Were you, like me, bummed when back in 2006 when the International Astronomical Union decided that Pluto wasn't a planet? Well, fear not! We may be getting our favorite tiny celestial entity back as one of the official "planets". Maybe.
Originally, Pluto was booted because there appeared to be a bunch of other big rocks just like Pluto in the same general vicinity, and they're all considered too small to be called a planet.