[Update: Pluto’s not a pluton. More here.]
So Pluto’s still a planet, but they’ve now classed it and a few other planet-like things as a separate class of planets called “Plutons.” That’s right, in the process of defining “planet” for the first time in history, we’ve been forced to include even more planets in our system. So now, if this new definition gets passed, we’ll have 12 planets in our solar system (though Pluto and Charon are now called a “double planet” for reasons that I don’t quite understand yet). Now we need a new mnemonic to remember Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto-Charon, and UB313. First we need a better name for “UB313,” if you ask me, though nobody has yet. Talk about a name that’ll get you teased in middle school!
Oh, and the “definition” that they (the IAU) drafted only requires that the mass in question orbit a star and be spherical, which could include a whole bunch of masses. But borderline cases have to be observed and approved (by vote?) before they can be defined as planet.
So, what’ll it be. What’s the mnemonic that’ll make it into grade school text books for the next few decades?