An Etymological Dictionary of Astronomy and Astrophysics

A new category of → astronomical objects in the → solar system introduced in a resolution by the 26th General Assembly of the → International Astronomical Union (IAU) on August 24, 2006. The characterizing properties are as follows:

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 not “cleared the neighbourhood” around its orbit; and
4. It is not a → satellite of a → planet, or other non-stellar body. The property 3 reclassified → Pluto from a planet to a dwarf planet because it has not cleared the neighborhood of its orbit (the → Kuiper Belt). The largest known dwarf planets are: → Eris, → Pluto,
   → Ceres, → Makemake, and → 2015 RR245.

See also: → dwarf; → planet.