and Earth is just right.

地球則是剛剛好。

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

看看我後面的照片，你自然會看到

where life can survive in our solar system.

我們的太陽系 哪裡有生命可以存活。

It's a Goldilocks-type problem,

這是典型的 《金髮女孩與三隻熊》問題，

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

而且這太簡單了，小孩都能理解。

However,

然而，

I'd like to remind you of two things

我要提醒各位兩件事，

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

是《金髮女孩與三隻熊》故事中， 常常被我們忽略

but that I think are really relevant here.

但我認為非常切題的事。

Number one:

第一：

if Mama Bear's bowl is too cold

金髮女孩走進屋時， 如果熊媽媽碗裡的粥太冷，

when Goldilocks walks into the room,

does that mean it's always been too cold?

那是指粥早就冷了？

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

還是曾有剛剛好的時間？

When Goldilocks walks into the room determines the answer

金髮女孩走進屋的時間決定了

that we get in the story.

故事的答案。

And the same is true with planets.

行星也一樣。

They're not static things. They change.

行星不是靜態的東西。 它們一直在改變。

They vary. They evolve.

它們變化，它們演化。

And atmospheres do the same.

大氣層也一樣。

So let me give you an example.

我舉一個例子。

Here's one of my favorite pictures of Mars.

這是我很愛的一張火星照片。

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

這既非最高解析度，也並非最美，

it's not the most recent image,

更不是最新的照片，

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

但這張照片顯示河床切過行星表面；

riverbeds carved by flowing, liquid water;

被流動、液態水切割出的河床；

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

河床要上百、上千 甚至上萬年才能形成。

This can't happen on Mars today.

現在的火星不可能發生這件事。

The atmosphere of Mars today is too thin and too cold

現在的火星大氣層太薄太冷，

for water to be stable as a liquid.

水因而不能維持液態。

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

這一張照片告訴我們 火星的大氣改變了，

and it changed in big ways.

而且改變很大。

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

它從我們定義的適居狀態 變成現在的樣子，

because the three requirements for life were present long ago.

因為生命三大要素 在很久以前曾經出現過。

Where did that atmosphere go

本來能讓水在地表 維持液態的大氣去了哪裡？

that allowed water to be liquid at the surface?

Well, one idea is it escaped away to space.

嗯，有人說它逃逸到宇宙。

Atmospheric particles got enough energy to break free

大氣粒子有足夠的能量

from the gravity of the planet,

逃脫此行星的重力，

escaping away to space, never to return.

散逸到太空，一去不返。

And this happens with all bodies with atmospheres.

這種現象在有大氣的 星體上都會發生。

Comets have tails

彗星的尾巴

that are incredibly visible reminders of atmospheric escape.

正是大氣逃逸絕佳的視覺提醒。

But Venus also has an atmosphere that escapes with time,

但是金星的大氣也會隨時間逃逸，

and Mars and Earth as well.

火星及地球也一樣。

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

這只是程度及規模的問題。

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

所以我們要找出逃逸的速率，

so we can explain this transition.

才能解釋這種轉變。

How do atmospheres get their energy for escape?

大氣怎麼得到逃逸所需的能量？

How do particles get enough energy to escape?

粒子怎麼得到足以逃逸的能量？

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

如果我們簡化一下來看， 有兩種方式。

Number one, sunlight.

第一，陽光。

Light emitted from the sun can be absorbed by atmospheric particles

從太陽射出的光被大氣粒子吸收，

and warm the particles.

使粒子增溫。

Yes, I'm dancing, but they --

是，我是在跳舞，不過它們──

(Laughter)

（笑聲）

Oh my God, not even at my wedding.

天啊，我在自己的婚禮上都沒跳。

(Laughter)

（笑聲）

They get enough energy to escape and break free

它們得到足夠的能量逃逸

from the gravity of the planet just by warming.

並掙脫重力， 這一切只要增溫就夠了。

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

得到能量的第二種方法是太陽風。

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

這些是從太陽表面噴出的 粒子、團塊及物質，

and they go screaming through the solar system

而且它們在太陽系裡

at 400 kilometers per second,

以每秒 400 公里的速率呼嘯而過，

sometimes faster during solar storms,

在太陽風暴期間有時候還更快，

and they go hurtling through interplanetary space

而且它們飛馳通過行星際空間，

towards planets and their atmospheres,

朝著行星及其大氣飛去，

and they may provide energy

因而它們也可以提供能量

for atmospheric particles to escape as well.

讓大氣粒子逃逸。

This is something that I'm interested in,

這就是我感興趣的東西，

because it relates to habitability.

因為這跟適居性有關。

I mentioned that there were two things about the Goldilocks story

我曾說過金髮女孩的故事中有兩件事

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

我要你們注意並提醒你們一下，

and the second one is a little bit more subtle.

