A classical planet is any of the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, or Neptune. In 2006, astronomers agreed to distinguish between two types of planets: classical planets and dwarf planets. According to the new definitions, Pluto would be demoted to dwarf status.
A classical planet satisfies the following criteria:
1. It is in orbit around the Sun.
2. It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.
3. It has cleared the neighborhood around its orbit.
This definition was adopted by astronomers at a meeting of the International Astronomical Union (IAU) in Prague on August 24, 2006. It has, however, come in for some criticism on a number of grounds. For example, Neptune has not "cleared the neighborhood around its orbit," otherwise Pluto would not be where it is. The same can be said of Earth, Mars, and Jupiter, all of which have Trojans in similar orbits.