Fred Jansen: How to land on a comet

譯者: Quan Sun 審譯者: Seke Wei

I'd like to take you on the epic quest of the Rosetta spacecraft.

我將帶領大家跟著羅塞塔號太空船 進行史詩般的探險。

To escort and land the probe on a comet,

護送這個探測器在一顆彗星上登陸，

this has been my passion for the past two years.

一直是我這過去兩年來的熱情所在。

In order to do that,

為此，

I need to explain to you something about the origin of the solar system.

我需要向大家解釋一些關於太陽系起源的東西。

When we go back four and a half billion years,

讓我們回到45億年前，

there was a cloud of gas and dust.

有個充滿氣體和灰塵的雲團。

In the center of this cloud, our sun formed and ignited.

在這個雲團的中心， 我們的太陽在那裡形成並燃燒。

Along with that, what we now know as planets, comets and asteroids formed.

同時，今日所知的行星、彗星和小行星跟著形成。

What then happened, according to theory,

根據理論，接下來，

is that when the Earth had cooled down a bit after its formation,

隨著地球形成並逐漸冷卻，

comets massively impacted the Earth and delivered water to Earth.

大量彗星撞擊地球，並帶來了水。

They probably also delivered complex organic material to Earth,

它們可能還給地球帶來了複雜的有機物。

and that may have bootstrapped the emergence of life.

正是這些有機物引發了生命的出現。

You can compare this to having to solve a 250-piece puzzle

這過程猶如必須拼湊一幅250片的拼圖，

and not a 2,000-piece puzzle.

而非2000片。

Afterwards, the big planets like Jupiter and Saturn,

之後，像木星和土星之類的大行星，

they were not in their place where they are now,

它們尚未在今日所在位置，

and they interacted gravitationally,

透過彼此重力吸引，

and they swept the whole interior of the solar system clean,

它們將整個內太陽系空間清掃乾淨。

and what we now know as comets

至於今日所知之彗星，

ended up in something called the Kuiper Belt,

最後則落入所謂柯伊伯帶之內。

which is a belt of objects beyond the orbit of Neptune.

這是一條位於海王星軌道之外的天體聚集帶。

And sometimes these objects run into each other,

有時這些天體會相互碰撞，

and they gravitationally deflect,

導致引力偏向，

and then the gravity of Jupiter pulls them back into the solar system.

此時，木星的引力會將它們拉回太陽系。

And they then become the comets as we see them in the sky.

然後，它們就變成我們在天空中所見的彗星。

The important thing here to note is that in the meantime,

重要的一點是，在此期間，

the four and a half billion years,

在這45億年間，

these comets have been sitting on the outside of the solar system,

這些彗星一直安坐於太陽系之外，

and haven't changed --

並且從沒變過——

deep, frozen versions of our solar system.

就像沉底，凍結版的太陽系。

In the sky, they look like this.

在天空中，它們看起來像這樣。

We know them for their tails.

我們靠慧尾認識它們，

There are actually two tails.

慧尾其實有兩條。

One is a dust tail, which is blown away by the solar wind.

一條是塵埃尾，因太陽風吹拂而生。

The other one is an ion tail, which is charged particles,

另一條是離子尾，含帶電粒子，

and they follow the magnetic field in the solar system.

其方向遵循太陽系內磁場方向。

There's the coma,

這是慧髮，

and then there is the nucleus, which here is too small to see,

然後這是慧核，小到看不見，

and you have to remember that in the case of Rosetta,

但是別忘記，就羅塞塔號而言，

the spacecraft is in that center pixel.

太空船就在中央那個像素裡。

We are only 20, 30, 40 kilometers away from the comet.

我們距離彗星只有20 、30、 40公里。

So what's important to remember?

其重要性何在？

Comets contain the original material from which our solar system was formed,

彗星中含有太陽系形成時的原始物質，

so they're ideal to study the components

因此，其成份是我們研究地球

that were present at the time when Earth, and life, started.

及生命起源時期的絕佳對象。

Comets are also suspected

彗星還疑似

of having brought the elements which may have bootstrapped life.

