And it's a journey that you and I have been on for many years now,

在接下來的18分鐘裡，我將帶大家去旅行。

and it began some 50 years ago, when humans first stepped off our planet.

我們的旅程已經經歷很多年了，

And in those 50 years, not only did we literally, physically set foot on the moon,

50年前，人類第一次涉足外太空時，這段旅程便開始了。

but we have dispatched robotic spacecraft to all the planets -- all eight of them --

在這50年裡，我們不僅成功地登上了月球，

and we have landed on asteroids, we have rendezvoused with comets,

還把太空船發射到了太陽系中的八大行星上

and, at this point in time, we have a spacecraft on its way to Pluto,

我們在隕星上著陸，與彗星相遇，

the body formerly known as a planet.

現在這一刻，我們有一架太空飛船正向冥王星駛去，

And all of these robotic missions are part of a bigger human journey:

飛向這顆曾被認為是行星的星球。

a voyage to understand something, to get a sense of our cosmic place,

所有這些機械裝置的出使任務都是為了將來實現載人航空。

to understand something of our origins, and how Earth, our planet,

它們幫助我們了解宇宙，

and we, living on it, came to be.

了解我們的本源，了解我們的家園地球，

And of all the places in the solar system that we might go to

過去的狀態，

and search for answers to questions like this,

了解太陽系中所有我們想去的地方，

there's Saturn. And we have been to Saturn before --

找到所有類似問題的答案。

we visited Saturn in the early 1980s --

這是土星。我們曾經到過土星。

but our investigations of Saturn have become far more in-depth in detail

1980年代早期我們探訪過土星。

since the Cassini spacecraft, traveling across interplanetary space

而現在，我們對土星的研究比當時更加深入、仔細。

for seven years, glided into orbit around Saturn in the summer of 2004,

卡西尼號太空飛船穿梭於行星之間

and became at that point the farthest robotic outpost

長達七年之久，它2004年駛入土星運行軌道，

that humanity had ever established around the Sun.

成為當時人類發射到太陽系中

Now, the Saturn system is a rich planetary system.

距離地球最遠的機械裝置。

It offers mystery, scientific insight and obviously splendor beyond compare,

現在，土星是一個龐大而複雜的行星系統。

and the investigation of this system has enormous cosmic reach.

它是如此神祕，充滿了無與倫比的科學研究價值，

In fact, just studying the rings alone, we stand to learn a lot

這個系統的勘察，對宇宙學的發展擁有極其深遠的意義。

about the discs of stars and gas that we call the spiral galaxies.

實際上，單是從土星的光環中我們就能學到很多

And here's a beautiful picture of the Andromeda Nebula,

關於星星可視圓面和旋渦星雲的知識。

which is our closest, largest spiral galaxy to the Milky Way.

這裡有一張仙女星雲的照片，非常漂亮，

And then, here's a beautiful composite of the Whirlpool Galaxy,

這是離銀河系最近，體積最大的旋渦星系。

taken by the Hubble Space Telescope.

這是渦狀星系，它的構造異常美麗。

So the journey back to Saturn is really part of and is also a metaphor

這是由哈勃太空望遠鏡所拍攝的。

for a much larger human voyage

飛往土星的這段旅程真是 -- 一個形象的比喻 --

to understand the interconnectedness of everything around us,

是人類漫長探索之旅的重要部份。

and also how humans fit into that picture.

我們通過探索去了解身邊事物之間的聯繫，

And it pains me that I can't tell you all that we have learned with Cassini.

了解人類為何存在。

I can't show you all the beautiful pictures that we've taken

我很愧疚，在過去的兩年半時間裡，我因為太忙了，

in the last two and a half years, because I simply don't have the time.

而沒有向大家展示我們通過卡西尼號探測器收集的信息

So I'm going to concentrate on two of the most exciting stories

和所有我們拍攝到的無比壯觀的圖片。

that have emerged out of this major exploratory expedition

下面我會講一講這次長達兩年的探索土星之旅，

that we are conducting around Saturn,

我想重點講這次重大探索之旅中

and have been for the past two and a half years.

發生的兩件

Saturn is accompanied by a very large and diverse collection of moons.

