Extrasolar planet definition

Comparison of Eris, Pluto, Makemak

In 2003, The International Astronomical Union (IAU) Working Group on Extrasolar Planets made a position statement on the definition of a planet that incorporated the following working definition, mostly focused upon the boundary between planets and brown dwarves:^[2]

1. Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 times the mass of Jupiter for objects with the same isotopic abundance as the Sun^[40]) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass and size required for an extrasolar object to be considered a planet should be the same as that used in the Solar System.
2. Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed or where they are located.
3. Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

This definition has since been widely used by astronomers when publishing discoveries of exoplanets in academic journals.^[41] Although temporary, it remains an effective working definition until a more permanent one is formally adopted. However, it does not address the dispute over the lower mass limit,^[42] and so it steered clear of the controversy regarding objects within the Solar System. This definition also makes no comment on the status of planets orbiting brown dwarfs such as 2M1207b. A sub-brown dwarf is a planet-mass object that formed through cloud-collapse rather than accretion. The distinction between a sub-brown dwarf and a planet is unclear; astronomers are divided into two camps as whether to consider the formation process of a planet as part of its division in classification.^[43][44]

e, Haumea, Sedna, Orcus, 2007 OR₁₀, Quaoar, and Earth (all to scale).