Planetet

Planetet is a term used in speculative discussions and some science fiction to denote a small planetary body that sits between the largest asteroids and the smallest true planets in size and mass. It is not part of official planetary taxonomy; major space agencies and the International Astronomical Union do not recognize a category named planetet.

In proposed schemes, planetets have a range of diameters from roughly tens to a few thousand kilometers. They may be spherical if their self-gravity is sufficient, otherwise irregular. Depending on composition, they might retain volatile ices, and some could possess very thin atmospheres. Surfaces vary from rocky and pitted to icy and cratered.

Orbits: Planetets orbit stars as independent bodies or as satellites of larger objects in some scenarios. They may reside in asteroid belts, the Kuiper belt, or more distant exoplanetary systems. Because their masses are typically below the threshold needed to clear neighboring material, they do not meet the conventional definition of a planet.

Formation and observations: Planetets are conceived as products of planetesimal accretion that halt growth before forming a full planet, due to dynamical perturbations or limited material. In exoplanet surveys, candidates with modest masses and small radii are occasionally discussed informally as planetets, but such use is not standardized. The term remains mainly a speculative or fictional descriptor rather than a formal scientific category.