帶來了那些引發生命起源的元素。

In 1983, ESA set up its long-term Horizon 2000 program,

1983年，歐洲太空總署(ESA) 開啟了長期的地平線2000計畫，

which contained one cornerstone, which would be a mission to a comet.

其中包含一塊重要基石，即彗星探索任務。

In parallel, a small mission to a comet, what you see here, Giotto, was launched,

同時期，為了一項小型的彗星探索任務， 畫面上的喬托號發射升空，

and in 1986, flew by the comet of Halley with an armada of other spacecraft.

喬托號於1986年飛掠過哈雷彗星， 前後跟著一大群其他太空船。

From the results of that mission, it became immediately clear

通過那次任務的結果，一件事變得很清楚，

that comets were ideal bodies to study to understand our solar system.

那就是彗星是用來研究太陽系的理想天體。

And thus, the Rosetta mission was approved in 1993,

因此，1993年批准了羅塞塔號任務，

and originally it was supposed to be launched in 2003,

一開始，它應該是在2003年發射的，

but a problem arose with an Ariane rocket.

卻因亞利安火箭出現問題而取消。

However, our P.R. department, in its enthusiasm,

不過，我們的公關部門，充滿熱情，

had already made 1,000 Delft Blue plates

他們早已製作了1000枚代爾夫特藍陶盤，

with the name of the wrong comets.

並印上了那些錯誤的彗星名字。

So I've never had to buy any china since. That's the positive part.

因此從那以後我就不需再買任何瓷器。 這也算是其正向的一面。

(Laughter)

（笑聲）

Once the whole problem was solved,

解決了所有問題之後，

we left Earth in 2004

羅塞塔號於2004年離開地球，

to the newly selected comet, Churyumov-Gerasimenko.

飛向重新選定的丘留莫夫·格拉西緬科彗星。

This comet had to be specially selected

這顆彗星是特別挑選的，

because A, you have to be able to get to it,

因為首先，你必須能到得了，

and B, it shouldn't have been in the solar system too long.

其次，它必須沒在太陽系長期待過。

This particular comet has been in the solar system since 1959.

這顆特別的彗星從1959年開始來到太陽系。

That's the first time when it was deflected by Jupiter,

那是它受木星偏向後第一次來到太陽系，

and it got close enough to the sun to start changing.

且靠近太陽近到足夠出現變化。

So it's a very fresh comet.

所以這是一顆非常新的彗星。

Rosetta made a few historic firsts.

羅塞塔號取得了好些歷史性的第一。

It's the first satellite to orbit a comet,

它是首顆環繞彗星的人造衛星，

and to escort it throughout its whole tour through the solar system --

並跟著慧星周遊整個太陽系——

closest approach to the sun, as we will see in August,

八月將到達近日點，

and then away again to the exterior.

然後離開太陽系。

It's the first ever landing on a comet.

這是首次有太空船在彗星上登陸。

We actually orbit the comet using something which is not

在環繞這顆彗星飛行時，我們實際用到一項

normally done with spacecraft.

其他太空船罕用的技術。

Normally, you look at the sky and you know where you point and where you are.

通常，你望向天空，就能知道你的方位和座標。

In this case, that's not enough.

但是為了環繞慧星，那還不夠。

We navigated by looking at landmarks on the comet.

我們要靠彗星上的地標來導航。

We recognized features -- boulders, craters --

我們辨別一些特徵——卵石、坑洞——

and that's how we know where we are respective to the comet.

這樣才能知道我們相對於彗星的位置。

And, of course, it's the first satellite to go beyond the orbit of Jupiter

當然，這也是使用太陽能電池的太空船

on solar cells.

第一次飛越木星的軌道。

Now, this sounds more heroic than it actually is,

這聽起來似乎是項英雄事蹟，但事實不完全如此，

because the technology to use radio isotope thermal generators

理由是那時候歐洲還沒有 放射性同位素熱電源的技術可用，

wasn't available in Europe at that time, so there was no choice.

所以當時別無選擇。

But these solar arrays are big.

不過這些太陽能電池板很大。

This is one wing, and these are not specially selected small people.

這是它的一隻翅膀，而這些是人， 沒有特意挑矮子。

They're just like you and me.

他們是跟你我一樣的正常人。

(Laughter)

（笑聲）

We have two of these wings, 65 square meters.

