Ira Flatow on Science: Is Pluto a Planet?

Astronomers recently discovered two more moons orbiting Pluto in addition to its already-discovered moon, Charon. Madeleine Brand talks with Ira Flatow, host of NPR's Talk of the Nation Science Friday, about the discovery and how it's fueled renewed controversy over Pluto's status as a planet.

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MADELEINE BRAND, host:

This is DAY TO DAY. I'm Madeleine Brand.

For decades, Pluto was a planet--a little on the small side, maybe, but still a planet. Then in recent years, some astronomers said it wasn't a planet. And now this week, complicating the whole debate comes news that Pluto may actually have three moons orbiting around it. So what does that mean for Pluto's planet status? Here to shed some light--some moonlight, perhaps--is Ira Flatow, host of "Science Friday" and a regular Thursday contributor to DAY TO DAY.

Hi, Ira.

IRA FLATOW (Host, "Talk of the Nation/Science Friday"): Hi there.

BRAND: So does this mean Pluto is a planet?

FLATOW: That is such a great cocktail party question, because it depends on what you mean by the definition of a planet, and it's getting hazier and fuzzier all these decades now, because Pluto actually lives and behaves more like what they call a Kuiper Belt object. Now outside of the planet Neptune, which we know is a planet, there's like a junk graveyard of the remnants of the leftover debris of when our solar system was made, let's say, four billion years ago--a lot of rocky little stones, ice-covered stuff, which Pluto is more like than it is, you know, Uranus, Neptune, the Earth. And so astronomers now are saying, you know, maybe Pluto is really a Kuiper Belt object. It has a weird orbit; it's more inclined and eccentric, as they say, behaving just like these Kuiper Belt objects. And in fact, some of them are called Plutinos because they're almost of the same shape as Pluto.

But now comes the fly in the ointment, so to speak. Here comes the news that Pluto has three moons circling it, not just one moon, the Charon that we knew about, but two more moons. And in a sense, the astronomers are saying, `Well, does it make it now more like a planet, or should we still call it more like, you know, a Plutino sort of thing?' And...

BRAND: So will we ever know? How do we find out?

FLATOW: Well, we'll just have to decide on what the definition of a planet is, you know, because on the other hand, there are tens of thousands of other Plutinos, Pluto-like objects out there, and they probably have moons circling them also, like Pluto does, but we just haven't discovered them. If we look hard enough at them out there in the Kuiper Belt, we may find them. So some astronomers have, you know, said, `Let's just keep things the way they are. We're very happy calling Pluto a planet.' And others, like the American Museum of Natural History, you know, the Hayden Planetarium there--they've actually removed Pluto from their exhibits. If you go out there to New York, which I have...

BRAND: Poor Pluto!

FLATOW: ...they have all the planets lined up, and you look for Pluto and it's gone. And...

BRAND: But to take its place, there was another recent discovery of a planet, right?

FLATOW: Well, yeah, there was another--the 10th planet, as they call it, another mysterious object that's even further out in the solar system. They haven't really looked very well at this one and, you know, it's not that easy to look at. So does that become the ninth planet, then? Does the 10th planet become the ninth planet and, you know, does the 10th planet remain the 10th planet? It's just sort of how you interpret and how you define what a planet is, and it's kind of interesting. But this debate will continue as we probably will find more Kuiper Belt objects that look like Pluto.

BRAND: Ira Flatow hosts "Science Friday" and a regular Thursday contributor to this program.

Thank you very much.

FLATOW: You're welcome.

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