Where did the Moon come from? A new theory | Sarah T. Stewart

譯者: Lilian Chiu 審譯者: Bruce Sung

（掌聲）

Nobody likes to make a mistake.

沒有人喜歡犯錯。

And I made a whopping one.

而我犯了個超級大錯。

And figuring out what I did wrong led to a discovery

我找出了我做錯什麼， 後續導致了一個發現，

that completely changes the way we think about the Earth and Moon.

完全改變了我們對於 地球和月球的看法。

I'm a planetary scientist,

我是行星科學家，

and my favorite thing to do is smash planets together.

我最愛做的事情就是 把行星撞在一起。

(Laughter)

（笑聲）

In my lab, I can shoot at rocks using cannons like this one.

在我的實驗室，我可以用 像這樣的大砲對岩石開火。

(Cannon shot)

（大砲開火）

(Laughter)

（笑聲）

In my experiments, I can generate the extreme conditions

依我的經驗，我可以產生出

在行星形成時的極端條件。

during planet formation.

And with computer models, I can collide whole planets together

用電腦模型，我可以 讓行星整個相撞，

to make them grow,

讓它們長大，

or I can destroy them.

或是我也可以摧毀它們。

(Laughter)

（笑聲）

I want to understand how to make the Earth and the Moon

我想要了解，如何能 製造出地球和月球，

and why the Earth is so different from other planets.

以及為什麼地球 和其他行星如此不同。

The leading idea for the origin of the Earth and Moon

關於地球和月球最初 如何形成的主要想法是

is called the "giant impact theory."

所謂的「大碰撞說」。

The theory states that a Mars-sized body struck the young Earth,

這個理論是火星大小的天體 撞擊了年輕的地球，

and the Moon formed from the debris disk around the planet.

而月球是從該行星的盤狀分佈 碎片殘駭所形成。

The theory can explain so many things about the Moon,

這個理論能解釋許多月球的狀況，

but it has a huge flaw:

但它有個巨大的瑕疵：

it predicts that the Moon is mostly made from the Mars-sized planet,

它預測，月球的主要成分 是那個火星大小的行星，

that the Earth and the Moon are made from different materials.

所以地球和月球是用 不同的材料生成的。

But that's not what we see.

但，我們看到的並非如此。

The Earth and the Moon are actually like identical twins.

地球和月球其實像是同卵雙胞胎。

The genetic code of planets is written in the isotopes of the elements.

行星的基因碼是寫在 元素的同位素中。

The Earth and Moon have identical isotopes.

地球和月球有相同的同位素。

That means that the Earth and Moon are made from the same materials.

那就表示，地球和月球 是用同樣的材料生成的。

It's really strange that the Earth and the Moon are twins.

地球和月球是雙胞胎， 這是很奇怪的事。

All of the planets are made from different materials,

所有的行星都是由 不同的材料生成的，

so they all have different isotopes,

所以它們都有不同的同位素，

they all have their own genetic code.

它們都有自己的基因碼。

No other planetary bodies have the same genetic relationship.

沒有任何其他行星體 有相同的基因關係。

Only the Earth and Moon are twins.

只有地球和月球是雙胞胎。

When I started working on the origin of the Moon,

當我開始研究月球的起源時，

there were scientists that wanted to reject the whole idea of the giant impact.

有些科學家想要推翻 整個大碰撞說。

They didn't see any way for this theory to explain the special relationship

他們不認為這個理論能夠解釋

地球和月球之間的特殊關係。

between the Earth and the Moon.

We were all trying to think of new ideas.

我們都在試圖提出新的想法。

The problem was, there weren't any better ideas.

問題是，沒有其他更好的想法。

All of the other ideas had even bigger flaws.

所有其他想法都有更大的瑕疵。

So we were trying to rescue the giant impact theory.

所以，我們在試圖拯救大碰撞說。

A young scientist in my group suggested that we try changing the spin

我的團隊中有一位 年輕的科學家建議，

我們可以試著改變 大碰撞說的自轉。

of the giant impact.

Maybe making the Earth spin faster could mix more material

也許讓地球自轉速度更快， 就能混合更多材料，

and explain the Moon.

並能解釋月球的形成。

The Mars-sized impactor had been chosen

撞擊地球的火星大小行星 已經被選定，

because it could make the Moon

因為它可以形成月球，

and make the length of Earth's day.

並形成地球白天時間的長度。

People really liked that part of the model.

大家真的很喜歡模型的這個部分。

But what if something else determined the length of Earth's day?

但，如果地球的白天時間長度 是由其他因素決定的呢？

Then there would be many more possible giant impacts that could make the Moon.

那麼，就會有更多大碰撞 都有可能形成月球。

I was curious about what could happen,

我很好奇可能發生的狀況，

so I tried simulating faster-spinning giant impacts,

所以我試著模擬 自轉更快速的大碰撞，

and I found that it is possible

我發現，的確有可能

to make a disk out of the same mixture of materials as the planet.

