Wow, what a powerful question.

除地球外，太陽系中 還有其他生命存在嗎？

You know, as a scientist --

哇，大哉問！

planetary scientist --

身為科學家、

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

行星科學家，

Carl Sagan always said,

直到最近我們才嚴肅、 認真地面對這個問題。

"It takes extraordinary evidence for extraordinary claims."

卡爾‧薩根總是說：

And the claims of having life beyond Earth

「非凡的主張需有 非凡的證據來支持。」

need to be definitive,

地球之外有生命的主張，

they need to be loud

必須是明確的、

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

必須是響亮的、

So how do we make this journey?

必須隨處可見的，我們才能夠相信。

What we decided to do

我們該如何展開這旅程呢？

is first look for those ingredients for life.

我們決定先尋找生命的要素。

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

才能讓我們相信：

for us to be able to be confident that life,

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，

when we looked at those three elements,

在早期職涯中檢視這三個要素時，

I didn't believe that they were beyond Earth

我不相信在地球之外，

in any length of time and for any real quantity.

它們曾出現或存在過任何地方。

Why? We look at the inner planets.

為什麼？

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

讓我們看看太陽系的內行星：

Mars -- dry and arid.

金星太熱，沒有水；

It's got no water.

火星既乾又旱，沒有水；

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.

但最近的觀測讓這一切改觀了，

But recent observations have changed all that.

使我們將注意力轉向正確的地方，

It's now turning our attention to the right places

進一步去探究，

for us to take a deeper look

真正地開始回答生命的問題。

and really start to answer our life question.

所以，我們探究太陽系

So when we look out into the solar system,

生命的可能性存在哪裡呢？

where are the possibilities?

我們將注意力集中於四顆星體：

We're concentrating our attention on four locations.

火星，

The planet Mars

和外行星中的三個衛星：

and then three moons of the outer planets:

泰坦（土衛六）、歐羅巴（木衛二）， 和小小的恩克拉多斯（土衛二）。

Titan, Europa and small Enceladus.

火星是什麼狀況呢？

So what about Mars?

讓我們來討論一下證據。

Let's go through the evidence.

起初我們以為火星像月亮：

Well, Mars we thought was initially moon-like:

佈滿隕石坑洞、乾旱荒蕪， 是個死寂的世界。

full of craters, arid and a dead world.

大約 15 年前，

And so about 15 years ago,

我們開始了一系列的火星任務，

we started a series of missions to go to Mars

查看火星過去是否有水存在，

and see if water existed on Mars in its past

改變了它的地質。

that changed its geology.

我們本應查覺得到。

We ought to be able to notice that.

確實，我們一開始就很訝異，

And indeed we started to be surprised right away.

因高解析度的影像顯示，

Our higher resolution images show deltas and river valleys and gulleys

那裡曾有過三角洲、河谷，和溝渠。

that were there in the past.

事實上，

And in fact,

好奇號探測車已在 火星表面上漫遊 3 年了；

Curiosity --

我們看到它停在一條古老的河床上，

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

在那曾有湍急的水流過，

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

時間不短，

where water flowed rapidly.

可能持續流過數億年之久。

And not for a little while,

如果主要元素都在那裡，

perhaps hundreds of millions of years.

有機物包括在內，

And if everything was there,

也許生命曾誕生過。

including organics,

好奇號在紅土上鑽洞，

perhaps life had started.

挖出了其他的物質。

Curiosity has also drilled in that red soil

我們檢視後，非常地興奮，

and brought up other material.

因為不是紅色，而是灰色的物質：

And we were really excited when we saw that.

灰色的火星。

Because it wasn't red Mars,

把挖出的物質帶回車裡辨識，

it was gray material,

你猜怎麼著？

it's gray Mars.

我們辨識出有機物：

We brought it into the rover,

碳、氫、氧、

we tasted it,

氮、磷、硫，

and guess what?