最令人心潮澎湃的事情。

They range in size from a few kilometers across to as big across as the U.S.

陪伴在土星周圍的是眾多體積龐大，形狀各異的衛星。

Most of the beautiful pictures we've taken of Saturn, in fact,

有些衛星的直徑有幾公里，而有些衛星的直徑可以橫跨整個美國。

show Saturn in accompaniment with some of its moons. Here's Saturn with Dione,

我們拍攝到的這些土星美圖基本上

and then, here's Saturn showing the rings edge-on,

都有土星和圍繞著它的衛星。這是土星和土衛四戴奧妮，

showing you just how vertically thin they are, with the moon Enceladus.

這是土衛二和土星最外圍的光環，

Now, two of the 47 moons that Saturn has are standouts.

從縱向看，它們有多薄。

And those are Titan and Enceladus. Titan is Saturn's largest moon,

在土星47顆衛星中，有兩顆特別耀眼。

and, until Cassini had arrived there,

它們分別是土衛六泰坦和土衛二恩克拉多斯。泰坦是土星最大的衛星，

was the largest single expanse of unexplored terrain

在卡西尼號到達之前，

that we had remaining in our solar system.

它是我們在太陽系中最大的，

And it is a body that has long intrigued people who've watched the planets.

未經勘探的單獨地帶。

It has a very large, thick atmosphere,

它是長期以來研究這些行星的人們朝思暮想的一塊寶地。

and in fact, its surface environment was believed to be

它的大氣層非常厚，

more like the environment we have here on the Earth,

事實上，它的地表環境被認為是

or at least had in the past, than any other body in the solar system.

接近於地球上的環境。

Its atmosphere is largely molecular nitrogen, like you are breathing here in this room,

至少在過去，人們認為它比其它太陽系中的天體更接近。

except that its atmosphere is suffused with

它的大氣中含有大量氮分子，就跟你們在這裡吸入的氮氣一樣，

simple organic materials like methane and propane and ethane.

只不過裡面有過量

And these molecules high up in the atmosphere of Titan

簡單有機物

get broken down, and their products join together to make haze particles.

這些氣體分子散佈在土衛六大氣的頂層，

This haze is ubiquitous. It's completely global and enveloping Titan.

分解之後，它們的產物化合成霧狀顆粒。

And that's why you cannot see down to the surface

這些霧狀物四處擴散，把土衛六完全包裹起來。

with our eyes in the visible region of the spectrum.

所以單憑我們的肉眼視力，

But these haze particles, it was surmised,

根本無法看清它的表面。

before we got there with Cassini, over billions and billions of years,

但是在卡西尼號到達之前，我們推測，這些霧狀顆粒

gently drifted down to the surface and coated the surface

經過上千億年的時間

in a thick organic sludge.

一點一點積聚並覆蓋在土衛六表面

So like the equivalent, the Titan equivalent, of tar, or oil, or what -- we didn't know what.

形成一層有機的泥狀物。

But this is what we suspected. And these molecules,

就像泰坦上的焦油，油，或者類似的甚麼東西 -- 我們當時無法確定。

especially methane and ethane, can be liquids at the surface temperatures of Titan.

這是我們的推測。而這些分子，

And so it turns out that methane is to Titan what water is to the Earth.

尤其是甲烷和乙烷，它們在泰坦的地表溫度下會呈現液態。

It's a condensable in the atmosphere,

結果發現，甲烷在土衛六上呈現出的狀態，就好跟水在地球上的狀態一樣，

and so recognizing this circumstance brought to the fore

它在大氣中是會冷凝的，

a whole world of bizarre possibilities. You can have methane clouds, OK,

所以認識到這種情況的存在之後，

and above those clouds, you have this hundreds of kilometers of haze,

我們就有了千奇百怪的設想。可能那裡存在甲烷做的雲，是吧，

which prevent any sunlight from getting to the surface.

在這些雲之上，幾十萬米厚的霧狀顆粒層

The temperature at the surface is some 350 degrees below zero Fahrenheit.

遮擋住了陽光，使它無法到達地表。

But despite that cold, you could have rain falling down on the surface of Titan.

