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Pluto, the Un-Planet?

ROBERT SIEGEL, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

If you have a little model of the solar system at home, you can break off the outermost planet. Astronomers today gave Pluto the heave ho, voting in an official definition for the word planet that leaves Pluto out. The term planet has been around since Ancient Greece, but coming to consensus on a precise definition today proved challenging, even for the world's top scientific minds.

NPR's David Kestenbaum reports.

DAVID KESTENBAUM reporting:

It's sometimes said that while democracy works, you don't want to see how the sausage is made. It was the same today in Prague, where the International Astronomical Union held its vote in a large auditorium. The wheels of democracy were grinding very slowly.

Ms. JOCELYN BELL BURNELL (Neutron Star Specialist): I think this microphone is working okay.

KESTENBAUM: Jocelyn Bell Burnell, normally a specialist in neutron stars, today her job - get everyone to vote on the definition.

Ms. BURNELL: You may have been given a white sheet with a resolution in English on it. That white sheet is wrong.

KESTENBAUM: The definition had been changed many times since the meeting began. Last week an official panel recommended keeping Pluto as a planet and adding at least three, perhaps 40 more small objects. But that proposal, which had been drafted in secret, led to an uproar and many, many revisions. Today Astronomer Richard Binzel stood at the podium and read the final proposal so it could be voted on.

Mr. RICHARD BINZEL (Astronomer): The word planet is strictly defined to be a body rounded by self-gravity, which has cleared its orbital zone.

KESTENBAUM: Tiny Pluto would not count. It doesn't have the mass to kick its neighbors out. The suburbs of the solar system are filled with small, icy objects, including Pluto. But astronomers continued to debate. Question, what about planets outside our solar system? Answer, this definition is just for our solar system. Question, and what about Neptune? It's not fully alone in it's orbit.

Unidentified Man: Is Neptune a planet, because everybody knows that Neptune's orbit is crossed by Pluto's.

KESTENBAUM: Answer?

Mr. BINZEL: Footnote One.

KESTENBAUM: The resolution had a footnote explicitly naming the eight planets. Well, someone said, why not drop the complicated definition and just leave the footnote? Everybody laughed. Then Michael Rowan-Robinson stood up to try to move things along. He's an astronomer and serves as the official representative of the United Kingdom.

Mr. MICHAEL ROWAN-ROBINSON (Astronomer): It would be disastrous for astronomy if we come away from the general assembly with nothing. We will be regarded as complete idiots.

KESTENBAUM: Time for the vote. President Ron Ekers, white-bearded and serious.

Mr. RON EKERS (International Astronomers Union): So will those members in favor hold up the yellow card?

KESTENBAUM: An enormous number did.

Mr. EKERS: Then I believe the resolution is clearly carried.

(Soundbite of applause)

KESTENBAUM: And Pluto was out. The resolution does make Pluto one of a number of dwarf planets, which confusingly are not officially planets. So there are eight planets in the solar system, not nine and not 10. Until today, Mike Brown at Cal Tech could claim credit for finding what was arguably the tenth planet. It's been dubbed Xena, and it's bigger than Pluto. It, too, is out.

KESTENBAUM: So Mr. dwarf planet discoverer.

Mr. MIKE BROWN (California Institute of Technology): The largest dwarf planet, please.

KESTENBAUM: Brown says he's actually happy about the decision today.

Mr. BROWN: This is great. This is the definition that we should have had all along. When people think of the word planet, they think of large, special objects, and when you tell people about Pluto and make them realize that Pluto really is quite small, people even start to realize well, okay, maybe Pluto shouldn't be called a planet.

KESTENBAUM: Part of him, though, is a little sad.

David Kestenbaum, NPR News. Transcript provided by NPR, Copyright NPR.

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David Kestenbaum is a correspondent for NPR, covering science, energy issues and, most recently, the global economy for NPR's multimedia project Planet Money. David has been a science correspondent for NPR since 1999. He came to journalism the usual way — by getting a Ph.D. in physics first.