What a planet needs to sustain life | Dave Brain

Translator: Tammy Lee Reviewer: Alan Watson

I'm really glad to be here.

我好高興可以喺度

I'm glad you're here,

我都好高興你哋可以喺度

because that would be a little weird.

因爲冇你哋嘅話，會些少奇怪

I'm glad we're all here.

我好高興我哋都喺度

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

我講嘅「呢度」 唔係指 TED 呢度

Or here.

或者呢度

But here.

係呢度

I mean Earth.

我指嘅係地球

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

而我所講嘅「我哋」唔係指 呢度演講廳嘅咁多位

but life,

而係生命

all life on Earth --

地球上所有嘅生命

(Laughter)

（笑聲）

from complex to single-celled,

由複雜細胞到單細胞

from mold to mushrooms

由黴菌到蘑菇

to flying bears.

到飛天熊都係

(Laughter)

（笑聲）

The interesting thing is,

有趣嘅係

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

地球係我哋知道唯一有生命嘅地方

8.7 million species.

八百七十萬種生物

We've looked other places,

我哋人類其實有睇過其他地方

maybe not as hard as we should or we could,

不過可能冇畀心機搵喇

但係我哋搵咗之後都冇發現有生物

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

Earth is the only place we know of with life.

地球係我哋知道唯一有生命嘅地方

Is Earth special?

地球特殊嗎？

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

呢個問題由我細時就已經想知

since I was a small child,

and I suspect 80 percent of this auditorium

而我估呢座禮堂八成嘅人 都諗過同樣嘅事

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

亦都想知道答案

To understand whether there are any planets --

要知道有冇其他行星

out there in our solar system or beyond --

喺我哋太陽系或者其他地方 能夠支持生命

that can support life,

the first step is to understand what life here requires.

第一步需要了解地球嘅生命需要啲乜

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

事實證明，喺呢八百七十萬個物種之中

life only needs three things.

生命只需要三件事

On one side, all life on Earth needs energy.

三張相嘅一邊 地球上所有生命都需要能量

Complex life like us derives our energy from the sun,

好似我哋咁嘅複合生物體 需要從太陽取得能量

but life deep underground can get its energy

但係地下深處嘅生物 可以由化學反應取得能量

from things like chemical reactions.

There are a number of different energy sources

能量嘅來源喺每個星球都有好多種

available on all planets.

On the other side,

相片另一邊

all life needs food or nourishment.

所有生命都需要食物或者營養

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

咁聽起嚟係過分要求

尤其當你想要一隻多汁嘅番茄時

(Laughter)

（笑聲）

However, all life on Earth derives its nourishment

但係地球上所有嘅生命 只需由六種化學元素取得營養

from only six chemical elements,

and these elements can be found on any planetary body

呢啲元素都可以喺我哋嘅太陽系 任何一個行星上面發現

in our solar system.

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

所以剩低中間嘅嘢最難達到

the thing that's hardest to achieve.

Not moose, but water.

唔係麋鹿，係水

(Laughter)

（笑聲）

Although moose would be pretty cool.

雖然如果係麋鹿都幾型

(Laughter)

（笑聲）

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

唔係冰結嘅水，亦唔係氣態嘅水

而係液態水

This is what life needs to survive, all life.

水係所有生命生存都需要嘅嘢

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

太陽系好多星球都冇液態水

and so we don't look there.

所以我哋唔去呢啲星球度搵

Other solar system bodies might have abundant liquid water,

但有啲太陽系嘅星球可能有大量液態水

even more than Earth,

甚至多過地球

but it's trapped beneath an icy shell,

但啲水都係困喺冰層底下

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

所以好難接近，好難用到

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

亦都令到我哋好難探測 冰層下面有冇生命

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

咁只剩低幾個星球值得考慮

So let's make the problem simpler for ourselves.

所以等我哋簡化一下問題

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

我哋只要諗喺星球表面搵到液態水就好

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

咁我哋嘅太陽系裡邊 只有三個星球可以諗

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

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

按太陽嘅距離依次序為： 金星、地球、火星

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

因為你想大氣層畀到水係液體狀態

You have to be very careful with that atmosphere.

所以要對大氣層非常講究

大氣層唔可以太厚或者太暖

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

because then you end up too hot like Venus,

因為咁樣嘅話會好似金星一樣咁熱

and you can't have liquid water.

而且冇可能有液態水

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

但係如果你嘅大氣層太薄太凍

you end up like Mars, too cold.

結果就會好似火星一樣咁凍

So Venus is too hot, Mars is too cold,

所以金星太熱，火星太凍

and Earth is just right.

地球就啱啱好

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

睇下我後邊嘅相，你自然會睇到

where life can survive in our solar system.