全都在那裡。

We tasted organics --

所以，過去的火星

carbon, hydrogen, oxygen,

曾有過很多的水，

nitrogen, phosphorus, sulfur --

也許曾有很長的一段時間，

they were all there.

曾有過生命、曾有過生命的火花、

So Mars in its past,

曾有過成長的生命。

with a lot of water,

那時的生命，現在還存在嗎？

perhaps plenty of time,

我們不知道。

could have had life,

但幾年前，

could have had that spark,

我們開始細看一些隕石坑。

could have grown.

在夏季，

And is that life still there?

沿著這些隕石坑的邊緣 會出現深色的條紋。

We don't know that.

我們檢視越多的隕石坑，

But a few years ago

就看到越多這樣的特點，

we started to look at a number of craters.

現在已知超過十二個。

During the summer,

幾個月前，神話成真了。

dark lines would appear down the sides of these craters.

我們向世界宣布 已經知道這些條紋是什麼：

The more we looked,

是液態水。

the more craters we saw,

這些隕石坑在夏天滲流出液體；

the more of these features.

這些液態水流下隕石坑。

We now know more than a dozen of them.

既已發現了水，接下來要做什麼呢？

A few months ago the fairy tale came true.

它告訴了我們，

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

火星具備了組成生命的必要成分，

It's liquid water.

它北半球的三分之二 過去可能有過海洋，

These craters are weeping during the summer.

現在有流下的水。

Liquid water is flowing down these craters.

它的星球表面有液態水。

So what are we going to do now --

它有有機物。

now that we see the water?

它有所有對的條件。

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

那麼，我們接下來要怎麼做呢？

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

我們要展開一系列的任務，

there was an ocean.

開始尋找火星上的生命。

It has weeping water right now.

現在比以往任何時候都更有吸引力。

Liquid water on its surface.

再往更遠的太陽系裡，

It has organics.

我們所看到的是小小的土衛二。

It has all the right conditions.

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。

So what are we going to do next?

這裡距離太陽更遠。

We're going to launch a series of missions

這個衛星，應該是 冰層覆蓋的矽酸鹽核心。

to begin that search for life on Mars.

但我們找到了什麼？

And now it's more appealing than ever before.

自 2006 年起， 卡西尼太空船就在那裡，

As we move out into the solar system,

在飛過了土衛二幾年後再度回顧，

here's the tiny moon Enceladus.

它的發現令我們全都大吃一驚。

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

土衛二往太空噴出羽狀的水，

this area around the sun.

水又落回該衛星上。

This is much further out.

多麼美妙的環境啊。

This object should be ice over a silicate core.

幾個月前卡西尼飛過羽狀物，

But what did we find?

測到矽酸鹽顆粒。

Cassini was there since 2006,

二氧化矽來自何方？

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

一定來自海底。

and surprised us all.

土星產生的潮汐能，

Enceladus is blasting sheets of water out into the solar system

拉扯、擠壓這個衛星，

and sloshing back down onto the moon.

使它的冰層融化，

What a fabulous environment.

形成了海洋；

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

潮汐能同樣也拉扯、擠壓 這衛星的矽酸鹽核心。

and it measured silicate particles.

在地球上，我們想得到 唯一能類比的是

Where does the silica come from?

「海底熱泉。」

It must come from the ocean floor.

海底熱泉於 1977 年 在海洋的深處被發現。

The tidal energy is generated by Saturn,

海洋學家非常地驚訝。

pulling and squeezing this moon --

今天海底有著成千上萬的海底熱泉。

is melting that ice,

我們找到了什麼？

creating an ocean.

海洋學家發現海底熱泉裡，

But it's also doing that to the core.

有著豐饒的生命，

Now, the only thing that we can think of

不管水是酸性或鹼性的，

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

與酸鹼無關。

are hydrothermal vents.

所以，海底熱泉是地球上 生物的極佳住所。

Hydrothermal vents deep in our ocean were discovered in 1977.

