It's official: Pluto isn't a planet any more. The IAU has spoken.
There's been a lot of bellyaching about this. A mysteriously large number of people (people with Web logs, anyway) apparently have a sentimental attachment to a large ball of ice three billion miles away. They're sad that it's been voted off the island, so to speak.
Well, I'm not. I'm glad the IAU has decided to uphold some standards, and I'm not ashamed to admit it. Pluto was always a lousy excuse for a planet. It's ridiculously small: not only is it smaller in diameter than the Earth's Moon, it's only a sixth of the Moon's mass. That's not a planet. And, just to rub it in, astronomers have discovered several Kuiper Belt objects which are actually bigger than Pluto.
So the IAU had the choice: kick a ridiculously substandard planet out of the club or open it to literally dozens of other obscure balls of ice with names like "Xena" or "Quaoar." They chose the path of sanity. Planets -- real planets -- are substantial bodies orbiting the Sun in regular orbits. Pluto is now just one of a whole passel of trans-Neptunian icy objects. Good riddance.
If Pluto wants to be accepted as a real planet, it can come back when it's gained about 50,000,000,000,000 megatons of mass. Maybe put on some rock or iron. Work up some surface gravity. Then we'll talk.