我哋嘅太陽系邊度可以有生命

It's a Goldilocks-type problem,

呢個係「金髮女孩 與三隻熊故事」嘅問題

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

簡單到兒童都可以理解

However,

不過，我想提醒各位兩件事

I'd like to remind you of two things

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

喺金髮女孩與三隻熊個故事裡面

but that I think are really relevant here.

我哋經常忽略、但我認為非常切題嘅事

Number one:

第一

if Mama Bear's bowl is too cold

當金髮女孩行入屋時

when Goldilocks walks into the room,

如果熊媽媽碗粥太凍

does that mean it's always been too cold?

咁碗粥係咪一路都係凍嘅呢？

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

定係喺之前係暖嘅呢？

When Goldilocks walks into the room determines the answer

金髮女孩行入屋時就一口咬定咗個答案

that we get in the story.

And the same is true with planets.

行星都一樣

They're not static things. They change.

行星唔係靜態嘅嘢，佢哋一直改變緊

They vary. They evolve.

佢哋會變化、會演化

And atmospheres do the same.

大氣層都一樣

So let me give you an example.

我舉一個例子

Here's one of my favorite pictures of Mars.

呢個係我最鍾意嘅火星圖片

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

佢唔係最高解析度，亦唔係最靚

it's not the most recent image,

都唔係最新嘅相

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

但係佢顯示行星表面嘅河床

液態水流動而形成嘅河床

riverbeds carved by flowing, liquid water;

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先能形成

This can't happen on Mars today.

依家嘅火星冇可能發生呢件事

The atmosphere of Mars today is too thin and too cold

依家嘅火星大氣層太薄太冷

for water to be stable as a liquid.

導致水唔可以維持液態

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

呢張相話我哋知火星嘅大氣層改變咗

and it changed in big ways.

而且改變好大

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

佢由可居住嘅狀態變成依家咁

because the three requirements for life were present long ago.

以前之所以可居住係因為 生命三大要素曾經喺嗰度出現過

以前大氣層可以令地表維持液態水

Where did that atmosphere go

that allowed water to be liquid at the surface?

但依家火星嘅大氣層去咗邊度？

Well, one idea is it escaped away to space.

一種理論係佢逃逸去到太空

Atmospheric particles got enough energy to break free

話大氣粒子有足夠嘅能量 走出行星嘅引力

from the gravity of the planet,

escaping away to space, never to return.

散逸到太空，一去不返

And this happens with all bodies with atmospheres.

呢種現象喺有大氣層嘅星球上面 都會發生

Comets have tails

彗星嘅尾就係大氣逃逸嘅最佳例子

that are incredibly visible reminders of atmospheric escape.

But Venus also has an atmosphere that escapes with time,

但係金星嘅大氣都會隨著時間逃逸

火星與地球都會

and Mars and Earth as well.

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

只不過係程度同規模嘅問題

所以我哋要搵出逃逸嘅速率 先能夠解釋大氣層消失嘅現象

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

so we can explain this transition.

How do atmospheres get their energy for escape?

大氣點得到逃逸所需嘅能量？

How do particles get enough energy to escape?

粒子點得到足以逃逸嘅能量？

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

如果我哋簡單嚟睇，有兩種方法

Number one, sunlight.

第一，陽光

Light emitted from the sun can be absorbed by atmospheric particles

大氣粒子吸收太陽發出嘅光

and warm the particles.

令到粒子增溫

Yes, I'm dancing, but they --

係，我跳緊舞，不過粒子佢哋…

(Laughter)

（笑聲）

Oh my God, not even at my wedding.

該煨，我喺自己嘅婚禮都冇跳過…

(Laughter)

（笑聲）

They get enough energy to escape and break free

佢哋增溫就已經得到足夠嘅能量 去逃離引力

from the gravity of the planet just by warming.

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

第二種方法係靠太陽風

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

由太陽表面噴出嘅粒子、物質

and they go screaming through the solar system

會喺太陽系裡邊 以每秒 400 公里嘅速度呼嘯而過

at 400 kilometers per second,

sometimes faster during solar storms,

太陽風暴嚟嗰陣有時仲會快啲添

and they go hurtling through interplanetary space

佢哋穿梭行星之間 向著行星同行星嘅大氣飛去

towards planets and their atmospheres,

and they may provide energy

佢哋可能畀到大氣粒子能量去逃逸

for atmospheric particles to escape as well.

This is something that I'm interested in,

呢個就係我覺得有興趣嘅嘢

because it relates to habitability.

因為呢個同適居性有關

I mentioned that there were two things about the Goldilocks story

我講過金髮女孩嘅故事 有兩樣嘢你哋要留意一下

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

and the second one is a little bit more subtle.

