The search for our solar system's ninth planet | Mike Brown

譯者: Lilian Chiu 審譯者: Helen Chang

I'm going to tell you a story from 200 years ago.

讓我跟各位說一個 兩百年前的故事。

In 1820, French astronomer Alexis Bouvard

1820 年，法國天文學家 阿列西布瓦爾

almost became the second person in human history to discover a planet.

幾乎成為人類史上 第二個發現某個行星的人。

He'd been tracking the position of Uranus across the night sky

他一直在用古老的星表 來追蹤天王星在夜空中的位置，

using old star catalogs,

and it didn't quite go around the Sun

天王星並沒有完全依照 他預測的方式繞著太陽轉。

the way that his predictions said it should.

Sometimes it was a little too fast,

有時它會移動太快，

sometimes a little too slow.

有時則是有點太慢。

Bouvard knew that his predictions were perfect.

布瓦爾知道他的預測是完美的。

So it had to be that those old star catalogs were bad.

所以問題一定是出在 那些古老的星表。

He told astronomers of the day,

他告訴那時的天文學家：

"Do better measurements."

「把測量做更好一點。」

So they did.

他們真的做了。

Astronomers spent the next two decades

接下來的二十年，天文學家

meticulously tracking the position of Uranus across the sky,

非常仔細地追蹤天王星 在天空中的位置，

but it still didn't fit Bouvard's predictions.

但仍然不符合布瓦爾的預測。

By 1840, it had become obvious.

到了 1840 年，事實變得很明顯。

The problem was not with those old star catalogs,

那些古老的星表並沒有問題，

the problem was with the predictions.

有問題的是預測。

且天文學家知道原因。

And astronomers knew why.

They realized that there must be a distant, giant planet

他們明白一定有個遙遠、巨大的行星

just beyond the orbit of Uranus

在天王星的軌道外面， 在那軌道上造成牽引力，

that was tugging along at that orbit,

sometimes pulling it along a bit too fast,

造成天王星有時會移動太快，

sometimes holding it back.

有時則會讓它減速。

Must have been frustrating back in 1840

在 1840 年，感覺一定很挫折，

to see these gravitational effects of this distant, giant planet

看得到這個遙遠、巨大的行星 所產生的引力效應，

but not yet know how to actually find it.

卻不知道要怎麼找到它。

相信我，那真的很讓人挫折。

Trust me, it's really frustrating.

(Laughter)

（笑聲）

But in 1846, another French astronomer,

但在 1846 年，另一位 法國天文學家奧本 · 勒維耶，

Urbain Le Verrier,

worked through the math

運用數學計算找出方法 來預測該行星的位置。

and figured out how to predict the location of the planet.

He sent his prediction to the Berlin observatory,

他把他的預測交給柏林天文台，

they opened up their telescope

他們打開了望遠鏡，就在第一晚，

and in the very first night they found this faint point of light

他們發現了一個極微弱的光點， 緩慢地在天空中移動，

slowly moving across the sky

and discovered Neptune.

他們發現了海王星。它和勒維耶 預測的位置只差這麼一點點。

It was this close on the sky to Le Verrier's predicted location.

The story of prediction and discrepancy and new theory

這個做出預測、 發現不一致、提出新理論、

and triumphant discoveries is so classic

成功發現的故事，實在非常經典，

and Le Verrier became so famous from it,

勒維耶也因此成名，

that people tried to get in on the act right away.

讓大家都馬上想要如法炮製。

In the last 163 years,

在過去一百六十三年間，

dozens of astronomers have used some sort of alleged orbital discrepancy

有數十位天文學家用了

某種他們宣稱的不一致，

to predict the existence of some new planet in the solar system.

來預測有某個新的行星 存在於太陽系中。

They have always been wrong.

他們全錯了。

The most famous of these erroneous predictions

這些錯誤預測中最有名的 是帕西瓦爾 · 羅威爾的預測，

came from Percival Lowell,

who was convinced that there must be a planet just beyond Uranus and Neptune,

他深信在天王星和海王星之外 一定還有一個行星

messing with those orbits.

影響那些軌道。

And so when Pluto was discovered in 1930

所以，1930 年羅威爾 天文台發現冥王星時，

at the Lowell Observatory,

everybody assumed that it must be the planet that Lowell had predicted.

大家都假設它一定是 羅威爾預測的那個行星。

They were wrong.

他們錯了。

It turns out, Uranus and Neptune are exactly where they're supposed to be.

