Pluto is a dwarf planet by the below definition and is recognized as the prototype of a new category. This category is being called "plutonian objects."

Aside from the 8 classical planets there are several non-planetary objects: Pluto, Charon, Ceres, and UB313 (a.k.a. Xena).

The IAU (Interational Astronomers Union) therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A classical planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".