地表的溫度為華氏零下350度(約攝氏零下212度)。

And doing on Titan what rain does on the Earth: it carves gullies; it forms rivers

即使在這樣的低溫下，土衛六上還是會出現降水。

and cataracts; it can create canyons; it can pool in large basins and craters.

這些降水像地球上的雨水一樣，使地表形成溝渠，河流

It can wash the sludge off high mountain peaks and hills,

以及瀑布。它還能形成峽谷，大型盆地，以及凹地。

down into the lowlands. So stop and think for a minute.

它能把泥狀物從高山丘陵上

Try to imagine what the surface of Titan might look like.

沖到低窪地帶。我們停下來想一想。

It's dark. High noon on Titan is as dark as deep earth twilight on the Earth.

想像土衛六的地表是甚麼樣子的。

It's cold, it's eerie, it's misty,

那裡一片黑暗 -- 土衛六上的中午時刻跟地球上黎明來臨之前一樣黑暗。

it might be raining, and you might be standing

那裡天寒地凍，陰森恐怖，迷霧重重，

on the shores of Lake Michigan brimming with paint thinner. (Laughter)

那裡可能正在下雨，而你可能正站在

That is the view that we had of the surface of Titan before we got there with Cassini,

氾濫著塗料稀釋劑（成份為甲烷）的密歇根湖邊。

and I can tell you that what we have found on Titan, though it is not the same in detail,

這是我們在卡西尼號到達土衛六之前的遐想，

is every bit as fascinating as that story is.

我可以告訴大家，我們真正在土衛六上發現的，跟我們的想像不盡相同，

And for us, it has been like -- the Cassini people --

但是卻一樣引人入勝。

it has been like a Jules Verne adventure come true.

對於我們，也就卡西尼號的工作人員而言，

As I said, it has a thick, extensive atmosphere.

這段旅程就像是儒勒·凡爾納（《八十天環遊世界》作者）的小說在現實中上演。

This is a picture of Titan, backlit by the Sun, with the rings as a beautiful backdrop.

我剛才說過，它有很厚的一層大氣。

And yet another moon there --

這張照片是土衛六在被對太陽時被拍下來的，它的光環構成了一幅壯麗的背景。

I don't even know which one it is. It's a very extensive atmosphere.

而那裡是另一顆衛星 --

We have instruments on Cassini which can see down to the surface

我都不知道究竟是哪一顆。這是個擴散得很開的大氣層。

through this atmosphere, and my camera system is one of them.

在卡西尼號上有專門儀器能夠幫助我們透過大氣層

And we have taken pictures like this.

看到土衛六地表，我的成像科學子系統就是儀器之一。

And what you see is bright and dark regions, and that's about as far as it got for us.

我們拍下了這些照片。

It was so mystifying: we couldn't make out what we were seeing on Titan.

你看到的是明於暗的地帶，這是儀器能拍到的最近距離。

When you look closer at this region, you start to see things

那裡霧太大了 -- 我們無法確定看到的是甚麼。

like sinuous channels -- we didn't know. You see a few round things.

當你湊近了看那塊區域，你可以看到一些物體，

This, we later found out, is, in fact, a crater,

形狀像委蛇的溝渠，不知道是甚麼。還可以看到一些圓形圖案。

but there are very few craters on the surface of Titan,

後來我們發現，這原來是一個殞坑，

meaning it's a very young surface.

但是，土衛六表面的殞坑數量很少，

And there are features that look tectonic.

這說明土衛六的地表非常年輕。

They look like they've been pulled apart.

上面有一些像是由地殻運動產生的地表特徵。

Whenever you see anything linear on a planet,

地表像是被外力撕裂了一般。

it means there's been a fracture, like a fault.

如果你看到行星表面的一些線形圖案，

And so it's been tectonically altered.

那就是地表的裂隙，比如一個斷層。

But we couldn't make sense of our images,

也就是說土衛六發生過地殻運動。

until, six months after we got into orbit,

但是我們還是無法解讀這些圖像，

an event occurred that many have regarded

直到我們進入軌道六個月之後，

as the highlight of Cassini's investigation of Titan.

