Why Did Pluto Get the Boot? Pluto is no longer one of the nine planets of the solar system. Instead, astronomers say it should officially be considered a dwarf planet, while the solar system should encompass the eight classical planets. We'll look at the scientific thinking behind the decision.
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Why Did Pluto Get the Boot?

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Why Did Pluto Get the Boot?

Why Did Pluto Get the Boot?

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A program note: A year ago, Hurricane Katrina howled ashore, and the residents of the Gulf Coast fled homes and neighborhoods. Some have never been seen again. Now for next week's SCIENCE FRIDAY, we want to know where you are. So for TALK OF THE NATION on Monday, we want to know where you are, where you've shown up. If you left the Gulf Coast because of Katrina, we want you to e-mail your story to TALK OF THE NATION. On Monday we'll be talking about it on that show with Neal and his guests. Here's your e-mail address: talk@npr.org, that simple: talk@npr.org. That's for Monday's TALK OF THE NATION from NPR News.

We're going to continue now and talk about something that happened this weekend, something strange to a lot of people, what happened to Pluto. Pluto is gone. It's no longer a planet. That's the latest decision by the folks who decide what a planet is. That's the International Astronomical Union. And after a roller coaster of debate, yesterday its members voted to drop Pluto from the ranks of planetdom, keep the number of classic planets to eight.

Joining us now to talk more about why museum gift shops must now re-label their inventory is NPR's science correspondent David Kestenbaum. David, welcome to Science Friday.


Hi, Ira.

FLATOW: It sounded like there was a raucous debate going on there.

KESTENBAUM: Yeah. What's next, Rhode Island?

(Soundbite of laughter)

KESTENBAUM: It was a total, stunning reversal of fortune. Because this had been something that had been debated for years, and in June the International Astronomical Union appointed a secret little group to gather in Paris and try and come up with something they thought everyone could agree on. And they thought they'd done it, and they were very excited about it. And it got presented at the meeting, and it was totally torn to shreds.

And their proposal would've kept Pluto. It was what you might call a structuralist approach, and they basically said look, a planet is, you know, it's round. It's big enough that gravity has pulled it into a round shape. And when you think about that, it makes a lot of sense. But then when you write down your definition, you realize, oh, we're going to have include Pluto's moon, Charon, oh, and there's this asteroid in the asteroid belt called Ceres that counts also, and oh, maybe there are a dozen, two dozen, three dozen, maybe four, five dozen other things out by Pluto which are going to count also, and I think that, you know, there are people to whom that didn't seem quite right, either.

FLATOW: So what did they decide to do with Pluto?

KESTENBAUM: Well, so there was an alternate proposal that was put forward which added one requirement. It said it has to be round, it's got to go around the sun, but it also has to be a gravitational bully. It has to be big enough that it can clear out any riff-raff from, you know, from the area, from its orbit. And Pluto doesn't count because it's part of the Kuiper Belt, and there are hundreds of objects out there.

So that passed overwhelmingly. People stood in this big auditorium, they held up a yellow card, and they didn't even count the no votes because it was clear.

FLATOW: We're talking with David Kestenbaum, NPR's science correspondent, on TALK OF THE NATION: SCIENCE FRIDAY from NPR News. So now they have this added -so now we'll have describe basically in different wordage what these different objects are: Pluto, the planets, and these other objects?

KESTENBAUM: Pluto is counted as a dwarf planet, but they say it's not a planet. They actually - there was an amendment offered where they were putting, they put it in quotes.

(Soundbite of laughter)

KESTENBAUM: It's important that it be, quote, dwarf planet, end quote, and there are going to be probably a bunch of those, and then there are other small things in the solar system. But they did vote to give Pluto some special kind of designation, but they couldn't come up with a name.

FLATOW: They were going to say Plutino(ph) or something, right?

KESTENBAUM: Plutino, Pluntonian. Plutonian was close, but I think it was 186 to 183. And so yeah, Pluto's special, but we don't quite know what we're calling it yet, and some future subcommittee of a committee of a committee is going to decide that.

FLATOW: You know, do the astronomers really care about this? I mean, you know, they know what it is, it's just the nomenclature they're stuck on.

KESTENBAUM: Right. So there's a whole category of people who say I don't care what it's called. It is what it is. Clyde Tombaugh, who discovered it - his wife - he died - but his wife said apparently before he died he said well, it is what it is. You know, it's a big rock out there that people are interested in as a big member of the Kuiper Belt.

So there are people in that category, but, you know, there are definitely Pluto-huggers out there and people who, for historical reasons, want to keep it. And there are other people who said look, it's ridiculous to include this teeny-tiny little rock, you know, along with the other big things.

FLATOW: And you had already some planetariums that had take it out of its - out of their other exhibit area.

KESTENBAUM: The Rose Center, the planetarium in New York - if you talk to Neil deGrasse Tyson, who runs it; he says look, we didn't take it out, we never had it.

(Soundbite of laughter)

KESTENBAUM: But where they actually put it is in the Kuiper Belt exhibit and they do call the other things planets, so you can see why he's got a file of hate mail from kids, which he does have.

FLATOW: Right. And headaches in a museum shop where they probably have objects that still say Pluto.

KESTENBAUM: I think this is going to increase support for Pluto. You know, I think people are really going rally behind this little thing. But he did - Neil said that if the vote had gone the other way, if Pluto had been included, he was going to go down and he would've etched in a new inscription to say, by the way, this is considered some sort of planet or something. But he was among the people who really didn't care. He thought it was the least interesting question you could ask.

FLATOW: Well, you know, but it stirred up debate. People are talking about the planets and the solar system like they never have.

KESTENBAUM: It's true. I mean it's a much more interesting thing to talk about, like, how would you define a planet. It turns out it's really hard. Because you say it's big and round, well then what about our moon?

FLATOW: Right.

KESTENBAUM: You know, that's plenty big and round. Or Europa. It just becomes very hard. You do start to think it's like saying what's the difference between a river and a stream. You know, the Supreme Court held - once there was some case in which the Supreme Court...

FLATOW: We won't go there today, but you're right.

KESTENBAUM: So, you know, it's hard to...

FLATOW: All right. We've run out of time. David, thank you very much for taking time to talk with us about Pluto.

KESTENBAUM: You're welcome.

FLATOW: David Kestenbaum is a science correspondent for NPR.

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