而第二件事更加微妙︰

If Papa Bear's bowl is too hot,

如果熊爸爸碗粥太熱

and Mama Bear's bowl is too cold,

而熊媽媽碗粥太凍

shouldn't Baby Bear's bowl be even colder

咁熊寶寶碗粥咪應該更加凍？

如果我哋跟著個趨勢諗

if we're following the trend?

This thing that you've accepted your entire life,

呢件你成世人都以為嘅事 如果仔細諗下，可能冇咁簡單

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

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

當然，行星溫度取決於佢同太陽嘅距離

This has to play into habitability.

就同適居性有關

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

但係我哋可能需要考慮其他事情

Maybe it's the bowls themselves

可能碗本身都會決定個故事嘅結局︰

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

what is just right.

亦即係乜為之啱啱好

I could talk to you about a lot of different characteristics

我可以同大家講好多 關於呢三個行星唔同嘅特性

of these three planets

that may influence habitability,

點樣影響適居性

but for selfish reasons related to my own research

但係因為我研究嘅關係 同埋因為我係講者

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

(Laughter)

（笑聲）

I would like to talk for just a minute or two

所以我想花一兩分鐘同你哋講下磁場

about magnetic fields.

Earth has one; Venus and Mars do not.

地球有磁場；金星同火星就冇

Magnetic fields are generated in the deep interior of a planet

地球內部深處有一啲電導液體物質

by electrically conducting churning fluid material

呢啲電導液體物質流動嗰陣 會形成地球嘅磁場

that creates this big old magnetic field that surrounds Earth.

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

如果你有指南針，你就會知道邊邊係北

但金星同火星都冇磁場

Venus and Mars don't have that.

If you have a compass on Venus and Mars,

如果你喺金星同火星上面用指南針

congratulations, you're lost.

恭喜！你盪失路

(Laughter)

（笑聲）

Does this influence habitability?

磁場會影響適居性嗎？

Well, how might it?

會點影響？

Many scientists think that a magnetic field of a planet

好多科學家認為行星嘅磁場 就好似大氣層嘅防護罩

serves as a shield for the atmosphere,

deflecting solar wind particles around the planet

令行星四周嘅太陽粒子改變方向

in a bit of a force field-type effect

屬於力場效應嘅一種

having to do with electric charge of those particles.

亦都同粒子嘅電荷有關

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

我鐘意將佢比喻為 麫包鋪廚窗揭得開嘅玻璃蓋

(Laughter)

（笑聲）

And yes, my colleagues who watch this later will realize

係嘅，之後睇呢段片嘅同事會發覺

this is the first time in the history of our community

呢個係我哋第一次 將太陽風等同為口水唾沫

that the solar wind has been equated with mucus.

(Laughter)

（笑聲）

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

好，所以地球之所以 幾十億年嚟都受到保護

for billions of years,

because we've had a magnetic field.

全因我哋有磁場

Atmosphere hasn't been able to escape.

以至大氣冇辦法逃脫

Mars, on the other hand, has been unprotected

另一方面因為火星冇磁場

because of its lack of magnetic field,

火星嘅大氣冇保護

and over billions of years,

以致可能幾十億年嚟火星失去嘅大氣

maybe enough atmosphere has been stripped away

to account for a transition from a habitable planet

足以令到呢個原本可以居住嘅行星

to the planet that we see today.

變成今日我哋睇到嘅樣

其他科學家認為磁場可能更似船嘅帆

Other scientists think that magnetic fields

may act more like the sails on a ship,

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

令行星可以同太陽風交換更多嘅能量

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

The sails may gather energy from the solar wind.

磁場可以收集太陽風嘅能量 畀更加多嘅大氣脫逃到

The magnetic field may gather energy from the solar wind

that allows even more atmospheric escape to happen.

It's an idea that has to be tested,

呢個理論仲需要去證實

but the effect and how it works

但係佢嘅效應同運作方式睇起來好明顯

seems apparent.

That's because we know

咁係因為我哋知道

energy from the solar wind is being deposited into our atmosphere

太陽風嘅能量已經注入緊 我哋地球嘅大氣層度

here on Earth.

That energy is conducted along magnetic field lines

嗰股能量順著磁力線傳導

向下導入兩極

down into the polar regions,

resulting in incredibly beautiful aurora.

化成無比璀璨嘅極光

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

如果你有睇過極光，你就知佢有幾壯麗

We know the energy is getting in.

我哋知道能量入緊嚟

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

我哋想計下有幾多粒子逃逸

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

同埋睇下磁場係咪真係有影響

So I've posed a problem for you here,

我有一個問題畀大家

but I don't have a solution yet.

但係我未有答案，我們冇答案

We don't have a solution.