第二件事更微妙一點。

If Papa Bear's bowl is too hot,

如果熊爸爸碗裡的粥太燙了，

and Mama Bear's bowl is too cold,

而熊媽媽的粥太冷了，

shouldn't Baby Bear's bowl be even colder

那熊寶寶的粥不就應該更冷了，

if we're following the trend?

如果我們順著趨勢想？

This thing that you've accepted your entire life,

你一輩子都沒懷疑過的這件事，

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

仔細一想後可能沒那麼簡單。

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

當然，行星的溫度取決於 它與太陽的距離。

This has to play into habitability.

這就與適居性有關。

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

但是我們可能還必須考慮其它事。

Maybe it's the bowls themselves

可能碗本身

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

也會決定這個故事的結局，

what is just right.

也就是「剛剛好」的問題。

I could talk to you about a lot of different characteristics

我可以跟大家講很多

這三個行星不同的特性，

of these three planets

that may influence habitability,

這些特性可能也會影響適居性，

but for selfish reasons related to my own research

但是我有私心， 因為那跟我的研究有關係，

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

而且站在這裡拿著遙控器的是我， 不是你們──

(Laughter)

（笑聲）

I would like to talk for just a minute or two

所以我只跟你們講一兩分鐘就好，

about magnetic fields.

來談一下磁場。

Earth has one; Venus and Mars do not.

地球有磁場；金星及火星沒有。

Magnetic fields are generated in the deep interior of a planet

磁場在行星內部深處產生，

by electrically conducting churning fluid material

由導電的液態物質環繞流動

that creates this big old magnetic field that surrounds Earth.

而產生這個環繞地球的 巨大古老磁場。

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

如果你有羅盤， 你會知道哪邊是北邊。

Venus and Mars don't have that.

金星與火星沒有這個。

If you have a compass on Venus and Mars,

如果你在金星及火星上用羅盤，

congratulations, you're lost.

恭喜喔！你迷路了。

(Laughter)

（笑聲）

Does this influence habitability?

這會影響適居性嗎？

Well, how might it?

又怎麼影響？

Many scientists think that a magnetic field of a planet

許多科學家認為行星的磁場

serves as a shield for the atmosphere,

就像大氣層的防護罩，

deflecting solar wind particles around the planet

使在行星四周的太陽風粒子偏轉，

in a bit of a force field-type effect

有點像（星際爭霸戰） 力場防護罩效應，

having to do with electric charge of those particles.

因為跟這些粒子的電荷有關。

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

我喜歡把它比喻為沙拉吧上面 擋噴嚏的防護罩。

(Laughter)

（笑聲）

And yes, my colleagues who watch this later will realize

是的，以後看這片的同僚會發現，

this is the first time in the history of our community

這是史上頭一遭有人在我們這行

that the solar wind has been equated with mucus.

把太陽風等同為黏液。

(Laughter)

（笑聲）

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

好吧，所以這個效應， 就是地球可以受到保護

for billions of years,

幾十億年，

because we've had a magnetic field.

因為我們有磁場。

Atmosphere hasn't been able to escape.

大氣至今無法逃脫。

Mars, on the other hand, has been unprotected

另一方面，火星沒有受到保護，

because of its lack of magnetic field,

因為它沒有磁場，

and over billions of years,

所以幾十億年來，

maybe enough atmosphere has been stripped away

可能已經揭掉了夠多的大氣，

to account for a transition from a habitable planet

使這個原本適居的行星轉變為

to the planet that we see today.

今天我們看到的樣子。

Other scientists think that magnetic fields

其他科學家認為磁場的

may act more like the sails on a ship,

作用可能更像船上的帆，

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

讓行星能與太陽風的能量 產生更多交互作用，

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

比自身的交互作用還要更多。

The sails may gather energy from the solar wind.

帆可以聚集風的能量。

The magnetic field may gather energy from the solar wind

磁場可以聚集太陽風的能量，

that allows even more atmospheric escape to happen.

讓更多大氣逃逸。

It's an idea that has to be tested,

這個理論還需要證明，

but the effect and how it works

但是其影響及作用方式

seems apparent.

看起來很明顯。

That's because we know

那是因為我們知道

energy from the solar wind is being deposited into our atmosphere

太陽風的能量會注入

地球上的大氣層。

here on Earth.

That energy is conducted along magnetic field lines

那股能量順著磁力線傳導，

down into the polar regions,

向下導入兩極，

resulting in incredibly beautiful aurora.

產生炫麗無比的極光。

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

如果你曾看過極光，那真是壯麗！

We know the energy is getting in.

我們知道能量進來了。

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

我們試著測量有多少粒子跑出去，

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

還有磁場是否 以任何方式影響這一點。

So I've posed a problem for you here,

所以我丟了一個問題給各位，

but I don't have a solution yet.

但是我還沒有答案。

We don't have a solution.