那麼土衛二呢？

Oceanographers were completely surprised.

我們相信土衛二因為有水，

And now there are thousands of these below the ocean.

相當長的時間有水，

What do we find?

也相信它有海底熱泉，

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

可能也有有機物存在，

they're teeming with life,

是個可能有生命存在的地方。

regardless of whether the water is acidic or alkaline --

可能不只有微生物， 還有更複雜的生物，

doesn't matter.

因為它有足夠的時間去演化。

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

另一個非常相似的衛星是歐羅巴。

So what about Enceladus?

伽利略號於 1996 年 造訪木星和週邊，

Well, we believe because it has water

好好地觀察了歐羅巴。

and has had it for a significant period of time,

伽利略號任務讓我們得知

and we believe it has hydrothermal vents

歐羅巴的冰殼下有海洋。

with perhaps the right organic material,

以前我們並未看到任何羽狀噴泉，

it is a place where life could exist.

是因為我們那時沒尋找。

And not just microbial --

哈伯太空望遠鏡，

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

在兩年前

Another moon, very similar,

觀察歐羅巴，

is Europa.

看到羽狀噴泉

Galileo visited Jupiter's system in 1996

從南半球的裂縫噴出，

and made fabulous observations of Europa.

就像土衛二那樣。

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

這些衛星

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

不是位於我們傳統認為的宜居區，

But we didn't look for them.

而是在太陽系的外區，

Hubble,

卻有著液態水。

just a couple years ago,

如果那裡存在著有機物，

observing Europa,

就可能有生命。

saw plumes of water

這是個好棒的發現，

spraying from the cracks in the southern hemisphere,

因為這些衛星處在這樣的環境中

just exactly like Enceladus.

已經數十億年。

These moons,

我們認為地球的生命 始於最初的五億年，

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

瞧瞧我們現在的模樣。

that are out in the solar system,

這些衛星真是讓人難以置信。

have liquid water.

另一個我們想要探討的衛星是泰坦。

And if there are organics there,

泰坦是土星的大衛星，

there may be life.

體積可能比水星更大。

This is a fabulous set of discoveries

它有遼闊的大氣層。

because these moons have been in this environment like that

如此遼闊的大氣層，

for billions of years.

主要成份是氮， 加上少量的甲烷和乙烷，

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

必須用雷達穿透才能窺視它。

and look where we are.

卡西尼號在它的地表上發現了液體。

These moons are fabulous moons.

我們看到湖泊，

Another moon that we're looking at is Titan.

某些地方的湖泊幾乎 如我們的黑海一般大，

Titan is a huge moon of Saturn.

湖裡並不是液態水，而是甲烷。

It perhaps is much larger than the planet Mercury.

如果太陽系中存在著一個地方， 那裡的生命跟我們不同，

It has an extensive atmosphere.

是以其它溶劑來代替水──

It's so extensive --

可能是甲烷 ──

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

那地點有可能是泰坦。

that you have to peer through it with radar.

除地球外，太陽系中 還有其他生命存在嗎？

And on the surface, Cassini has found liquid.

我們還不知道，

We see lakes ...

但我們正熱切地追尋著。

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

我們收到的數據真是令人興奮。

And this area is not liquid water;

數據告訴我們、迫使我們

it's methane.

以新的、令人興奮的方式考量。

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

我相信我們正走在正確的軌道上。

where the substitute of water is another solvent --

未來 10 年我們將回答這個問題。

and it could be methane --

如果我們的回答是肯定的，

it could be Titan.

那麼，太陽系中處處有生命。

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

想想看，

We don't know yet,

我們可能並不孤單。

but we're hot on the pursuit.

謝謝。

The data that we're receiving is really exciting

（掌聲）

and telling us --

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

I believe we're on the right track.

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

And if we answer it,

and it's positive,

then life is everywhere in the solar system.

Just think about that.

We may not be alone.

Thank you.

(Applause)