我們有兩隻翅膀，共65平方公尺。

Now later on, of course, when we got to the comet,

當然，隨後當我們到達這顆彗星時，

you find out that 65 square meters of sail

你會發現，讓這65平方公尺的巨帆

close to a body which is outgassing is not always a very handy choice.

向一個正在釋放氣體的天體靠近並不是很方便的設計。

Now, how did we get to the comet?

我們是怎麼到達這顆彗星呢？

Because we had to go there for the Rosetta scientific objectives

因為我們須要到一個十分遙遠的地方 去完成羅塞塔號的

very far away -- four times the distance of the Earth to the sun --

科學任務——距離為地球到太陽的4倍——

and also at a much higher velocity than we could achieve with fuel,

而且須要以一個遠超過我們用燃料 所能達到的速度飛行。

because we'd have to take six times as much fuel as the whole spacecraft weighed.

如果要達到這速度， 我們得攜帶六倍於太空船本身重量的燃料。

So what do you do?

所以你會怎麼做？

You use gravitational flybys, slingshots,

你會採用重力場飛掠法，即彈弓原理，

where you pass by a planet at very low altitude,

以非常低的高度，飛掠行星，

a few thousand kilometers,

大概幾千公里高，

and then you get the velocity of that planet around the sun for free.

這樣你就能免費獲得那顆行星的公轉速度。

We did that a few times.

我們這樣做了好多次。

We did Earth, we did Mars, we did twice Earth again,

我們利用過地球、火星 ，然後又第二次使用地球，

and we also flew by two asteroids, Lutetia and Steins.

我們還飛掠了兩顆小行星，司琴星，以及斯坦斯。

Then in 2011, we got so far from the sun that if the spacecraft got into trouble,

然後到了2011年，我們已經距離太陽夠遠了， 如果這時太空船遇到什麼問題，

we couldn't actually save the spacecraft anymore,

事實上，我們再也沒辦法拯救它了，

so we went into hibernation.

所以我們進入冬眠狀態。

Everything was switched off except for one clock.

除了一個時鐘外，所有其他儀器都關掉了。

Here you see in white the trajectory, and the way this works.

畫面上白線為太空船的運動軌跡， 可看出其工作原理。

You see that from the circle where we started,

你看，從一開始出發的這個圓，

the white line, actually you get more and more and more elliptical,

沿著白線，我們看到軌跡變成越來越狹長的橢圓，

and then finally we approached the comet

2014年5月，我們終於靠近彗星。

in May 2014, and we had to start doing the rendezvous maneuvers.

然後我們開始進行會合動作。

On the way there, we flew by Earth and we took a few pictures to test our cameras.

在途中，我們飛經地球 並拍了一些照片以測試我們的相機。

This is the moon rising over Earth,

這是月球從地平線上升的景像，

and this is what we now call a selfie,

這是我們現在所稱的自拍，

which at that time, by the way, that word didn't exist. (Laughter)

順便說一下，那個時候“自拍” 這個詞還不存在。（笑聲）

It's at Mars. It was taken by the CIVA camera.

這是在火星上方， 由彗星紅外與可見光分析儀 (CIVA) 相機所拍攝。

That's one of the cameras on the lander,

那是登陸器上的一台相機，

and it just looks under the solar arrays,

從太陽能電池板下方望出的景像，

and you see the planet Mars and the solar array in the distance.

你能看到火星及遠處的太陽能電池板。

Now, when we got out of hibernation in January 2014,

當我們在2014年1月從冬眠中甦醒後，

we started arriving at a distance

5月份我們到達距離慧星

of two million kilometers from the comet in May.

200萬公里的地方。

However, the velocity the spacecraft had was much too fast.

然而，這時太空船的速度太快了。

We were going 2,800 kilometers an hour faster than the comet, so we had to brake.

我們的時速比這顆彗星快2800 公里， 因此我們需要刹一刹車。

We had to do eight maneuvers,

我們作了8次的減速動作，

and you see here, some of them were really big.

