Pluto

The roller coaster news coming from the IAU conference in Prague was no doubt confusing for the casual follower of astronomical developments. Earlier in the week, the news was trumpeted that the solar system may soon number 12 planets, only to be followed by the final decision that trans-neptunian objects including Pluto were out. The planets now number eight.

One of the most fascinating angles of this whole debate is how upside down people can get about how to draw boxes around nature's fuzzy edges. After first hearing of the initial proposal, I was skeptical. However I came to feel that a scientific definition for a planet would be difficult to create if it ruled out planets beyond Neptune simply because it offended our sense of aesthetic. I thought we'd just have to get used to the idea of planets coming in hundreds instead of a handful. Besides, other star systems could very well turn our well manicured collection of four terrestrials, four gas giants, and a collection of hangers on into an oddity, once they were observed in more detail.

A "planet" is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

In the end the final resolution returns us to eight planets. I'm curious to see how easy it is to make the determination that a celestial body has cleared it's neighbourhood around its orbit. That seems like a very qualitative assessment to be making.

Again, the most fascinating aspect is the reaction of the general public. I find many reports in the popular press tend to give the impression that reality has somehow changed, rather than our description of reality. For instance, CNN's Pluto no longer a planet, say astronomers. It almost gives the impression that there was some kind of technical screw-up, rather than a rethink of a categorization system. I chalk it up to an educational system that puts more store in memorizing the names of nine planets, for regurgitation in an exam, polite company, or game show, than in understanding our reality as a complex entity that our classification systems attempt to simplify for convenience.