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

但係我哋努力緊。我哋係點努力呢？

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

我哋送咗太空船去呢三個行星度

Some of them are orbiting now,

有啲圍繞緊行星

including the MAVEN spacecraft which is currently orbiting Mars,

包括 MAVEN 太空船 目前喺火星嘅軌道上面

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

呢項計劃我都有參與

而且係由呢度嘅科羅拉多大學帶領

out of the University of Colorado.

It's designed to measure atmospheric escape.

個計劃為咗測量大氣逃脫

我哋喺金星同地球都有類似嘅量度

We have similar measurements from Venus and Earth.

Once we have all our measurements,

當我哋集齊所有嘅量度數據

we can combine all these together, and we can understand

我哋就可以將佢哋併埋一齊

就可以了解呢三個行星 點樣同周圍嘅太空環境互動

how all three planets interact with their space environment,

with the surroundings.

And we can decide whether magnetic fields are important for habitability

我哋就可以決定磁場係咪對適居性重要

or not.

Once we have that answer, why should you care?

就算我哋有咗答案 但係點解你哋要咁在乎？

I mean, I care deeply ...

我意思係，我好在乎

And financially as well, but deeply.

我亦都在乎研究經費

(Laughter)

（笑聲）

First of all, an answer to this question

首先，呢個問題嘅答案

will teach us more about these three planets,

會教我哋更多關於 金星、地球以及火星嘅事

Venus, Earth and Mars,

唔單止包括佢哋點樣同現今嘅環境互動

not only about how they interact with their environment today,

but how they were billions of years ago,

仲包括佢哋幾十億以前嘅狀態

whether they were habitable long ago or not.

同埋佢哋好耐以前係咪適合居住

It will teach us about atmospheres

答案會揭示大氣層嘅嘢

that surround us and that are close.

But moreover, what we learn from these planets

另外，我哋從呢幾個行星嘅 大氣層學到嘅知識

can be applied to atmospheres everywhere,

可以應用喺其他星球嘅大氣層度

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

包括我哋觀察緊嘅 幾個環繞著其他恆星嘅行星

For example, the Kepler spacecraft,

舉個例子，喺波德呢度 建造同埋控制嘅哈勃太空望遠鏡

which is built and controlled here in Boulder,

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

已經好幾年觀察緊 一塊郵票咁大嘅天空範圍

for a couple years now,

and it's found thousands of planets --

佢目前已經喺郵票咁大嘅天空裏面 發現咗幾千個行星

in one postage stamp-sized region of the sky

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

而我哋唔覺呢塊天空 同其他天空有咩唔同

We've gone, in 20 years,

廿年裏邊

from knowing of zero planets outside of our solar system,

我哋由一個太陽系以外嘅 行星都唔認識

to now having so many,

到依家知道有咁多行星

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

我哋都唔知應該由邊度開始探索

Any lever will help.

任何幫手都歡迎

In fact, based on observations that Kepler's taken

其實，跟據哈勃太空望遠鏡得到嘅觀察

and other similar observations,

加上其他類似嘅觀測，我哋宜家相信

we now believe that,

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

剩係我哋銀河系二千億個星裡邊

on average, every star has at least one planet.

平均每個恆星至少有一個行星

In addition to that,

除此之外，單單喺我哋嘅銀河

estimates suggest there are somewhere between 40 billion and 100 billion

我哋估計有大概四百億 到一千億個行星係適居嘅

of those planets that we would define as habitable

in just our galaxy.

We have the observations of those planets,

我哋得到呢啲行星嘅觀測資料

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

但係我哋仲未知邊一個係適合居住嘅

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

有點似被困喺台上嘅呢塊紅地氈一樣

(Laughter)

（笑聲）

on a stage

and knowing that there are other worlds out there

但係你又知道仲有其他世界存在

and desperately wanting to know more about them,

你又極想了解佢哋

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

你又想調查睇下有冇一兩個星球 好似自己嘅星球

are a little bit like you.

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

但係你就係做唔到，你去唔到

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

所以你要用上 為到金星、地球同火星開發嘅工具

for Venus, Earth and Mars,

and you have to apply them to these other situations,

你要將工具用喺其他情況度

並確保能夠從數據裏面作出合理嘅推斷

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

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

從而揀出最有可能適居嘅行星

for habitable planets, and those that are not.

同埋搵出最冇可能適居嘅行星

最終，同埋至少目前

In the end, and for now, at least,

this is our red spot, right here.

呢個就係我哋嘅紅地氈，就喺呢度

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

呢個係目前我哋所知唯一適居嘅行星

although very soon we may come to know of more.

雖然好快我哋可能會發現仲有其他嘅

But for now, this is the only habitable planet,

但係目前，呢個係唯一適居嘅行星

and this is our red spot.

呢個就係我哋嘅紅地氈

I'm really glad we're here.

我真係好高興我哋都喺度

Thanks.

多謝

(Applause)

（掌聲）