August 25, 2006
Well, apparently I spoke too soon. Twelve planets must be too many; instead the IAU opted to demote Pluto instead. So we're down to the eight we started the 20th century with and Clyde Tombaugh has been relegated to the same status as... um... ol' whatshisname who discovered Ceres.
The logic is a bit weird... apparently Pluto got demoted to "drawf planet" because it hasn't "cleared out" its orbital space. If you have no idea what that means you're not alone. Is it because the Pluto-Charon CoM is outside the body of Pluto? Hell, that means the Earth will cease to be a planet in a couple billion years.
Or is it because its orbit crosses Neptune's? (It really doesn't; the crossover only looks that way from a certain angle, and the two planets are never there at the same time regardless.) Wouldn't that make Neptune stop being a planet?
If they really want to get rid of Pluto, it's easy: Say a planet must be at least 4000 km in diameter -- Mercury's in by a comfortable margin and Pluto and "Xena" are too small.
So, eight planets. Not nine, not twelve. But it'll probably stay nine for quite a while, regardless of what the propellerheads say.
