Scientific American is reporting that, after much debate, Pluto has been stripped of planet status by the International Astronomical Union. To which I say, duh. Pluto’s a dog.
The official definition of a planet is now:
A planet is 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.