你看這圖，其中的一些減速幅度真的很大。

We had to brake the first one by a few hundred kilometers per hour,

我們的第一次減速需要將時速降低數百公里，

and actually, the duration of that was seven hours,

這個過程實際花了7個小時，

and it used 218 kilos of fuel,

並消耗了218公斤燃料，

and those were seven nerve-wracking hours, because in 2007,

這7小時令人心驚膽戰，因為在2007年，

there was a leak in the system of the propulsion of Rosetta,

羅塞塔號的推進系統出現了漏氣現象，

and we had to close off a branch,

使得我們必須關掉一處分路，

so the system was actually operating at a pressure

因此推進系統實際所處的工作壓力

which it was never designed or qualified for.

並不符合原始設計條件。

Then we got in the vicinity of the comet, and these were the first pictures we saw.

然後我們到達這顆彗星的附近， 這是我們看到的第一批照片。

The true comet rotation period is 12 and a half hours,

這顆彗星真實的自轉週期是12.5小时，

so this is accelerated,

所以這是加快影片，

but you will understand that our flight dynamics engineers thought,

但是你會理解我們的飛行動力學工程師在想什麼，

this is not going to be an easy thing to land on.

這可不是一個容易登陸的東西。

We had hoped for some kind of spud-like thing

我們原本希望它像某種馬鈴薯形狀一樣

where you could easily land.

可以輕易的登陸在上面。

But we had one hope: maybe it was smooth.

我們還有一種希望：也許它是平坦的。

No. That didn't work either. (Laughter)

不，以上兩種都不是。（笑聲）

So at that point in time, it was clearly unavoidable:

因此，當下顯然別無選擇：

we had to map this body in all the detail you could get,

我們得儘可能詳細繪製這個天體的地圖，

because we had to find an area which is 500 meters in diameter and flat.

因為我們必須找到一塊直徑500公尺的平地。

Why 500 meters? That's the error we have on landing the probe.

為什麼是500公尺？ 這是我們探測器登陸時的誤差。

So we went through this process, and we mapped the comet.

我們經歷此過程，繪製出彗星表面的地圖。

We used a technique called photoclinometry.

我們使用一種叫做照相測斜術的技術。

You use shadows thrown by the sun.

作法是利用太陽拋下的陰影。

What you see here is a rock sitting on the surface of the comet,

你在這裡看到一塊安坐於彗星表面的岩石，

and the sun shines from above.

陽光從上面照下來。

From the shadow, we, with our brain,

透過陰影，我們用大腦，

can immediately determine roughly what the shape of that rock is.

可以立刻大致判斷出這塊岩石的形狀。

You can program that in a computer,

這過程可以用電腦寫成程式，

you then cover the whole comet, and you can map the comet.

然後將範圍涵蓋整顆彗星， 你就可以繪製彗星地圖。

For that, we flew special trajectories starting in August.

為此，我們從8月份開始以一種特殊的軌跡飛行。

First, a triangle of 100 kilometers on a side

首先，在100公里距離的地方，

at 100 kilometers' distance,

沿一個邊長為100公里的三角形飛行，

and we repeated the whole thing at 50 kilometers.

然後將距離及邊長改為50公里再重複整個過程。

At that time, we had seen the comet at all kinds of angles,

此時，我們已從各種角度觀察過這顆彗星，

and we could use this technique to map the whole thing.

可利用本技術繪製彗星全圖。

Now, this led to a selection of landing sites.

現在，到了選擇登陸地點的時候了。

This whole process we had to do, to go from the mapping of the comet

這整個必要過程，從繪製彗星地圖，

to actually finding the final landing site, was 60 days.

到實際找到最終登陸地點，花費60天。

We didn't have more.

我們並沒有更多的時間。

To give you an idea, the average Mars mission

給你們一個參考，平均一次火星任務

takes hundreds of scientists for years to meet

需要上百位科學家花數年的時間開會

about where shall we go?

才能找到一個登陸地點。

We had 60 days, and that was it.

我們只有60天，就那麼多了。

We finally selected the final landing site

我們最終選定了一個登陸點，

and the commands were prepared for Rosetta to launch Philae.

並且為羅塞塔號準備好發射菲萊號的指令。

The way this works is that Rosetta has to be at the right point in space,

其登陸方式為羅塞塔號得處在太空中的正確位置，

and aiming towards the comet, because the lander is passive.