一件重大事件發生了。它後來被許多人譽為

And that was the deployment of the Huygens probe,

卡西尼號突探測土衛六的突出成就。

the European-built Huygens probe that Cassini had carried

這就是惠更斯號探測器的成功發射。

for seven years across the solar system. We deployed it to the atmosphere of Titan,

這個探測器在歐洲被研製出來，乘著卡西尼號

it took two and a half hours to descend, and it landed on the surface.

在浩瀚的太陽系里穿梭了七年。我們把它發射到土衛六的大氣中，

And I just want to emphasize how significant an event this is.

兩個半小時之後，它在地表著陸。

This is a device of human making,

我真想強調一下這一行動的重大意義。

and it landed in the outer solar system for the first time in human history.

這是人類歷史上第一次有人造的機器

It is so significant that, in my mind,

在外太陽系的天體上登陸。

this was an event that should have been celebrated

在我心目中，它實在是意義非凡，

with ticker tape parades in every city across the U.S. and Europe,

我們值得為它

and sadly, that wasn't the case.

在美國，歐洲的大街小巷敲鑼打鼓，舉行盛大遊行，

(Laughter).

真遺憾，這沒有得到響應。

It was significant for another reason. This is an international mission,

（眾人笑）

and this event was celebrated in Europe, in Germany,

另一個顯示其重大意義的理由是，這是一項國際合作項目，

and the celebratory presentations were given in English accents,

在德國，人們為此事舉行了歡慶活動，

and American accents, and German accents, and French and Italian and Dutch accents.

慶典節目的表演者有英國人，

It was a moving demonstration of what the words

美國人，德國人，法國人，義大利人，和荷蘭人。

"united nations" are supposed to mean:

這是在用行動來詮釋

a true union of nations joined together in a colossal effort for good.

“聯合國”一詞的真諦：

And, in this case, it was a massive undertaking to explore a planet,

國家之間真誠團結協作，眾志成城。

and to come to understand a planetary system

探測一顆遙不可及的星球

that, for all of human history, had been unreachable,

並試圖了解一個星球的體系

and now humans had actually touched it.

需要耗費龐大的人力物力。

So it was -- I mean, I'm getting goose bumps just talking about it.

而現在，人類終於到達了這樣一個星球。

It was a tremendously emotional event,

這真是 -- 我只是說一下，就開始起雞皮疙瘩了，

and it's something that I will personally never forget, and you shouldn't either.

這的確是激動人心的一件事，

(Applause).

它讓我永生難忘，你們也應該有同感。

But anyway, the probe took measurements of the atmosphere on the way down,

（眾人鼓掌）

and it also took panoramic pictures.

探測器在降落過程中對大氣進行了測量，

And I can't tell you what it was like to see the first pictures

並且拍攝了全景照片。

of Titan's surface from the probe. And this is what we saw.

我無法用言語來表達第一次看到土衛六地表照片時

And it was a shocker, because it was everything we wanted

我的心情有多麼激動。這是我們看到的景象。

those other pictures taken from orbit to be.

太令人震驚了，這些從土星軌道上拍攝的景象

It was an unambiguous pattern, a geological pattern.

和我們的設想正好吻合。

It's a dendritic drainage pattern that can be formed only by the flow of liquids.

地表呈現出清晰的幾何圖案。

And you can follow these channels

它所呈現出的樹枝狀水流圖案，肯定是因液體的流動而形成的。

and you can see how they all converge.

你可以沿著這些溝渠

And they converge into this channel here, which drains into this region.

找到它們的匯合點。

You are looking at a shoreline.

它們匯聚到這條溝里，從這裡滲透到地下。

Was this a shoreline of fluids? We didn't know.

你們看到的是一條海岸線。

But this is somewhat of a shoreline.

這是液體的海岸線嗎？我們不知道。

This picture is taken at 16 kilometers.

但是，這肯定是一條海岸線。

This is the picture taken at eight kilometers, OK? Again, the shoreline.

這是在離地表16公里的高度所拍攝的照片。

Okay, now, 16 kilometers, eight kilometers -- this is roughly an airline altitude.