用這個行星的材料組合 來生成一個盤。

We were pretty excited.

我們相當興奮。

Maybe this was the way to explain the Moon.

也許這種方式就能解釋月球。

The problem is, we also found that that's just not very likely.

問題是，我們也發現， 這實在不太可能發生。

Most of the time, the disk is different from the planet,

通常，生成的盤 都和這個星球不同，

and it looked like making our Moon this way

看起來，若要用這種方式 生成我們的月球，

would be an astronomical coincidence,

那會是天文學上的巧合，

and it was just hard for everyone to accept the idea

大家很難接受

that the Moon's special connection to Earth was an accident.

月球和地球的特殊關聯只是個意外。

The giant impact theory was still in trouble,

大碰撞理論仍然在困境中，

and we were still trying to figure out how to make the Moon.

我們仍然在試圖想出 月球是怎麼生成的。

Then came the day when I realized my mistake.

接著，有一天，我發現了我的錯誤。

My student and I were looking at the data from these fast-spinning giant impacts.

我和我的學生在看 快速自轉大碰撞的資料。

On that day, we weren't actually thinking about the Moon,

那天，我們其實 並沒有在想月球的問題，

we were looking at the planet.

我們是在看那個行星。

The planet gets super-hot and partially vaporized

因為撞擊的能量， 那個星球變得超級熱，

from the energy of the impact.

且有部分已經蒸發。

But the data didn't look like a planet.

但那資料看起來並不像個行星。

It looked really strange.

它看起來相當奇怪。

The planet was weirdly connected to the disk.

這個行星和盤有著奇怪的連結。

I got that super-excited feeling

我有種超興奮的感覺，

when something really wrong might be something really interesting.

當有非常不對勁的狀況時， 可能會有很有趣的發現。

In all of my calculations,

在我所有的計算中，

I had assumed there was a planet with a separate disk around it.

我都假設有一個行星， 它周圍有一個分開的盤。

Calculating what was in the disk as how we tested

我們測試碰撞是否能夠 生成月球的方式，

whether an impact could make the Moon.

就是計算那個盤中有什麼。

But it didn't look that simple anymore.

但，看起來不再是那麼簡單了。

We were making the mistake

我們犯的錯

of thinking that a planet was always going to look like a planet.

是認為行星看起來 一定會是行星的樣子。

On that day, I knew that a giant impact was making something completely new.

那天，我知道

大碰撞產生出來的是全新的東西。

I've had eureka moments.

我有過靈光一現的時刻。

This was not one of them.

這個時刻並非其中之一。（笑聲）

(Laughter)

I really didn't know what was going on.

我真的不知道到底怎麼回事。

I had this strange, new object in front of me

我前面有著這個奇怪的新物體，

and the challenge to try and figure it out.

面對著要試圖搞懂它的挑戰。

What do you do when faced with the unknown?

當你面對未知時，該怎麼做？

How do you even start?

到底要如何開始？

We questioned everything:

我們質疑一切：

What is a planet?

什麼是行星？

When is a planet no longer a planet anymore?

何時行星不再算是行星？

We played with new ideas.

我們開始玩新的想法。

We had to get rid of our old way of thinking,

我們得要擺脫過去的思考方式，

and by playing, I could throw away all of the data,

透過「玩」，我可以 丟掉所有的資料、

all of the rules of the real world,

真實世界中的所有規則，

and free my mind to explore.

解放我的大腦，讓它去探索。

And by making a mental space

我製造了一個心智空間，

where I could try out outrageous ideas

在那裡，我可以嘗試 無法無天的想法，

and then bring them back into the real world to test them,

接著把這些想法 帶回真實世界做測試，

I could learn.

我能學習。

And by playing, we learned so much.

透過「玩」，我們學了好多。

I combined my lab experiments with computer models

我把我的實驗室實驗 和電腦模型結合，

and discovered that after most giant impacts,

發現在大部分大碰撞之後，

the Earth is so hot, there's no surface.

地球都非常熱，熱到沒有表面。

There's just a deep layer of gas that gets denser and denser with depth.

只有一層很深層的氣體， 越深的地方密度越高。

The Earth would have been like Jupiter.

地球本來可能像木星一樣。

There's nothing to stand on.

沒有立足之地。

And that was just part of the problem.

那只是問題的一部分。

I wanted to understand the whole problem.

我想要了解整個問題。

I couldn't let go of the challenge to figure out what was really going on

我無法放手這個挑戰，我想要想通

在大碰撞中到底發生了什麼事。

in giant impacts.

It took almost two years

花了近兩年時間，

of throwing away old ideas

不斷把舊想法丟棄，

and building new ones

建立新想法，

that we understood the data

我們才了解了那些資料，

and knew what it meant for the Moon.

搞懂那對月球的意涵是什麼。

I discovered a new type of astronomical object.

我發現了一種新的天文物體。

It's not a planet.

它不是行星。

It's made from planets.

它是由行星生成的。

A planet is a body whose self-gravity

行星是一個天體，它自己的重力

is strong enough to give it its rounded shape.