並且瞄準這顆彗星，因為登陸器是被動的。

The lander is then pushed out and moves towards the comet.

隨後推出登陸器，使其飛向彗星。

Rosetta had to turn around

羅塞塔號得轉個身，

to get its cameras to actually look at Philae while it was departing

讓其相機正對著菲萊號飛離過程，

and to be able to communicate with it.

及維持通訊。

Now, the landing duration of the whole trajectory was seven hours.

整個登陸過程花費7個小時。

Now do a simple calculation:

簡單的計算一下：

if the velocity of Rosetta is off by one centimeter per second,

如果羅塞塔號的速度誤差是每秒1公分，

seven hours is 25,000 seconds.

7個小時就是25000秒，

That means 252 meters wrong on the comet.

那就意味著登陸器登陸彗星時的誤差是252公尺。

So we had to know the velocity of Rosetta

因此羅塞塔號的速度誤差

much better than one centimeter per second,

必須小於每秒1公分，

and its location in space better than 100 meters

其太空中的位置誤差必須小於100公尺

at 500 million kilometers from Earth.

此時它距離地球5億公里遠。

That's no mean feat.

那可不容易。

Let me quickly take you through some of the science and the instruments.

讓我快速帶領大家認識一些科學和儀器。

I won't bore you with all the details of all the instruments,

我不會講太多儀器細節，以免大家厭煩，

but it's got everything.

但是它什麼東西都有。

We can sniff gas, we can measure dust particles,

我們可以聞氣體，可以測塵粒，

the shape of them, the composition,

測量其形狀及成份，

there are magnetometers, everything.

有磁力儀，等等一切。

This is one of the results from an instrument which measures gas density

這是一部儀器所測到的氣體密度結果

at the position of Rosetta,

位置在羅塞塔號附近，

so it's gas which has left the comet.

所以這是從彗星上釋放出來的氣體。

The bottom graph is September of last year.

這下面的圖是去年9月份的結果。

There is a long-term variation, which in itself is not surprising,

可看到一個長期的變化，這變化本身並不稀奇，

but you see the sharp peaks.

但是你看那些尖峰。

This is a comet day.

這就是彗星上的一天。

You can see the effect of the sun on the evaporation of gas

你可以看到太陽影響氣體蒸發的效果，

and the fact that the comet is rotating.

以及彗星本身旋轉的事實。

So there is one spot, apparently,

所以顯然有一處地點，

where there is a lot of stuff coming from,

很多東西都出自那裡，

it gets heated in the Sun, and then cools down on the back side.

它受太陽加熱，然後在背面冷卻。

And we can see the density variations of this.

我們可以看看這裡的密度差異。

These are the gases and the organic compounds

這些是我們已經測量到的

that we already have measured.

氣體和有機化合物。

You will see it's an impressive list,

這是一張令人印象深刻的清單，

and there is much, much, much more to come,

以後還會有更多更多的東西出現在上面，

because there are more measurements.

因為還會作更多測量。

Actually, there is a conference going on in Houston at the moment

其實，目前在休斯頓那邊就有一場研討會，

where many of these results are presented.

許多結果正在發表。

Also, we measured dust particles.

還有，我們也測量塵粒。

Now, for you, this will not look very impressive,

現在對你們來說可能毫不起眼，

but the scientists were thrilled when they saw this.

但是當科學家們看到這個的時候都非常激動。

Two dust particles:

畫面有兩顆塵粒：

the right one they call Boris, and they shot it with tantalum

右邊的塵粒它們叫伯里斯，他們用鉭去撞擊它，

in order to be able to analyze it.

以便能夠分析它。

Now, we found sodium and magnesium.

我們發現了鈉和鎂。

What this tells you is this is the concentration of these two materials

這顯示出太陽系形成時期，

at the time the solar system was formed,

這兩種物質的濃度。

so we learned things about which materials were there

所以我們學到行星形成時，

when the planet was made.

存在哪些物質。

Of course, one of the important elements is the imaging.

