isn't there used to be 9 planet and the last planet pluto does get excluded just because of some requirements that pluto doesn't meet? well i learned this in science class when i was in college. I don't know the exact reason why it got excluded.
Pluto was excluded from the list of planets, simply because it does not fit the formal definition of a planet. A planet of the Solar System is a celestial body that meets all of the following conditions:
1. orbiting the Sun ( not a satellite of another body);
2. having enough gravity to have a shape close to a ball;
3. near the orbit of which there is "space free from other bodies".