When you went to bed last night, you knew that there were nine planets in our solar system. But when you woke up today, there were 12. That's right. Besides cementing Pluto's sometime-doubtful status as a planet, astronomers recently decided on a refined definition of planet that is large enough to include Ceres (a large asteroid), Charon (Pluto's moon) and a distant-orbitting object called Xena (like the warrior princess). Many other astronomers are up in arms.