當然，重要設備之一就是相機。

This is one of the cameras of Rosetta, the OSIRIS camera,

這是羅塞塔號上的一部相機——OSIRIS (光學、光譜與紅外遙測攝影系統) 相機——所拍攝，

and this actually was the cover of Science magazine

其實這曾是《科學》雜誌

on January 23 of this year.

今年1月23日那一期的封面。

Nobody had expected this body to look like this.

沒有人想到這天體會看來如此。

Boulders, rocks -- if anything, it looks more like the Half Dome in Yosemite

大卵石，岩石——如果非要和其他地方作比較，

than anything else.

它看起來更像是優勝美地的半圓丘。

We also saw things like this:

我們還看到了這樣的東西：

dunes, and what look to be, on the righthand side, wind-blown shadows.

沙丘，及右手邊， 看起來好像受風吹動的影子。

Now we know these from Mars, but this comet doesn't have an atmosphere,

目前我們知道火星上有這些，但是這顆彗星沒有大氣，

so it's a bit difficult to create a wind-blown shadow.

所以要產生一個受風吹動的影子是有點困難的。

It may be local outgassing,

這可能是局部氣體釋放，

stuff which goes up and comes back.

有什麼東西上升然後落下來。

We don't know, so there is a lot to investigate.

我們還不清楚，所以還有很多需要調查。

Here, you see the same image twice.

這裡，你看到同一地點的兩張照片。

On the left-hand side, you see in the middle a pit.

左手邊這張，你看中間有一個坑。

On the right-hand side, if you carefully look,

右手邊這張，如果你仔細看，

there are three jets coming out of the bottom of that pit.

有三股氣流從那個坑的底部噴出。

So this is the activity of the comet.

這就是這顆彗星的活動。

Apparently, at the bottom of these pits is where the active regions are,

顯然，這些坑的底部就是活動區域，

and where the material evaporates into space.

也是物質蒸發到太空的地方。

There is a very intriguing crack in the neck of the comet.

這顆彗星的頸部有一條非常引人好奇的裂縫。

You see it on the right-hand side.

你可以從右手邊照片看到。

It's a kilometer long, and it's two and a half meters wide.

它有1公里長，2.5公尺寬。

Some people suggest that actually,

事實上有些人暗示，

when we get close to the sun,

隨著我們靠近太陽，

the comet may split in two,

這顆彗星可能一分為二，

and then we'll have to choose,

這時我們將必須選擇，

which comet do we go for?

究竟要跟隨哪一半彗星？

The lander -- again, lots of instruments,

這是（菲萊號）登陸器——一樣的，攜帶了很多儀器，

mostly comparable except for the things which hammer in the ground and drill, etc.

除了地面錘子和鑽子等，幾乎可與羅塞塔號相媲美。

But much the same as Rosetta, and that is because you want to compare

而與羅塞塔號攜帶幾乎一樣的儀器是因為我們想比較

what you find in space with what you find on the comet.

來自太空和來自彗星上的兩種觀察結果有何不同。

These are called ground truth measurements.

這些稱為“地面真值調查”。

These are the landing descent images

這些是登陸下降照片

that were taken by the OSIRIS camera.

由OSIRIS相機拍攝。

You see the lander getting further and further away from Rosetta.

你看登陸器離羅塞塔號越來越遠。

On the top right, you see an image taken at 60 meters by the lander,

右上角，是登陸器在60公尺高拍的照片，

60 meters above the surface of the comet.

彗星表面60公尺上空。

The boulder there is some 10 meters.

那個大卵石直徑約10米。

So this is one of the last images we took before we landed on the comet.

這是我們登陸彗星前所拍的最後一張照片。

Here, you see the whole sequence again, but from a different perspective,

這裡，我們從一個不同的視角將整個過程再看一遍，

and you see three blown-ups from the bottom-left to the middle

從圖左下角到中間有三幅放大照，

of the lander traveling over the surface of the comet.

顯示登陸器飛過彗星表面的情景。

Then, at the top, there is a before and an after image of the landing.

然後，在頂部有登陸之前和登陸之後的對比照片。

The only problem with the after image is, there is no lander.

其中，登陸後的照片有個問題就是找不到登陸器。

But if you carefully look at the right-hand side of this image,

但是你如果仔細觀察這張照片的右手邊，

we saw the lander still there, but it had bounced.

