Dwarf Planets May Finally Get Respect
An international panel has unanimously recommended that Pluto retain its title as a planet, and it may be joined by other undersized objects that revolve around the sun.
Some astronomers had lobbied for reclassifying Pluto because it is so tiny. And at least one major museum has excluded Pluto from its planetary display. But sources tell NPR that under a proposal to be presented at a big meeting of astronomers in Prague next week for a vote, Pluto would become part of a new class of small planets. Several more objects could be granted membership.
When Pluto was first discovered in 1930, its planethood was not in question. Early estimates put it at perhaps five times the size of the Earth. Over the years, measurements have consistently shrunk.
Does a Planet's Size Matter?
Pluto is now thought to be smaller than Earth's moon. It has a cockeyed orbit. And most damningly, astronomers now know it is just one of hundreds of rocky things at the edge of the solar system called Kuiper Belt objects. Pluto is larger than most, but one recently discovered Kuiper Belt object -- UB313 -- seems to be larger than Pluto.
So earlier this year, the International Astronomical Union, which has decided tricky nomenclature issues since it was formed in 1919, appointed a panel to try to define the word "planet."
Seven experts, including a science writer and a variety of astronomers, met in Paris this past June. Under the guidance of Owen Gingerich, a historian and astronomer emeritus at Harvard, they debated for two days.
Gingerich would not discuss the conclusions, but says "I think we have done something that will make the Plutocrats and the children of the United States happy."
NPR interviewed five of the seven panel members. All but one said they thought of Pluto as a planet, or had made statements in the public record to that effect.
Dava Sobel, the writer on the panel, was sympathetic to Pluto's cause. In her book The Planets, Pluto merits a chapter.
"People love Pluto, children identify with its smallness," she writes. "Adults relate to its inadequacy, its marginal existence as a misfit." Sobel has several solar system models in her house. Asked if she had torn Pluto off any of them, she said "No, Pluto is definitely there."
New Category: Dwarf Planets
Several panel members have favored dividing planets into categories: terrestrial planets (Mercury, Venus, Earth, Mars), giant planets (Jupiter, Saturn, Uranus, Neptune) and a third class that would include Pluto.
"We'll call them dwarf planets or something," says Iwan Williams, an astronomer at the University of London who favors the idea and also served on the panel.
Sources say the panel's new definition for planets would, in fact, create a third category embracing Pluto.
It's unclear what astronomers will make of the new definition or how they will vote on it. Observers say the definition will have to be concise and unambiguous. What is too small to be a dwarf planet? Do moons count? What about round comets?
Some panel members say they favor counting any object which is large enough that its gravity has made it round. If the object is spinning, a small bulge would be tolerated. "We're talking about no more than four or five new planets," says Iwan Williams.
Small potato-shaped asteroids wouldn't make the cut. But Ceres, a big round asteroid between Mars and Jupiter, might qualify.
The panel's recommendation is being reviewed by the International Astronomical Union's executive committee. In an interview last week, executive committee member Bob Williams said the definition proposed by the panel had some potential problems, and he was not at all sure if the astronomers voting in Prague this month would approve it.
"At this point, I don't feel confident enough to bet in favor of it," he said.
It may be that the objects of the solar system are too varied to be put into neat human categories. Williams is hopeful though.
And he hopes the final definition will fit on two pages.
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RENEE MONTAGNE, host:
An international advisory panel has reached a verdict on whether tiny Pluto should retain its grand title of planet. Astronomers have been debating what a planet is and whether Pluto counts. At least one museum has barred Pluto from its display of the planets. A formal resolution based on the panel's decision will be voted on later this month in Prague. It's been treated as top-secret.
NPR's David Kestenbaum has this cosmic scoop.
DAVID KESTENBAUM reporting:
Pluto was discovered in 1930 by a young astronomer named Clyde Tombaugh working at an observatory in Arizona. At the time, there were very good reasons for calling it a planet. Iwan Williams is an astronomer at the University of London.
Mr. IWAN WILLIAMS (Astronomer, University of London): Back in the '30s, it was thought to be much bigger than the Earth and figures like five times the size of the earth was bandied about. And then, as our knowledge of Pluto grew, we realized it was sort of smaller and smaller in real size until now we know it is much smaller than the moon.
KESTENBAUM: There are other problems. Pluto has a cockeyed orbit, and astronomers now know it is just one of a swarm of objects at the edge of our solar system called Kuiper Belt objects. One of them, currently named UB313, is thought to be larger than Pluto.
