in one stroke, thousands of textbooks were out of date.

才一瞬間，幾千本教科書都得淘汰

In my role as Public Astronomer here in Greenwich, I'm always being asked about Pluto.

我擔任格林威治這裡的公眾天文學家，一直有人問我冥王星

Why was it reclassified?

為什麼把它重新歸類？

And if it's not a planet anymore, then what on earth can it be?

如果它不再是行星，又會是什麼？

Right from its discovery, Pluto seemed different from the other planets.

自從發現冥王星，它似乎就和其他行星不太一樣

Here at the Royal Observatory, we have records going back for hundreds of years,

在皇家天文台這裡，我們有紀錄可追溯至幾百年前

and somewhere, we should have a record of the discovery of Pluto.

這裡應該有發現冥王星的紀錄

1917, that's too early... 1987, much too late.

1917年，太早了…1987年又太晚

Clyde Tombaugh had been set the specific task of finding a planet,

克萊德·湯博被指派發現行星這項特殊任務

so when he saw his moving point of light in 1930, what else was he going to think he'd found?

所以他在1930年看到移動的光點時，還能想到他發現了什麼？

Here we have the President, Council, and Fellows at the Royal Astronomical Society sending the Lowell Observatory

在這裡，英國皇家天文學會的會長、議會、會員都向洛厄爾天文台送上

their heartiest congratulations on the great discovery of the Trans-Neptunian planet.

衷心的祝賀，於海王星之外行星的偉大發現

But trouble was brewing from the word go.

但問題馬上浮現

Within weeks, Pluto's status was being called into question.

幾週之內，冥王星的地位遭受質疑

Its eccentric orbit and small mass set it apart from the other planets.

它古怪的運行軌道和過小的質量，顯得與其他行星不同

More importantly, some scientists argued that Pluto might not be alone.

更重要的是，許多科學家認為冥王星不是個案

Over the decades, our ideas about the formation of the Solar System developed.

幾十年過後，我們對太陽系構成的想法有了發展

It was suggested that the edge of the dust and gas cloud from which our planets formed

一般來說，行星的形成是來自塵粒和氣體的星雲的邊緣

would have been too spread out to condense into planets.

星雲散開，壓縮成了行星

Instead, they could be something very different.

不然會變成迥然不同的天體

Scientists reasoned that there could be hundreds of thousands of icy objects on the edge of the solar system

科學家推論在太陽系的邊緣，會有數十萬個冰狀天體

that had failed to be incorporated into one of the major planets.

都無法合併形成行星

They called this region the Kuiper Belt,

他們稱那個區域為「庫伯帶」

and Pluto's status as a planet started to be called into question.

冥王星作為行星的地位便開始令人懷疑

On the fifth of January, 2005, came the fatal blow.

2005 年 1 月 5 日，帶來致命打擊

Scientists in California discovered another small moving point of light.

科學家在加州發現另一個移動的小光點

This was Eris, a world they believed was bigger than Pluto.

這是鬩神星，他們相信它比冥王星來得大

This was huge news.

這可是重大消息

The likelihood was, there could be many more large objects out there.

可能那裡還會有許多更大的天體

Scientists were faced with a choice: either open the doors to potentially hundreds of new planets,

科學家面臨抉擇：是要讓潛在的數百顆天體都視為新的行星

or Pluto was for the chop.

還是把冥王星排除在外

In 2006, the International Astronomical Union put it to the vote,

2006年，國際天文學聯合會投票表決

and it wasn't good news for Pluto.

對冥王星而言並非好消息

The IAU decided that a planet had to be an object in orbit around the sun,

國際天文學聯合會決議出行星必須是軌道圍繞著太陽的天體

that was massive enough for gravity to squeeze it into a spherical shape,

它有巨大的引力足以擠成球體

but also it had to be gravitationally dominant,

還得主宰周遭的引力

and that meant it must have cleared its surrounding region of other similarly sized objects,

意思就是，它得清除附近區域中，其他大小相似的天體

but with everything else out there in the Kuiper Belt, this was Pluto's downfall.

但庫伯帶還存有各種相似的天體，導致冥王星被除名

So where did this leave Pluto?

那冥王星成了什麼？

The IAU decided to classify it as a dwarf planet.

國際天文學聯合會決定將它列為矮行星

To many, this would seem as a demotion, but I'm not so sure.

不少人認為冥王星被降級，但我不那麼確信

As a planet, it was the last gasp on the edge of the Solar System,

冥王星是太陽系邊際行星的最後一搏

but now it's an exciting example of a brand new class of objects.

現在，對於全新的天體分類，有了令人振奮的先例

Whatever we learn from it will change the way we think about our corner of the galaxy.

不論我們從中得知什麼，都將改變我們對銀河冰山一隅的想法