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MELISSA BLOCK, host:

How do you solve the problem of Pluto? That's the question before the International Astronomical Union, which began its conference in Prague today.

MICHELE NORRIS, host:

The astronomers will vote next week on whether Pluto should retain its status as a planet, the ninth planet in our solar system.

BLOCK: Kelly Beatty is executive editor of Sky & Telescope Magazine. And Kelly, why this big dispute over Pluto? What's the big question here?

Mr. KELLY BEATTY (Sky & Telescope Magazine): Pluto is the misfit, the underdog, of the solar system. It's the one that's far out there and it doesn't really fit all the other planets. It's really small. And because of that its status as a planet has been in doubt for some time.

BLOCK: Is it really just a question of size?

Mr. BEATTY: Well, there's more to it than that. It's smaller than the moon, for example. It's only about 1,400 miles across, it's got an oddball orbit and most importantly, there are a bunch of other large objects out beyond Neptune - sometimes called the Kuiper Belt - that are comparable in size to Pluto. And one was discovered last year, and that's brought the whole thing to a boil.

On the other hand, there are some valid arguments for Pluto to be a planet. For example, it's been called that for 75 years and there's something to be said for tradition. Also, it's got an atmosphere, it goes through seasons and it's got three moons.

BLOCK: And it does have its fans.

Mr. BEATTY: Well, it does. School children the world over have learned that my very educated mother just served us nine pizzas is a great way to remember the nine planets as we've known them.

BLOCK: You know I was going to say - but I learned just served us new pickles.

Mr. BEATTY: Oh, ok.

BLOCK: Would there be people in the astronomical world who would say Pluto is just an unfortunate mistake?

Mr. BEATTY: Indeed there are. Most astronomers, I think, if you took a poll right now, certainly those who study the solar system would argue against Pluto having major planet status. And, you know, it's not completely unprecedented. The four largest asteroids, when they were discovered hundreds of years ago, were known as planets initially, but then we discovered that they were part of a whole belt of asteroids and they were demoted.

I think times are a little bit different. There is so much inertia, so much more communication now, that the astronomers if they vote in favor of demoting Pluto will have a lot of that to contend with. I mean, Pluto is such a part of our understanding and our education of what the solar system is all about. It would be difficult to wrest that notion from people's heads.

BLOCK: Well, tell us about the discovery of Pluto in the first place.

Mr. BEATTY: Back in 1930, a young farm boy from Kansas named Clyde Tombaugh had been hired by Lowell Observatory actually to try to find the ninth planet based on some predictions made by Percival Lowell, the observatory's founder. And in very short order, just a few months, he discovered this object approximately in the right place.

And the astronomers at Lowell observatory didn't come up with the name Pluto themselves. That fell to an 11-year-old Oxford schoolgirl named Venetia Burney, who was very well versed in mythology and said well, it makes sense that we should call it Pluto because Pluto is the god of the underworld and this is the most distant, dim object.

Well, Ventia's grandfather knew an astronomer who sent a telegram to Lowell Observatory and voila, she gets credit.

BLOCK: Well, if Pluto is declassified, what does it become?

Mr. BEATTY: There's been some talk of creating a third class of planets. The major gas planets, which are Jupiter, Saturn, Uranus and Neptune. The rocky, terrestrial planets: Mercury, Venus, Earth and Mars. And then a third class called dwarf planets, which Pluto and perhaps a few other members out there in the Kuiper Belt might be members of.

We'll just have to wait until Wednesday of this week when they announce their recommendation.

BLOCK: And all those maps of the solar system will have to be redone in some way? I mean, how do you - sounds like you would have sort of a Stalinist purge of Pluto here.

Mr. BEATTY: It would be a very dramatic turning point in the history of astronomy, for sure.

BLOCK: And we'll need a whole new mnemonic.

Mr. BEATTY: That's right. A different kind of pizza or pickle.

BLOCK: Kelly Beatty, thanks for very much.

Mr. BEATTY: My pleasure, Melissa. Thank you.

BLOCK: Kelly Beatty is executive editor of Sky & Telescope Magazine.

You can find out more about Percival Lowell and how his Mars mania led to the discovery of Pluto at NPR.org.

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