You have to feel for Pluto. If you’re like most of us earthlings, you probably learned as a kid that there were nine planets in the solar system, and Pluto was the most distant of them.
Not any more, if a committee of the International Astronomical Union has its way. For years there’s been a movement among astronomers to demote Pluto from planethood–it was too puny, too different from the others.
No longer. Instead of removing Pluto from the list, they’ve recommended that the definition of "planet" be expanded to include any body that orbits the Sun and is large enough to be sprerical–and Pluto isn’t even the most far-out. That distinction belongs to 2003 UB313, discovered last year. Ceres, the largest of the asteroids between Mars and Jupiter, was briefly a planet in the early 1800s; now it’s back. Even Charon, Pluto’s largest moon, is large enough to make the newly-proposed list.
There will be some more interplanetery warfare over this. The full IAU has to approve at its current meeting in Prague. But start to re-teach your kids: twelve planets…twelve planets.
There’s a bit more HERE.