Dwarf planet

A body that orbits the Sun, is nearly round under its own gravity, and has not cleared its orbital neighborhood. It is not a satellite.

International Astronomical Union: An international organization of professional astronomers that standardizes astronomical nomenclature and definitions. Its 2006 resolution established the formal definition of a dwarf planet.
Pluto: A dwarf planet in the Kuiper belt, discovered in 1930 and reclassified from planet in 2006. Its reclassification made the new dwarf-planet category widely known.
Pluto's planetary status: The historical classification of Pluto as a planet before its 2006 reclassification. The dispute over Pluto prompted astronomers to formalize a separate category.
List of possible dwarf planets: A collection of Solar System bodies proposed as dwarf planets but not formally recognized as such by the IAU. Many likely round bodies remain unclassified because their sizes and shapes are uncertain.
Hydrostatic equilibrium: A state in which gravity and pressure balance, giving a fluid or sufficiently deformable body a rounded shape. This physical condition underlies the definition's requirement that a body be nearly round.
Ceres: A dwarf planet in the asteroid belt and the largest object in that region. It is the only recognized dwarf planet inside Neptune's orbit.
2006 IAU definition of planet: The International Astronomical Union resolution defining planets and dwarf planets in the Solar System. This resolution named dwarf planets as distinct from the eight planets.
Planetary discrimination: A proposed quantitative measure of how effectively an orbiting body dominates its orbital region. It offers a numerical interpretation of the IAU's orbital-clearing criterion.
Orbital neighborhood: The region around an orbit in which a body can gravitationally dominate or remove competing objects. Clearing this region is the defining condition that dwarf planets fail to meet.
Eris: A distant dwarf planet discovered in the scattered disk beyond Neptune. Its discovery intensified debate over Pluto's planetary status.

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