Planemo

Part of speech: noun

Pronunciation: /ˈplæ.nə.moʊ/

Definitions

1. A celestial object that is not classified as a full-fledged planet due to insufficient mass or gravitational dominance encompasses various small bodies that may drift through space independently of stars
2. This term describes a smaller astronomical entity resembling a planet yet lacking the necessary mass for stellar formation and includes objects like moons and minor planets not bound to a star
3. A celestial entity similar to a planet, which does not meet the criteria to be classified as a full planet and encompasses various bodies that may follow independent orbits in space

Etymology: Astronomers needed a name for objects that are too small to be stars yet too unlike ordinary planets to fit the usual categories, and "planemo" is a contraction of "planetary-mass object." The term was coined by Gibor Basri, a professor of astronomy at the University of California, Berkeley, at a 2003 conference of the International Astronomical Union, the body that sets the official rules for naming and classifying celestial objects. The word's logic is simply in its shortening. The full phrase names the defining property, a mass comparable to a planet's, and the "-mo" ending is a clipped form of "-mass object" squeezed into a single pronounceable word. Because the term describes mass rather than location, it covers bodies that orbit a star, those that drift freely between stars, and those that are moons. That is why the meaning includes objects that are not bound to any star at all.

Synonyms: planetary mass, substellar object