Gingerich gave an overview of the discovery of new solar system bodies throughout the 18th and 19th centuries, and how for a while there astronomers had classified quite a few objects, which we now think of as asteroids, as planets. He spent a lot of the time on the subject in order to set up what had happened just prior to and at the IAU General Assembly in August. Gingerich had been named chair of the Planet Definition Committee, and they had come up with a rather good definition of the word "planet" that was based on science. Essentially, a planet would be a body whose hydrostatic equilibrium had resulted in a spherical shape. Objects below a certain mass can't achieve that shape because they don't have enough gravity. So in general, only objects of a certain mass would end up becoming spherical and therefore being designated as planets.
Those of us who followed the news know what happened next. Other astronomers started protesting about the 12-planet solar system, noting that the new definition would require admitting Charon, Ceres, and UB313 (now Eris) to the solar system as planets. Gingerich made a personal observation that some of this could have been discussed and hammered out better had not the press jumped on the controversy. I believe his exact words were, "The press loves a controversy."
Speaking of which, he also addressed the controversy over the attempt to designate Pluto-type bodies as plutons. He said that he had found the term pluton in an encyclopedia as a geology term, but he figured it wasn't used frequently enough to be a problem because it didn't show up in his Microsoft Word spellchecker.
He also made another important point that I wish I could quote verbatim, but I can't. I'll do my best to paraphrase it correctly. Essentially, he pointed out that much astronomical research is funded by the taxpayers, and that when the public feels strongly about an issue, it behooves the astronomical community to listen carefully before taking any drastic measures. He wasn't saying that the public should get to decide what is or isn't a planet, but that the public does need to be listened to. (Sad to say, it seems as if the members of the IAU who voted weren't in the mood to do so.)
The impression I got was that he would have been happy to have two different classes of planets, in order to keep Pluto a planet. Frankly, I think a lot of people feel similarly. If the IAU had created an overall classification called "planets," and had then created subcategories of "major planets" and "minor planets," I think most people would have been fine with Pluto being designated a minor planet. But they didn't do that.
After the talk, Nomi and I approached him to get our copy of God's Universe autographed, and we presented him with an SP3 mug in appreciation of his efforts on behalf of Pluto. He was delighted by the mug, and set it up on the lectern facing outward. My guess is that he wanted to show it to the second audience for the repeat of his talk. Nomi and I headed up to the observation area, where we had a chance to see Uranus through a Schmidt-Cassegrain reflector. And then, secure in the knowledge that there are folks at the CfA who still support Pluto, we wended our way home.
Copyright © Michael Burstein