A planetary system consists of planets and associated smaller bodies orbiting a star or stellar multiple. Satellites, rings, debris and residual gas can contribute to its dynamics even when only the planets are easily observed.
The bodies interact gravitationally rather than following permanently independent ellipses. Orbital resonances, close encounters and tidal evolution can change their arrangement. Observations also sample different components: transit measurements constrain projected geometry and radius ratios, while stellar radial velocities constrain masses through the system's reflex motion. Combining such measurements provides a more complete description than counting detected planets alone.
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A planetary system refers to a collection of celestial bodies that are bound together by gravitational forces and orbit a central star or stars. The most familiar example of a planetary system is our own Solar System, which includes the Sun as the central star and eight planets, along with their moons, dwarf planets, asteroids, comets, and other objects.
