3 moons and a planet that could have alien life | James Green

譯者: Helen Chang 審譯者: SF Huang

Is there life beyond Earth in our solar system?

除地球外，太陽系中 還有其他生命存在嗎？

Wow, what a powerful question.

哇，大哉問！

You know, as a scientist --

身為科學家、

planetary scientist --

行星科學家，

we really didn't take that very seriously until recently.

直到最近我們才嚴肅、 認真地面對這個問題。

Carl Sagan always said,

卡爾‧薩根總是說：

"It takes extraordinary evidence for extraordinary claims."

「非凡的主張需有 非凡的證據來支持。」

And the claims of having life beyond Earth

地球之外有生命的主張，

need to be definitive,

必須是明確的、

they need to be loud

必須是響亮的、

and they need to be everywhere for us to be able to believe it.

必須隨處可見的，我們才能夠相信。

So how do we make this journey?

我們該如何展開這旅程呢？

What we decided to do

我們決定先尋找生命的要素。

is first look for those ingredients for life.

The ingredients of life are:

生命的要素是：

liquid water --

「液態水」──

we have to have a solvent,

必須有溶劑，

can't be ice, has to be liquid.

不能是冰，必須是液態的。

We also have to have energy.

我們也必須有「能量。」

We also have to have organic material --

還須有「有機物」──

things that make us up,

它組成我們人體架構，

but also things that we need to consume.

並提供我們攝食所需。

So we have to have these elements

環境中必須長期有這三種元素，

in environments for long periods of time

for us to be able to be confident that life,

才能讓我們相信：

生命，在它初萌的那一刻，

in that moment when it starts,

迸出火花，

can spark and then grow and evolve.

然後得以成長和演化。

Well, I have to tell you that early in my career,

但我必須坦白，

在早期職涯中檢視這三個要素時，

when we looked at those three elements,

I didn't believe that they were beyond Earth

我不相信在地球之外，

它們曾出現或存在過任何地方。

in any length of time and for any real quantity.

Why? We look at the inner planets.

為什麼？

讓我們看看太陽系的內行星：

Venus is way too hot -- it's got no water.

金星太熱，沒有水；

Mars -- dry and arid.

火星既乾又旱，沒有水；

It's got no water.

And beyond Mars,

太陽系中比火星更遠的水 全部凍成了固態的冰。

the water in the solar system is all frozen.

But recent observations have changed all that.

但最近的觀測讓這一切改觀了，

It's now turning our attention to the right places

使我們將注意力轉向正確的地方，

for us to take a deeper look

進一步去探究，

and really start to answer our life question.

真正地開始回答生命的問題。

So when we look out into the solar system,

所以，我們探究太陽系

where are the possibilities?

生命的可能性存在哪裡呢？

We're concentrating our attention on four locations.

我們將注意力集中於四顆星體：

The planet Mars

火星，

and then three moons of the outer planets:

和外行星中的三個衛星：

Titan, Europa and small Enceladus.

泰坦（土衛六）、歐羅巴（木衛二）， 和小小的恩克拉多斯（土衛二）。

So what about Mars?

火星是什麼狀況呢？

Let's go through the evidence.

讓我們來討論一下證據。

Well, Mars we thought was initially moon-like:

起初我們以為火星像月亮：

full of craters, arid and a dead world.

佈滿隕石坑洞、乾旱荒蕪， 是個死寂的世界。

And so about 15 years ago,

大約 15 年前，

we started a series of missions to go to Mars

我們開始了一系列的火星任務，

and see if water existed on Mars in its past

查看火星過去是否有水存在，

that changed its geology.

改變了它的地質。

We ought to be able to notice that.

我們本應查覺得到。

And indeed we started to be surprised right away.

確實，我們一開始就很訝異，

Our higher resolution images show deltas and river valleys and gulleys

因高解析度的影像顯示，

那裡曾有過三角洲、河谷，和溝渠。

that were there in the past.

And in fact,

事實上，

Curiosity --

好奇號探測車已在 火星表面上漫遊 3 年了；

which has been roving on the surface now for about three years --

has really shown us that it's sitting in an ancient river bed,

我們看到它停在一條古老的河床上，

where water flowed rapidly.

在那曾有湍急的水流過，

And not for a little while,

時間不短，

perhaps hundreds of millions of years.

可能持續流過數億年之久。

如果主要元素都在那裡，

And if everything was there,

including organics,

有機物包括在內，

perhaps life had started.

也許生命曾誕生過。

Curiosity has also drilled in that red soil

好奇號在紅土上鑽洞，

and brought up other material.

挖出了其他的物質。

And we were really excited when we saw that.

