This has been bothering me for some time, no one has a good answer to it. I read a while ago some information about the meaning of "planet" and it said that Pluto isn't a planet, that there are just 8 planets in our solar system. Why? I read that the meaning of "planet" is: A solitary body, for example the Earth, there are no other bodies close ti it with the same characteristics (size especially) so it is a solitary body. Ceres used to be considered a planet long ago but when people found out that there were other asteroids about the same size as Ceres and close to it they re-clasified Ceres as an asteroid (The Asteroid Belt between Mars and Jupiter). Same with Pluto, there are bodies about the same size of Pluto near him (the Kupier Belt) so according to the meaning I read Pluto wasn't a planet. Same with Sedna, they don't want to consider it a planet because if someone in a near future finds that it belongs to a population of similar bodies then they will have to re-clasify Sedna. Can anyone explain this to me? English is my second language and it's hard for me to explain myself in English so if you don't get my point, please let me know so I can post the site in which I found the information.