Planetstar

Planetstar is a term that appears in speculative literature and informal discourse but is not an established category in astronomy. It is used to describe objects that blend planetary and stellar properties, either as a planet‑mass body that temporarily exhibits star‑like luminosity or as a body near the planet–brown dwarf boundary with unusual energy output. There is no single, accepted definition.

Etymologywise, planetstar is a portmanteau of planet and star. In most usages, the term implies a spectrum of intermediate properties, with meanings varying by author. Some writers imagine a planet with an unusually hot, bright surface or atmosphere, while others refer to objects in a mass regime where brief fusion could occur but long‑term sustaining fusion does not take place.

In real-world astronomy, the closest analogues are brown dwarfs, hot‑start planets, and self‑luminous young planets. The distinction between planet and substellar object is typically drawn by mass and the presence or absence of sustained nuclear fusion. Observationally, researchers rely on luminosity, spectral features, and atmospheric composition. A true “planetstar” designation is not used in standard catalogs or classifications.

In fiction and thought experiments, planetstars often function as a device to explore extreme environments, unusual energy budgets, or novel habitability scenarios. They provide a way to consider how planetary atmospheres and surfaces would respond to sustained, star‑like energy input or to discuss formation pathways under intense radiation.

See also: brown dwarf, exoplanet, star–planet interaction.