Planetarycentric

Planetarycentric is an adjective used in astronomy and spaceflight to describe reference frames, coordinate systems, or models in which a planet acts as the central body. In practice, planetarycentric (often written as planet-centric or planet-centered in some sources) denotes measurements or calculations that take the planet’s center of mass as the origin or primary gravitational influence.

In celestial mechanics and mission analysis, planetarycentric frames are used to describe the motion of natural satellites or spacecraft around a given planet. Orbital elements, state vectors, and trajectories are often defined with the planet at the origin and with the planet’s equatorial plane or gravity field serving as reference. This frame is convenient for studying moons, ring systems, and close-in dynamics, where the planet dominates the gravitational environment and perturbations from other bodies are treated as secondary effects.

Planetarycentric is distinct from related frames such as barycentric (center of mass of a system), heliocentric or geocentric (Sun- or Earth-centered, respectively). The term is sometimes used interchangeably with planet-centric or planet-centered, though some literature reserves “planetocentric” for coordinate systems and mappings tied to a planet’s interior surface or geographic coordinates, and uses “planetary-centric” for dynamics-focused applications. In all cases, the choice of frame affects how positions and velocities are described and how perturbations are modeled.

See also: barycentric coordinates, geocentric coordinate system, heliocentric coordinate system, planetocentric coordinates.