我們沒有解答。

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

但是我們正在找。 怎麼找呢？

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

嗯，我們送了幾艘太空船 到這三個行星上。

Some of them are orbiting now,

有些已經在軌道上環繞了，

including the MAVEN spacecraft which is currently orbiting Mars,

包括目前正在環繞火星的 MAVEN （火星大氣與揮發物演化任務）太空船，

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

我有參與這項計畫，

而且由此地的科羅拉多大學領導。

out of the University of Colorado.

It's designed to measure atmospheric escape.

我們用它測量大氣逃逸。

We have similar measurements from Venus and Earth.

我們對金星及地球也做了 類似的測量。

Once we have all our measurements,

一旦我們收及到所有的測量數據，

we can combine all these together, and we can understand

我們就能把這些綜合起來， 我們就能了解

how all three planets interact with their space environment,

這三個行星如何與太空環境，

with the surroundings.

與它們周邊的環境交互作用，

And we can decide whether magnetic fields are important for habitability

我們就能決定磁場 對適居性的重要與否。

or not.

Once we have that answer, why should you care?

一旦我們有了答案， 我們為什麼要在意？

I mean, I care deeply ...

我是說，我很在意──

And financially as well, but deeply.

財務上我也很在意啦！ 不過真的很在意。

(Laughter)

（笑聲）

First of all, an answer to this question

首先，這個問題的答案

will teach us more about these three planets,

會教我們更多這三個行星的事，

Venus, Earth and Mars,

金星、地球及火星，

not only about how they interact with their environment today,

不只是它們如何 與現今的環境交互作用，

but how they were billions of years ago,

還有幾十億以前的交互作用，

whether they were habitable long ago or not.

很久以前的適居性如何。

It will teach us about atmospheres

它會教我們很多

that surround us and that are close.

環繞及靠近我們的大氣層的事。

But moreover, what we learn from these planets

此外，我們從這幾個行星學到的，

can be applied to atmospheres everywhere,

可以應用到別處的大氣層，

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

包括我們正在觀察的幾個行星， 它們環繞著其它恆星。

For example, the Kepler spacecraft,

舉個例子，克卜勒太空望遠鏡，

which is built and controlled here in Boulder,

就在波德這裡建造並控制，

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

已經觀察了郵票大小的天空

for a couple years now,

好幾年了，

and it's found thousands of planets --

它發現了數千個行星──

in one postage stamp-sized region of the sky

就在郵票大小的一小片天空中，

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

這片天跟其它部分的天空 沒什麼不同。

We've gone, in 20 years,

在 20 年內，我們從以為

from knowing of zero planets outside of our solar system,

太陽系以外沒有行星，

to now having so many,

到現在我們知道有這麼多，

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

甚至不知道該從哪一個 開始調查起。

Any lever will help.

任何方法都有幫助。

In fact, based on observations that Kepler's taken

其實，從克卜勒太空望遠鏡

and other similar observations,

及其它類似的觀測所發現的來看，

we now believe that,

我們現在相信

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

光是在我們銀河系的 二千億顆星星裡，

on average, every star has at least one planet.

每顆星平均都至少有一個行星。

In addition to that,

除此之外，

estimates suggest there are somewhere between 40 billion and 100 billion

估計這些行星中 還有約四百億到一千億顆，

of those planets that we would define as habitable

我們可以定義為適居，

in just our galaxy.

僅僅在我們的銀河！

We have the observations of those planets,

我們有這些行星的觀測，

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

但是我們還不知道 哪一個是適合居住的。

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

這就跟困在 TED 這塊紅地毯上一樣，

(Laughter)

（笑聲）

on a stage

在舞台上，

and knowing that there are other worlds out there

你知道還有其它的世界存在，

and desperately wanting to know more about them,

極度想要更了解他們，

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

想調查並找出是不是有一兩個

are a little bit like you.

和自己有點像。

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

你做不了這件事， 你去不了那裡，還不行。

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

所以你必須使用你手邊

為了金星、地球及火星 而發展的工具，

for Venus, Earth and Mars,

and you have to apply them to these other situations,

還必須將它們應用在 這些不同的狀況下，

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

希望自己能從數據做出合理的推斷，

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

希望自己能選出最好的

for habitable planets, and those that are not.

適居行星，還要找出不合適的。

In the end, and for now, at least,

最終，至少目前，

this is our red spot, right here.

這是我們的紅地毯，就在這裡。

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

這是目前我們所知唯一適居的行星，

although very soon we may come to know of more.

雖然我們可能很快就會發現 還有其它的。

But for now, this is the only habitable planet,

但是目前，這是唯一適居的行星，

and this is our red spot.

這就是我們的紅地毯。

I'm really glad we're here.

我真的很高興我們都在這裡。

Thanks.

謝謝。

(Applause)

（掌聲）