nonplanetary

Nonplanetary is a descriptive term used to denote any celestial body or object that is not a planet. It is not a formal taxonomic category and its exact meaning depends on context, but it generally distinguishes objects that do not meet the definitions used for planets. In discussions of the Solar System, nonplanetary encompasses a wide range of bodies, including dwarf planets, asteroids, comets, moons, meteoroids, and interplanetary dust.

The International Astronomical Union (IAU) provides the commonly cited framework for classifying planets: a planet must orbit a star, have sufficient mass to assume hydrostatic equilibrium (a rounded shape), and have cleared its orbital neighborhood of other debris. Bodies that meet the first two criteria but have not cleared their orbits are termed dwarf planets; all other objects that do not meet planetary criteria are typically grouped as nonplanetary or as small Solar System bodies. Consequently, nonplanetary covers dwarf planets, natural satellites, minor planets, comets, and many small particles.

In exoplanet research and broader astronomical contexts, nonplanetary can be used to describe objects that are not planets, such as brown dwarfs or stellar companions, depending on the criteria applied (mass, formation history, and orbital characteristics). Because the term is informal, its precise scope varies with scientific context and discussion.

Related concepts include planets, dwarf planets, small Solar System bodies, asteroids, comets, and natural satellites.