我們看到登陸器還在，只是它彈走了。

It had departed again.

它又離開了彗星表面。

Now, on a bit of a comical note here

現在，有點滑稽的是

is that originally Rosetta was designed to have a lander which would bounce.

本來在羅塞塔號的設計中， 它會攜帶一個能反彈的登陸器。

That was discarded because it was way too expensive.

但是因為成本太高所以這一方案遭捨棄。

Now, we forgot, but the lander knew.

現在，我們忘了這件事，但是登陸器還記得。

(Laughter)

（笑聲）

During the first bounce, in the magnetometers,

第一次反彈期間，在磁力儀上，

you see here the data from them, from the three axes, x, y and z.

你可以看到來自X、Y、Z三個座標軸的資料。

Halfway through, you see a red line.

半途中，你可以看到一條紅線。

At that red line, there is a change.

在紅線處，有發生改變。

What happened, apparently, is during the first bounce,

發生了什麼？很顯然在第一次反彈時

somewhere, we hit the edge of a crater with one of the legs of the lander,

登陸器的一條腿在某處碰到一個坑的邊緣，

而登陸器的旋轉速度產生改變。

and the rotation velocity of the lander changed.

So we've been rather lucky

所以我們能落在目前所在位置，

that we are where we are.

是非常幸運的。

This is one of the iconic images of Rosetta.

這是羅塞塔號拍的標誌性圖片之一。

It's a man-made object, a leg of the lander,

那是一個人造物體，登陸器的腿，

standing on a comet.

站在一顆彗星上。

This, for me, is one of the very best images of space science I have ever seen.

對我來說，這是所見太空科學照片中最棒的一張。

(Applause)

（掌聲）

One of the things we still have to do is to actually find the lander.

我們仍然需要去做的一件事是實際找到這個登陸器。

The blue area here is where we know it must be.

藍色區域是我們認為它應在的位置。

We haven't been able to find it yet, but the search is continuing,

我們還沒能找到它，但是搜索仍在繼續，

as are our efforts to start getting the lander to work again.

同時我們也在努力讓登陸器重新工作。

We listen every day,

我們每天用心監聽，

and we hope that between now and somewhere in April,

我們希望從現在到4月份的某個時候，

the lander will wake up again.

這個登陸器會再一次醒來。

The findings of what we found on the comet:

我們在這顆彗星上的發現有：

This thing would float in water.

這個東西可以在水上漂浮。

It's half the density of water.

其密度為水的一半。

So it looks like a very big rock, but it's not.

因此它看起來雖然像一個很大的岩石， 但實際上不是。

The activity increase we saw in June, July, August last year

去年6、7、8月我們看到

was a four-fold activity increase.

其活躍性提高了4倍。

By the time we will be at the sun,

當我們靠近太陽時，

there will be 100 kilos a second leaving this comet:

每秒將會有100公斤的物質離開這顆彗星：

gas, dust, whatever.

氣體、灰塵等。

That's 100 million kilos a day.

1天的話就是1億公斤。

Then, finally, the landing day.

最後，結束前，要提登陸那一天。

I will never forget -- absolute madness, 250 TV crews in Germany.

我將永生難忘——太瘋狂了， 在德國有250名電視臺工作人員在場。

The BBC was interviewing me,

當BBC採訪我時，

and another TV crew who was following me all day

旁邊還有一位電視臺工作人員，整天跟著我，

were filming me being interviewed,

也同時在拍攝我的訪問過程，

and it went on like that for the whole day.

那種狀況持續了一整天。

The Discovery Channel crew

探索頻道的工作人員

actually caught me when leaving the control room,

在離開控制室時找到了我，

and they asked the right question,

他們問了個好問題，

and man, I got into tears, and I still feel this.

我竟哭了起來，我現在仍然能感受到這心情。

For a month and a half,

此後的1個半月裡，

I couldn't think about landing day without crying,

每次想到登陸日我都會熱淚盈眶，

and I still have the emotion in me.

那種情緒仍留存在我心裡。

With this image of the comet, I would like to leave you.

我想用這張彗星照片來結束今天的演講。

Thank you.

謝謝。

(Applause)

（掌聲）