planetary

Planetary is an adjective meaning related to planets. It is used in astronomy and related fields to describe objects, processes, or phenomena associated with planets. The word derives from Latin planetaryus, itself from Greek planetes, meaning "wanderer."

In science, planetary science is the study of planets, their moons, rings, atmospheres, surfaces, interiors, formation, and evolution. It encompasses bodies in our Solar System as well as exoplanets orbiting other stars.

Related subfields include planetary geology, which focuses on a planet's or moon's surface and interior structure, and planetary atmospheres, which studies atmospheric composition, dynamics, and climate. The concept of planetary habitability addresses the potential for life-supporting conditions on planets or moons.

Planetary nebula is a historical misnomer for a class of glowing shells formed by dying low- to intermediate-mass stars. The name reflects early Saturn-like appearances, not planets.

Outside astronomy, planetary is used in engineering to describe gear systems called planetary gears, and in sustainability to refer to planetary boundaries—thresholds that constrain Earth system processes.