Planet

A planet is a large celestial body usually but not necessarily orbiting a star and not orbiting another planet, thus distinguishing planets from moons.

There are two primary classifications of planets. The first and most familiar to us is solid rocky bodies such as Earth and Mars. The other category of planets is gas giants such as Jupiter and Saturn.

There is no formal definition for what consitutes a planet at this time. The recent declassification of Pluto as a planet has shown the need for one and also how the lines can be fuzzy between a planet and smaller celestial bodies. Planets have been discovered orbiting stars other than our own. Some are far larger than Jupiter and thus seem to blurr the line between planets and brown dwarf stars, thus further complicating the process of producing an official definition.