結果發現，天王星和海王星的位置 就是它們應該在的位置。

It took 100 years,

花了一百年的時間，

but Bouvard was eventually right.

才證明布瓦爾是對的。

Astronomers needed to do better measurements.

天文學家的確需要 把測量做得更好。

And when they did,

當他們真的做到時，

those better measurements had turned out that

那些更好的測量證明了

there is no planet just beyond the orbit of Uranus and Neptune

並沒有其他行星在天王星 和海王星的軌道之外，

and Pluto is thousands of times too small

冥王星至少還要再大數千倍

to have any effect on those orbits at all.

才有可能影響到那些軌道。

So even though Pluto turned out not to be the planet

所以，雖然後來發現冥王星

並不是原來所想的那個行星，

it was originally thought to be,

it was the first discovery of what is now known to be

但這是第一次發現 我們現在所知的現象：

thousands of tiny, icy objects in orbit beyond the planets.

在行星之外的軌道上 有數以千計的小型、結冰天體。

Here you can see the orbits of Jupiter,

各位在這裡所看到的是木星、

Saturn, Uranus and Neptune,

土星、天王星，和海王星的軌道，

and in that little circle in the very center is the Earth

地球則是在中間的小圓圈裡，

and the Sun and almost everything that you know and love.

那圓圈裡還有太陽 及你所知和所愛的一切。

And those yellow circles at the edge

邊緣上的黃色圓圈

are these icy bodies out beyond the planets.

就是在行星之外的結冰體。

These icy bodies are pushed and pulled

這些結冰體會被行星的 重力場給推開或拉近，

by the gravitational fields of the planets

in entirely predictable ways.

這些移動是完全可以預測的。

Everything goes around the Sun exactly the way it is supposed to.

繞行太陽的所有東西都完全 依照它們應該的方式在繞行。

Almost.

幾乎是所有東西。

So in 2003,

2003 年，

I discovered what was at the time

我發現了當時

the most distant known object in the entire solar system.

在太陽系中最遙遠的已知天體。

It's hard not to look at that lonely body out there

很難不看著遠方那孤獨的 天體，然後說，當然，

and say, oh yeah, sure, so Lowell was wrong,

羅威爾錯了，海王星 之外沒有其他行星，

there was no planet just beyond Neptune,

但這個，這可能是一個新的行星。

but this, this could be a new planet.

The real question we had was,

我們真正要問的是，它繞行 太陽時走的是什麼軌道？

what kind of orbit does it have around the Sun?

Does it go in a circle around the Sun

它是否像行星一樣走圓形的軌道？

like a planet should?

Or is it just a typical member of this icy belt of bodies

或者它只是這結冰體 所形成的冰帶中的一員，

that got a little bit tossed outward and it's now on its way back in?

先前被稍微向外拋出來， 現在它只是在回家的路上？

This is precisely the question

兩百年前在研究天王星時，

the astronomers were trying to answer about Uranus 200 years ago.

天文學家努力想要解答的 也正是這個問題。

They did it by using overlooked observations of Uranus

在發現它的九十一年前， 有許多被忽略的觀察資料，

from 91 years before its discovery

他們的做法就是使用這些資料

to figure out its entire orbit.

來推測出它的整個軌道。

We couldn't go quite that far back,

我們沒有用到那麼早的資料，

but we did find observations of our object from 13 years earlier

但我們確實發現，十三年前 就有這個天體的觀察資料，

that allowed us to figure out how it went around the Sun.

讓我們能想出它如何繞行太陽。

So the question is,

所以，問題是：

它和行星一樣 沿著圓形的軌道繞行太陽？

is it in a circular orbit around the Sun, like a planet,

or is it on its way back in,

或者它和那些結冰體 一樣是在回程途中？

like one of these typical icy bodies?

And the answer is

答案是，

no.

皆非。

It has a massively elongated orbit

它有個非常巨大的細長軌道，

that takes 10,000 years to go around the Sun.

繞行太陽一圓要花一萬年。

We named this object Sedna

我們將這個天體命名為賽德娜， 伊努伊特海洋女神的名字，

after the Inuit goddess of the sea,

in honor of the cold, icy places where it spends all of its time.

它一生都在冰凍的環境中， 這個名字也是在對這項特點致敬。

We now know that Sedna,

現在，我們知道賽德娜的體積 約是冥王星的三分之一，

it's about a third the size of Pluto

and it's a relatively typical member

它是海王星之外的那些結冰體中， 相對比較典型的一個。

of those icy bodies out beyond Neptune.

