On August 24, the International Astronomical Union is going to vote on a proposal (here is the official resolution) to define the term “planet” such that Pluto stays in, and three bodies get added. This would require the re-writing of textbooks and make millions of first-graders learn 12 planets instead of nine. The planet status of Pluto has long provoked heated and fairly pointless and silly debate, much of it by people who are only vaguely familiar with astronomy but feel strongly about the definition of planet, a tradition which I fully intend to continue here.
At first I thought that the IAU proposal was to include Pluto, Xena (UB313), Sedna, and Quaoar as planets, perhaps getting the “ice dwarf” category. This was obviously the right thing to do, since rewriting textbooks is a good thing, and I think 21st-century first graders can handle it, and those various ice dwarves were probably tossed out of the inner solar system by other planets during the formation of the early solar system and so probably formed in a similar fashion originally. This also made for a nice symmetrical classification: 4 inner rocky planets, 4 outer gas giants, and 4 ice dwarf planets even further out. Everyone can remember that, even after we add more ice dwarf planets as we are likely to do.
But then I learned that the candidates for official planethood were not the above, but instead Pluto, Pluto’s moon Charon, Sedna, and the asteroid Ceres. Pluto and Sedna I can deal with, but Charon clearly belongs with the other two moons of Pluto. Pluto is 9 times more massive than Charon, we can’t let it schlepp itself up to planet status just because it happens to be just big enough to move the barycenter outside the surface of Pluto. If we go down this route, soon people will be calling the Earth-Moon system a double-planet – the earth-moon barycenter is a mere 1700 km below earth’s surface, after all.
And Ceres – I should say up front I’ve got nothing against Ceres, she’s a spunky little planetoid. And clearly we need to send a probe to get some decent pictures as soon as possible, because the Hubble shots are frustratingly fuzzy. And sure, she’s vaguely spherical. But c’mon, let’s get real. She’s less than 1000 km across. Heck, the great state of California is by itself 1,240 km long. If you get up early and take I-5 you can drive the whole thing by 9 pm. I know some people think California seems like it is its own planet already, but if we let Ceres in, we’ll have to let in Vesta, Pallas, and Hygiea, and while this would make another nice group of four, 16 is way too many for the first graders to learn. And Hygiea is only 300 x 500 km. I mean, Oregon is 420 x 580 km, and if we start calling Hygiea a planet pretty soon Oregon will want to be treated like California, or at least a moon of California. Clearly, it’s a slippery slope, and that way lies chaos.
It looks like I’m taking on consensus of the astronomers over 2 years of debates, so maybe I’m off my rocker. Are they right? Have at it in the comments.
(Note: any similarities between this post and a Stephen Colbert report are purely accidental.)