強到可以讓它形成圓形的形狀。

It spins around all together.

它會形成一個整體一起自轉。

Make it hotter and spin it faster,

若讓它更熱，自轉更快，

the equator gets bigger and bigger until it reaches a tipping point.

赤道就會越來越大， 直到達到臨界點。

Push past the tipping point,

若超過了臨界點，

and the material at the equator spreads into a disk.

赤道的材料會散佈成盤狀。

It's now broken all the rules of being a planet.

現在，它就打破了 所有身為行星的規則。

It can't spin around together anymore,

它不再能整體一起自轉了。

its shape keeps changing as it gets bigger and bigger;

隨著它越長越大， 它的形狀不斷改變；

the planet has become something new.

這個行星變成了某種新東西。

We gave our discovery its name:

我們把這項發現命名為：

synestia.

索內斯蒂亞（synestia）。

We named it after the goddess Hestia,

我們採用的是女神 Hestia 的名字，

the Greek goddess of the hearth and home,

掌管爐灶和家庭的希臘女神，

because we think the Earth became one.

因為我們認為地球 變成了這樣的角色。

The prefix means "all together,"

字首 syn 意思是「全部一起」， 強調所有材料之間的連結。

to emphasize the connection between all of the material.

A synestia is what a planet becomes

當高熱與自轉速度將一個行星 推過了圓球形的極限時，

when heat and spin push it over the limit of a spheroidal shape.

它就變成了索內斯蒂亞。

Would you like to see a synestia?

你們想要看看索內斯蒂亞嗎？

(Cheers)

（歡呼）

In this visualization of one of my simulations,

這裡透過視覺呈現出來的 是我的其中一項模擬，

the young Earth is already spinning quickly from a previous giant impact.

年輕的地球已經因為 先前的大碰撞而在快速自轉，

Its shape is deformed, but our planet would be recognizable

它的形狀變形了，但仍然 可以認出這是我們的星球，

by the water on its surface.

因為它的表面有水。

The energy from the impact vaporizes the surface,

碰撞的能量讓蒸發了地表、

the water, the atmosphere,

水、大氣，

and mixes all of the gases together in just a few hours.

只花了幾個小時的時間 就把所有的氣體混合在一起。

We discovered that many giant impacts make synestias,

我們發現，許多大碰撞 會產生索內斯蒂亞，

but these burning, bright objects don't live very long.

但這些燃燒、明亮的物體 沒有很長的生命。

They cool down, shrink and turn back into planets.

它們會冷卻、縮小，轉變回行星。

While rocky planets like Earth were growing,

當像地球這種岩石行星在成長時，

they probably turned into synestias one or more times.

可能會有一次或數次 轉變為索內斯蒂亞。

A synestia gives us a new way to solve the problem of the origin of the Moon.

索內斯蒂亞讓我們有了一個新方法 可以解決月球起源的問題。

We propose that the Moon formed inside a huge, vaporous synestia.

我們提出，

月球是在一個大型、 蒸汽的索內斯蒂亞中形成的。

The Moon grew from magma rain

岩石蒸汽濃縮成岩漿雨，

that condensed out of the rock vapor.

月球則從岩漿雨中生成。

The Moon's special connection to Earth

月球和地球的連結會如此特殊，

is because the Moon formed inside the Earth

是因為月球在地球內部形成，

when Earth was a synestia.

當時地球是個索內斯蒂亞。

The Moon could have orbited inside the synestia for years,

月球有可能在這個索內斯蒂亞 內部運行了很多年，

hidden from view.

這時是看不見的。

The Moon is revealed by the synestia cooling and shrinking

當索內斯蒂亞在月球軌道 內部冷卻並縮小時，

inside of its orbit.

月球就顯現出來了。

The synestia turns into planet Earth

這個索內斯蒂亞再經過 數百年的冷卻之後，

only after cooling for hundreds of years longer.

就轉變成了地球。

In our new theory,

在我們的新理論中，

the giant impact makes a synestia,

大碰撞造成了一個索內斯蒂亞，

and the synestia divides into two new bodies,

而這個索內斯蒂亞 分開成了兩個新天體，

creating our isotopically identical Earth and Moon.

創造出我們的地球和月球， 且讓它們擁有相同的同位素。

Synestias have been created throughout the universe.

在宇宙各處都有 索內斯蒂亞被創造出來。

And we only just realized that by finding them in our imagination:

我們會了解這件事，是因為 我們在我們的想像中找到它們：

What else am I missing in the world around me?

在我周遭的世界中， 我還遺漏了什麼？

What is hidden from my view by my own assumptions?

有什麼是被我自己的假設 給遮蔽了，讓我無法看見？

The next time you look at the Moon,

下次當你抬頭看月亮時，

remember:

別忘了：

the things you think you know

你認為你知道的事，

may be the opportunity to discover something truly amazing.

也許會是發現驚人新事物的機會。

(Applause)

（掌聲）