Relatively typical, except for this bizarre orbit.

相對比較典型， 但不包括它的怪異軌道。

You might look at this orbit and say,

你可能會看著這個軌道，說： 「繞行太陽要一萬年是很怪異。」

"Yeah, that's bizarre, 10,000 years to go around the Sun,"

but that's not really the bizarre part.

但那還不是怪異的部分。

The bizarre part is that in those 10,000 years,

怪異的是，在那一萬年中，

Sedna never comes close to anything else in the solar system.

賽德娜完全不會接近 太陽系中的任何其他東西。

Even at its closest approach to the Sun,

即使在它離太陽最近的點，

Sedna is further from Neptune

賽德娜和海王星的距離 也比海王星和地球的距離更遠。

than Neptune is from the Earth.

If Sedna had had an orbit like this,

如果賽德娜有這樣的軌道，

that kisses the orbit of Neptune once around the Sun,

繞行太陽一圈就會 和海王星的軌道接觸一次，

that would have actually been really easy to explain.

那就會很容易解釋了。

That would have just been an object

那就只是在結冰體的區域中

that had been in a circular orbit around the Sun

以圓形軌道繞行太陽的天體，

in that region of icy bodies,

had gotten a little bit too close to Neptune one time,

有一次太靠近海王星，

and then got slingshot out and is now on its way back in.

因此被彈出去， 現在正在返回的途中。

But Sedna never comes close to anything known in the solar system

但賽德娜從未接近過 太陽系中的任何已知的東西，

that could have given it that slingshot.

不可能造成那樣的彈射。

Neptune can't be responsible,

不會是海王星造成的，

but something had to be responsible.

但總是有成因。

This was the first time since 1845

那是 1845 年之後第一次

that we saw the gravitational effects of something in the outer solar system

我們看到了在外太陽系的 某樣東西產生引力效應，

and didn't know what it was.

卻不知道它是什麼。

I actually thought I knew what the answer was.

我曾經以為我知道答案。

Sure, it could have been some distant, giant planet

的確，

它有可能是外太陽系 一個很遙遠、巨大的行星，

in the outer solar system,

but by this time, that idea was so ridiculous

但，在這個情況中， 這個想法很荒謬，

and had been so thoroughly discredited

且完全不足採信， 所以我並沒有認真看待它。

that I didn't take it very seriously.

But 4.5 billion years ago,

但，四十五億年前，

when the Sun formed in a cocoon of hundreds of other stars,

當太陽在數百個其他 天體的包裹之中形成時，

any one of those stars

那些天體中的任何一個 都有可能太靠近賽德娜，

could have gotten just a little bit too close to Sedna

and perturbed it onto the orbit that it has today.

影響它，讓它進入 現今的這個軌道中。

When that cluster of stars dissipated into the galaxy,

當那群天體消散在銀河中，

the orbit of Sedna would have been left as a fossil record

賽德娜的軌道應該會變成

太陽最早歷史中的化石記錄。

of this earliest history of the Sun.

I was so excited by this idea,

這個想法讓我好興奮，

by the idea that we could look

這表示我們可以去研究 太陽誕生的化石歷史，

at the fossil history of the birth of the Sun,

that I spent the next decade

因此我用接下來十年的時間， 去尋找更多軌道像賽德娜的天體。

looking for more objects with orbits like Sedna.

In that ten-year period, I found zero.

在那十年間，我一個也沒找到。

(Laughter)

（笑聲）

But my colleagues, Chad Trujillo and Scott Sheppard, did a better job,

但我的同事，查德 · 楚基羅 及史考特 · 雪柏都做得比我好，

and they have now found several objects with orbits like Sedna,

他們現在已經找到了好幾個 軌道類似賽德娜的天體，

which is super exciting.

超級讓人興奮。

But what's even more interesting

但，更有趣的是，

is that they found that all these objects

他們發現，所有這些天體

are not only on these distant, elongated orbits,

不僅是在遙遠、細長的軌道上運行，

they also share a common value of this obscure orbital parameter

它們複雜的軌道參數都有相同的值，

that in celestial mechanics we call argument of perihelion.

在天體力學中，我們把這個 參數稱為「近日點輻角」。

When they realized it was clustered in argument of perihelion,

當他們發現這些近日點輻角 都差不多時，馬上手舞足蹈，

they immediately jumped up and down,

認為一定有個遙遠、 巨大的行星存在，

saying it must be caused by a distant, giant planet out there,

這真的很讓人興奮， 只是，完全不合理。

which is really exciting, except it makes no sense at all.