我們檢視後，非常地興奮，

Because it wasn't red Mars,

因為不是紅色，而是灰色的物質：

it was gray material,

it's gray Mars.

灰色的火星。

We brought it into the rover,

把挖出的物質帶回車裡辨識，

we tasted it,

and guess what?

你猜怎麼著？

We tasted organics --

我們辨識出有機物：

carbon, hydrogen, oxygen,

碳、氫、氧、

nitrogen, phosphorus, sulfur --

氮、磷、硫，

they were all there.

全都在那裡。

So Mars in its past,

所以，過去的火星

with a lot of water,

曾有過很多的水，

perhaps plenty of time,

也許曾有很長的一段時間，

could have had life,

曾有過生命、曾有過生命的火花、

could have had that spark,

could have grown.

曾有過成長的生命。

And is that life still there?

那時的生命，現在還存在嗎？

We don't know that.

我們不知道。

But a few years ago

但幾年前，

we started to look at a number of craters.

我們開始細看一些隕石坑。

During the summer,

在夏季，

dark lines would appear down the sides of these craters.

沿著這些隕石坑的邊緣 會出現深色的條紋。

The more we looked,

我們檢視越多的隕石坑，

the more craters we saw,

the more of these features.

就看到越多這樣的特點，

We now know more than a dozen of them.

現在已知超過十二個。

A few months ago the fairy tale came true.

幾個月前，神話成真了。

We announced to the world that we know what these streaks are.

我們向世界宣布 已經知道這些條紋是什麼：

It's liquid water.

是液態水。

These craters are weeping during the summer.

這些隕石坑在夏天滲流出液體；

Liquid water is flowing down these craters.

這些液態水流下隕石坑。

So what are we going to do now --

既已發現了水，接下來要做什麼呢？

now that we see the water?

Well, it tells us that Mars has all the ingredients necessary for life.

它告訴了我們，

火星具備了組成生命的必要成分，

In its past it had perhaps two-thirds of its northern hemisphere --

它北半球的三分之二 過去可能有過海洋，

there was an ocean.

It has weeping water right now.

現在有流下的水。

Liquid water on its surface.

它的星球表面有液態水。

It has organics.

它有有機物。

It has all the right conditions.

它有所有對的條件。

So what are we going to do next?

那麼，我們接下來要怎麼做呢？

We're going to launch a series of missions

我們要展開一系列的任務，

to begin that search for life on Mars.

開始尋找火星上的生命。

And now it's more appealing than ever before.

現在比以往任何時候都更有吸引力。

As we move out into the solar system,

再往更遠的太陽系裡，

here's the tiny moon Enceladus.

我們所看到的是小小的土衛二。

This is not in what we call the traditional habitable zone,

這個位置相對於太陽的距離， 並不是傳統上我們所認知的宜居區。

this area around the sun.

This is much further out.

這裡距離太陽更遠。

This object should be ice over a silicate core.

這個衛星，應該是 冰層覆蓋的矽酸鹽核心。

But what did we find?

但我們找到了什麼？

Cassini was there since 2006,

自 2006 年起， 卡西尼太空船就在那裡，

and after a couple years looked back after it flew by Enceladus

在飛過了土衛二幾年後再度回顧，

and surprised us all.

它的發現令我們全都大吃一驚。

Enceladus is blasting sheets of water out into the solar system

土衛二往太空噴出羽狀的水，

and sloshing back down onto the moon.

水又落回該衛星上。

What a fabulous environment.

多麼美妙的環境啊。

Cassini just a few months ago also flew through the plume,

幾個月前卡西尼飛過羽狀物，

and it measured silicate particles.

測到矽酸鹽顆粒。

Where does the silica come from?

二氧化矽來自何方？

It must come from the ocean floor.

一定來自海底。

The tidal energy is generated by Saturn,

土星產生的潮汐能，

pulling and squeezing this moon --

拉扯、擠壓這個衛星，

is melting that ice,

使它的冰層融化，

creating an ocean.

形成了海洋；

But it's also doing that to the core.

潮汐能同樣也拉扯、擠壓 這衛星的矽酸鹽核心。

Now, the only thing that we can think of

在地球上，我們想得到 唯一能類比的是

that does that here on Earth as an analogy ...

are hydrothermal vents.

「海底熱泉。」

Hydrothermal vents deep in our ocean were discovered in 1977.

海底熱泉於 1977 年 在海洋的深處被發現。

Oceanographers were completely surprised.

海洋學家非常地驚訝。

And now there are thousands of these below the ocean.

今天海底有著成千上萬的海底熱泉。

What do we find?

