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The Pluto Exception


In August, the IAU decided on a definition of a planet. Please read Akkana’s article on page 4. The new definition removed Pluto from the list of planets. Many of my favorite astronomers, people like Alexei Filippenko and Neil deGrasse Tyson, are probably happy with that result. I have to agree that the new definition was better than the committee-created resolution which would have resulted in a planetary delta of +3 instead of -1. And I’m also glad that we now have a “scientific” definition of the word planet. But I want to argue for one small modification: the Pluto Exception.

I probably don’t have to explain what I mean — make an exception for Pluto. Let the astronomers have their new definition of a planet but keep Pluto in the list of planets in this solar system. Feel free to use the new definition to keep Ceres, Charon and Xena from becoming planets but leave Pluto as is.

Would this violate some deep scientific principle? If so, astronomy has plenty of precedent. Betelgeuse is listed as Alpha Orionis even though Rigel is the brightest star in Orion. M40, in the Messier list of “fuzzies” that could be comets, is actually just a double star but we don’t remove it from the list (and there was no trouble in removing M102).

And there are still other things that make Pluto unique even today. Some of these are scientific and some are cultural. The scientific unique attributes are: discovered 70 years before another object of the same size was discovered, 3 moons, and a barycenter that is not within Pluto. The cultural attributes include: named by an 11-year old girl, coincidentally named the same as the popular Disney character in the same year, and part of numerous mnemonic devices such as My Very Educated Mother Just Served Us Nine Pizzas.

So I think we have reason and precedent for declaring Pluto an exception, an exceptional planet. And I think if the powers-that-be in this debate didn’t have to worry about Pluto’s inclusion/exclusion, we would get a clear definition that would not requires years of debate. For grins see/listen



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