Let me try to explain it to you why with an analogy.

讓我試著用比喻來解釋為什麼。

Imagine a person walking down a plaza

想像一個人走在一個廣場上，

and looking 45 degrees to his right side.

看向他的右邊四十五度方向。

There's a lot of reasons that might happen,

可能有很多理由， 超容易解釋，沒什麼。

it's super easy to explain, no big deal.

現在，想像很多不同的人，

Imagine now many different people,

all walking in different directions across the plaza,

都在廣場上朝不同的方向行走，

but all looking 45 degrees to the direction that they're moving.

但都看向他們行進 方向的四十五度。

Everybody's moving in different directions,

大家行進的方向不同，

everybody's looking in different directions,

大家都看向不同的方向，

but they're all looking 45 degrees to the direction of motion.

但他們看的都是 行進方向的四十五度。

What could cause something like that?

這種現象背後的成因會是什麼？

I have no idea.

我不知道。

It's very difficult to think of any reason that that would happen.

很難想出任何理由 會造成這種現象。

(Laughter)

（笑聲）

And this is essentially what that clustering

基本上，這就是一堆 相近的近日點輻角

in argument of perihelion was telling us.

告訴我們的事。

Scientists were generally baffled and they assumed it must just be a fluke

科學家很受挫，

他們認為一定是僥倖 及不佳的觀察值造成。

and some bad observations.

They told the astronomers,

他們告訴天文學家：

"Do better measurements."

「把測量做更好一點。」

I actually took a very careful look at those measurements, though,

不過，我非常仔細地研究過 這些測量值，它們是對的。

and they were right.

這些天體真的都有同樣的

These objects really did all share

a common value of argument of perihelion,

近日點輻角值，

and they shouldn't.

但不應該如此。

Something had to be causing that.

背後一定有原因。

The final piece of the puzzle came into place in 2016,

拼圖的最後一片在 2016 年出現，

when my colleague, Konstantin Batygin,

康斯坦丁 · 巴蒂金是我的同事，

who works three doors down from me, and I

他的辦公室就在附近，

realized that the reason that everybody was baffled

我明白，大家都受挫的原因

was because argument of perihelion was only part of the story.

是因為近日點輻角 只是故事的一部分。

If you look at these objects the right way,

如果用對的方式來看這些天體，

它們在太空中排成一排， 朝向同樣的方向，

they are all actually lined up in space in the same direction,

and they're all tilted in space in the same direction.

它們在太空中， 都朝同樣的方向傾斜。

It's as if all those people on the plaza are all walking in the same direction

那就好像在廣場上的那些人 都朝同樣的方向行進，

and they're all looking 45 degrees to the right side.

且都看向右邊四十五度。

That's easy to explain.

那就很容易解釋。 他們都在看某樣東西。

They're all looking at something.

These objects in the outer solar system are all reacting to something.

在外太陽系的這些天體 都受到某樣東西影響。

But what?

但，那東西是什麼？

Konstantin and I spent a year

康斯坦丁和我花了一年時間，

trying to come up with any explanation other than a distant, giant planet

想要找出一個不同的解釋，

不是在外太陽系中有個 遙遠、巨大的行星。

in the outer solar system.

We did not want to be the 33rd and 34th people in history to propose this planet

我們並不想要成為 第三十四及三十五位

提出這個行星存在 又被告知弄錯了的人。

to yet again be told we were wrong.

But after a year,

但，一年後，

there was really no choice.

真的沒別的選擇。 我們想不出其他解釋，

We could come up with no other explanation

other than that there is a distant,

唯一的可能就是有個 遙遠、巨大的行星，

massive planet on an elongated orbit,

沿著細長的軌道運行，

inclined to the rest of the solar system,

傾斜向這個太陽系的其他部分，

that is forcing these patterns for these objects

迫使形成這些外太陽系天體的模式。

in the outer solar system.

Guess what else a planet like this does.

猜猜這樣的行星還會做什麼？

Remember that strange orbit of Sedna,

記得賽德娜的奇特軌道嗎？

how it was kind of pulled away from the Sun in one direction?

它好像是被拉離太陽 朝向一個方向行進。

A planet like this would make orbits like that all day long.

這樣的行星會一直產生那樣的軌道。

We knew we were onto something.

我們知道我們有些眉目了。

So this brings us to today.

這就把我們帶到現今。

We are basically 1845, Paris.

