planetarysystem

A planetary system is a gravitationally bound arrangement in which one or more planets orbit a star or stellar remnant. In most cases, the term refers to a star–planet system, though the gravitational influence of other bodies such as brown dwarfs, comets, and debris disks can shape its evolution.

The central star is often accompanied by a variety of other bodies, including planets of differing sizes (from terrestrial to gas giants), dwarf planets, moons, minor bodies like asteroids and comets, and circumstellar debris disks. Some planetary systems exhibit complex architectures such as resonant chains, coplanar multi-planet arrangements, or highly eccentric orbits.

Planetary systems form from rotating molecular clouds that collapse to form a central protostar surrounded by a protoplanetary disk. Through accretion and collisions, planetesimals grow into planets. Interactions and migration within the disk, as well as post-formation dynamical evolution, help determine the final layout.

Planets in such systems are detected by methods including transit observations (watching the star dim as a planet passes in front), radial velocity (measuring stellar wobbles due to gravity), direct imaging, and gravitational microlensing. Characterizing planetary systems reveals a wide diversity, from compact, resonant multi-planet systems to wide or solitary gas giants.

As of the 2020s, thousands of exoplanets in hundreds of planetary systems have been confirmed, indicating that such systems are common in the galaxy. Ongoing surveys aim to assess their formation, dynamics, and potential habitability.