我們找到了什麼？

The oceanographers, when they go and look at these hydrothermal vents,

海洋學家發現海底熱泉裡，

they're teeming with life,

有著豐饒的生命，

regardless of whether the water is acidic or alkaline --

不管水是酸性或鹼性的，

doesn't matter.

與酸鹼無關。

So hydrothermal vents are a fabulous abode for life here on Earth.

所以，海底熱泉是地球上 生物的極佳住所。

So what about Enceladus?

那麼土衛二呢？

Well, we believe because it has water

我們相信土衛二因為有水，

and has had it for a significant period of time,

相當長的時間有水，

and we believe it has hydrothermal vents

也相信它有海底熱泉，

with perhaps the right organic material,

可能也有有機物存在，

it is a place where life could exist.

是個可能有生命存在的地方。

And not just microbial --

可能不只有微生物， 還有更複雜的生物，

maybe more complex because it's had time to evolve.

因為它有足夠的時間去演化。

Another moon, very similar,

另一個非常相似的衛星是歐羅巴。

is Europa.

Galileo visited Jupiter's system in 1996

伽利略號於 1996 年 造訪木星和週邊，

and made fabulous observations of Europa.

好好地觀察了歐羅巴。

Europa, we also know, has an under-the-ice crust ocean.

伽利略號任務讓我們得知

歐羅巴的冰殼下有海洋。

Galileo mission told us that, but we never saw any plumes.

以前我們並未看到任何羽狀噴泉，

But we didn't look for them.

是因為我們那時沒尋找。

Hubble,

哈伯太空望遠鏡，

just a couple years ago,

在兩年前

observing Europa,

觀察歐羅巴，

saw plumes of water

看到羽狀噴泉

spraying from the cracks in the southern hemisphere,

從南半球的裂縫噴出，

just exactly like Enceladus.

就像土衛二那樣。

These moons,

這些衛星

which are not in what we call a traditional habitable zone,

不是位於我們傳統認為的宜居區，

that are out in the solar system,

而是在太陽系的外區，

have liquid water.

卻有著液態水。

And if there are organics there,

如果那裡存在著有機物，

there may be life.

就可能有生命。

這是個好棒的發現，

This is a fabulous set of discoveries

because these moons have been in this environment like that

因為這些衛星處在這樣的環境中

for billions of years.

已經數十億年。

Life started here on Earth, we believe, after about the first 500 million,

我們認為地球的生命 始於最初的五億年，

and look where we are.

瞧瞧我們現在的模樣。

These moons are fabulous moons.

這些衛星真是讓人難以置信。

Another moon that we're looking at is Titan.

另一個我們想要探討的衛星是泰坦。

Titan is a huge moon of Saturn.

泰坦是土星的大衛星，

It perhaps is much larger than the planet Mercury.

體積可能比水星更大。

It has an extensive atmosphere.

它有遼闊的大氣層。

It's so extensive --

如此遼闊的大氣層，

and it's mostly nitrogen with a little methane and ethane --

主要成份是氮， 加上少量的甲烷和乙烷，

that you have to peer through it with radar.

必須用雷達穿透才能窺視它。

And on the surface, Cassini has found liquid.

卡西尼號在它的地表上發現了液體。

We see lakes ...

我們看到湖泊，

actually almost the size of our Black Sea in some places.

某些地方的湖泊幾乎 如我們的黑海一般大，

And this area is not liquid water;

湖裡並不是液態水，而是甲烷。

it's methane.

If there's any place in the solar system where life is not like us,

如果太陽系中存在著一個地方， 那裡的生命跟我們不同，

where the substitute of water is another solvent --

是以其它溶劑來代替水──

and it could be methane --

可能是甲烷 ──

it could be Titan.

那地點有可能是泰坦。

Well, is there life beyond Earth in the solar system?

除地球外，太陽系中 還有其他生命存在嗎？

We don't know yet,

我們還不知道，

but we're hot on the pursuit.

但我們正熱切地追尋著。

The data that we're receiving is really exciting

我們收到的數據真是令人興奮。

and telling us --

數據告訴我們、迫使我們

forcing us to think about this in new and exciting ways.

以新的、令人興奮的方式考量。

I believe we're on the right track.

我相信我們正走在正確的軌道上。

That in the next 10 years, we will answer that question.

未來 10 年我們將回答這個問題。

And if we answer it,

如果我們的回答是肯定的，

and it's positive,

then life is everywhere in the solar system.

那麼，太陽系中處處有生命。

Just think about that.

想想看，

We may not be alone.

我們可能並不孤單。

Thank you.

謝謝。

(Applause)

（掌聲）