基本上，我們是 1845 年的巴黎。

(Laughter)

（笑聲）

We see the gravitational effects of a distant, giant planet,

我們看到遙遠、巨大的行星 造成的引力效應，

and we are trying to work out the calculations

於是我們試著計算出往哪裡尋找，

to tell us where to look, to point our telescopes,

把望遠鏡轉向哪個方向， 才能找到這個行星。

to find this planet.

We've done massive suites of computer simulations,

我們做過大量的電腦模擬，

massive months of analytic calculations

投入無數個月做分析計算，

and here's what I can tell you so far.

目前，我能告訴各位的是：

First, this planet, which we call Planet Nine,

第一，我們把這個行星 稱為第九行星，

because that's what it is,

因為它就是第九個，

Planet Nine is six times the mass of the Earth.

第九行星的質量是地球的六倍。

This is no slightly-smaller-than-Pluto,

這並非「它比冥王星小一點， 還要爭論它是不是行星」的情形。

let's-all-argue-about- whether-it's-a-planet-or-not thing.

這是我們整個太陽系中 第五大的行星。

This is the fifth largest planet in our entire solar system.

For context, let me show you the sizes of the planets.

為了說明起見，先讓各位 看一下這些行星的大小。

In the back there, you can the massive Jupiter and Saturn.

在後面，可以看到 巨大的木星和土星。

Next to them, a little bit smaller, Uranus and Neptune.

在它們旁邊的是天王星 和海王星，比較小一點。

Up in the corner, the terrestrial planets, Mercury, Venus, Earth and Mars.

在上面角落的是類地行星， 水星、金星、地球、火星。

You can even see that belt

甚至可以看到海王星外面的 結冰體帶，冥王星也是其中一員，

of icy bodies beyond Neptune, of which Pluto is a member,

good luck figuring out which one it is.

猜猜是哪一個，祝好運。

And here is Planet Nine.

這是第九行星。

Planet Nine is big.

第九行星很大。

Planet Nine is so big,

第九行星大到你應該要納悶 我們為什麼還沒找到它。

you should probably wonder why haven't we found it yet.

Well, Planet Nine is big,

嗯，第九行星很大， 但它也非常非常遠。

but it's also really, really far away.

It's something like 15 times further away than Neptune.

它的所在可能比海王星 還要遠十五倍。

And that makes it about 50,000 times fainter than Neptune.

那就表示它比海王星 還要微弱五萬倍。

And also, the sky is a really big place.

此外，天空真的很大。

We've narrowed down where we think it is

我們已經把它可能的所在範圍縮小 成天空中相對很小的一塊區域，

to a relatively small area of the sky,

but it would still take us years

但我們仍然要花數年的時間

to systematically cover the area of the sky

才能系統性地找完 天空中的那個區域，

with the large telescopes that we need

還得使用很大的望遠鏡

to see something that's this far away and this faint.

才能夠看到那麼遙遠、 那麼微弱的行星。

Luckily, we might not have to.

幸運的是，我們可能不用這麼做。

Just like Bouvard used unrecognized observations of Uranus

就像布瓦爾使用

當時仍未被發現的天王星

from 91 years before its discovery,

之前 91 年的資料，

I bet that there are unrecognized images

我敢說一定有些未被承認的影像

that show the location of Planet Nine.

可以顯示出第九行星的位置。

It's going to be a massive computational undertaking

這勢必要用到非常大量的計算，

to go through all of the old data

才能分析完所有的舊資料，

and pick out that one faint moving planet.

並挑出那一個微弱的移動行星。

But we're underway.

但我們在進行了。

And I think we're getting close.

我認為我們快成功了。

So I would say, get ready.

所以，我要說的是，準備好。

We are not going to match Le Verrier's

我們比不上勒維耶的

"make a prediction,

「做一個預測，

have the planet found in a single night

一個晚上就在離預測位置 不遠處找到行星」的記錄。

that close to where you predicted it" record.

But I do bet that within the next couple of years

但我敢說，在接下來幾年內，

some astronomer somewhere

某地的某個天文學家

will find a faint point of light,

會發現有一個微弱的光點

slowly moving across the sky

緩慢地在天空中移動，

and triumphantly announce the discovery of a new,

並洋洋得意地宣佈 他真的在我們的太陽系中

and quite possibly not the last,

發現了一個新的行星， 且很可能還有其他的行星存在。

real planet of our solar system.

Thank you.

謝謝。

(Applause)

（掌聲）