這張是在8公里的高度拍攝的。看，還是那條海岸線。

If you were going to take an airplane trip across the U.S.,

好，16公里，8公里 -- 大概就是普通飛機的飛行高度。

you would be flying at these altitudes.

如果你乘飛機橫跨美國，

So, this is the picture you would have at the window of Titanian Airlines

這就相當於你的飛行高度。

as you fly across the surface of Titan. (Laughter)

假如你正乘坐著土衛六航空公司的飛機俯瞰土衛六，

And then finally, the probe came to rest on the surface,

你看到的就是這副景象。（眾人笑）

and I'm going to show you, ladies and gentlemen,

最後，探測器在地面著陸。

the first picture ever taken from the surface of a moon in the outer solar system.

女士們，先生們，下面我為你們展示

And here is the horizon, OK?

首張外太陽系衛星表面的照片。

These are probably water ice pebbles, yes?

這裡是地平線，看見了嗎？

(Applause).

這些很可能是冰鵝卵石。

And obviously, it landed in one of these flat, dark regions

（眾人鼓掌）

and it didn't sink out of sight. So it wasn't fluid that we landed in.

很明顯，它落在了其中一塊平坦的陰影地帶。

What the probe came down in was basically

它沒有沉沒消失，這說明它沒有落在液體上。

the Titan equivalent of a mud flat.

實際上，它降落的地點

This is an unconsolidated ground that is suffused with liquid methane.

類似於一灘淤泥。

And it's probably the case that this material

這是液態甲烷形成的半流體。

has washed off the highlands of Titan

形成這種地貌的原因可能是

through these channels that we saw,

液態甲烷順著我們剛才看到的那些溝渠

and has drained over billions of years to fill in low-lying basins.

沖蝕了土衛六上的高地，

And that is what the Huygens probe landed in.

滲透並填充到低窪地帶長達幾十億年的時間。

But still, there was no sign in our images,

這就是惠更斯號探測器著陸的地方。

or even in the Huygens' images, of any large, open bodies of fluids.

然而，我們還是沒有看到我們之前預想的

Where were they? It got even more puzzling when we found dunes.

或者惠更斯號圖片上顯示的大面積液體。

OK, so this is our movie of the equatorial region of Titan,

都在哪裡呢？當我們看到一些沙丘時，我們就更加困惑了。

showing these dunes. These are dunes that are 100 meters tall,

這里是土衛六赤道地帶的錄像，

separated by a few kilometers,

這些就是上面的沙丘。它們高達100米，

and they go on for miles and miles and miles.

之間相隔幾公里遠，

There's hundreds, up to a 1,000 or 1,200 miles of dunes.

延綿數千英里。

This is the Saharan desert of Titan.

這些沙丘帶短則幾百英里，長則1000到1200英里。

It's obviously a place which is very dry, or you wouldn't get dunes.

這簡直就相當於土衛六的撒哈拉沙漠。

So again, it got puzzling that there were no bodies of fluid,

顯然，這裡非常乾燥，否則不會有沙丘。

until finally, we saw lakes in the polar regions.

這讓人更加懷疑這裡是否有液態物存在，

And there is a lake scene in the south polar region of Titan.

直到我們最後看到了極地的湖泊。

It's about the size of Lake Ontario.

這是土衛六南極的一個湖。

And then, only a week and a half ago,

它的大小相當於安大略湖。

we flew over the north pole of Titan and found, again,

接著，也就一個多星期以後，

we found a feature here the size of the Caspian Sea.

我們飛過北極，

So it seems that the liquids, for some reason we don't understand,

發現了相當於加勒比海大小的一片區域。

or during at least this season, are apparently at the poles of Titan.

不知為何，可能是這個季節的原因，土衛六上的液體，

And I think you would agree that we have found Titan

都出現在極地地帶。

is a remarkable, mystical place. It's exotic, it's alien, but yet strangely Earth-like,

相信你們應該會同意，土衛六是一個

and having Earth-like geological formations

不可思議的地方。它是那麼特別，那麼遙遠，但又和地球有著驚人的相似處。

and a tremendous geographical diversity,

它有著像類似地球表面的地貌

and is a fascinating world whose only rival in the solar system

和豐富的地質多樣性。