So are all these things planets? Some of them? None of them? If a planet is something that sits alone in its orbit, then they're all out. But a different definition could expand membership to perhaps 60 planets.
So this year, the International Astronomical Union appointed an elite multi-national seven-member panel to try to come up with a simple definition for planetness. They operated under the guidance of one brave man.
Professor OWEN GINGERICH (Harvard Smithsonian Center for Astrophysics): This is Owen Gingerich, professor of astronomy and of history of science emeritus at the Harvard Smithsonian Center for Astrophysics.
KESTENBAUM: As soon as Gingerich as picked, people came by his office to lobby him.
Prof. GINGERICH: People saying, but little children love Pluto. They'll be brokenhearted if you take it away.
KESTENBAUM: The cruel, mean people also came by, arguing Pluto should be demoted. The thing is, they made a strong argument.
Prof. GINGERICH: People came and said that was a scientific mistake made in 1930. We've come a long way. We know so much more about what's in our solar system. We shouldn't perpetuate this scientific mistake.
KESTENBAUM: The panel met for two days in Paris this summer. No blood was spilled. No pencils were snapped in half. Miraculously, the members came up with a definition that they all agreed on. It was new, ingenious, and very hush-hush.
Can you tell me what it is you recommended?
Prof. GINGERICH: I would be nailed to the wall by my colleagues if this produced a leak, so I can't tell you.
KESTENBAUM: Mm hmm. Well, some of the members are already on record with their opinions. Like the author Dava Sobel, who recently wrote a book called The Planets. You can see where her sympathies lie in the chapter on Pluto.
Ms. DAVA SOBEL (Author, The Planets): People love Pluto. Children identify with its smallness. Adults relate to its inadequacy, it's marginal existence as a misfit.
KESTENBAUM: Do you have any - do you have a model of the solar system at home or anything like that?
Ms. SOBEL: I have several.
KESTENBAUM: And do those models of the solar system include Pluto, or have you torn it off?
(Soundbite of laughter)
Ms. SOBEL: No, Pluto is definitely there.
KESTENBAUM: NPR interviewed five of the seven panel members, and all but one have said they think of Pluto as a planet of some sort. And sources tell NPR the panel did recommend a definition that would include Pluto. No one would reveal the details, but several panel members favor the same approach: set up different categories of planets.
Iwan Williams served on the panel. His scheme would have rocky inner planets: Mercury, Venus, Earth and Mars - the giant planets: Jupiter, Saturn, Uranus and Neptune - and a third category of smaller things that would include Pluto.
Mr. WILLIAMS: And we say, okay, there's now a new group of planets which we'll call - for the sake of argument - dwarf planets or something, as opposed to the giant planets being very big and the dwarf planets being fairly small.
KESTENBAUM: That's a nice idea, but scientists aren't going to vote for it without a clear definition of what falls in what category. When is an object too small to be a dwarf planet? Are moons planets? What about big, round comets? The pornography definition - I'll know it when I see it - just doesn't work.
Williams personally favors counting any object which is large enough that gravity has made it round. If it's spinning, you could allow a little bulge.
Mr. WILLIAMS: You're probably talking about no more than four or five new planets.
KESTENBAUM: This would rule out small potato-shaped asteroids. Ceres - a big round asteroid between Mars and Jupiter - might qualify. But the astronomers who will vote this month may have their own ideas. The panel's recommendation is being reviewed by the International Astronomical Union's executive committee.
Bob Williams is on that committee. He thinks there are still some problems with the definition. He's not at all sure what will happen at the vote in Prague. I met him at a bar in Baltimore to try to pry loose some information.
Mr. BOB WILLIAMS (Executive Committee Member, International Astronomical Union): I think that a consensus may well be problematical. I wouldn't put money on it at this moment. And you're talking to the guy who basically is framing, right now, trying to frame the resolution.
KESTENBAUM: Can you tell me what the recommendation of the panel is?
Mr. WILLIAMS: No, I can't, unfortunately. I can't.
KESTENBAUM: What if I buy you another beer?
(Soundbite of laughter)
Mr. WILLIAMS: Good try.
KESTENBAUM: Williams hopes to have a final, ultimate, definitive definition of a planet ready soon. He wants to keep it shorter than two pages.
David Kestenbaum, NPR News. Transcript provided by NPR, Copyright National Public Radio.
