= Planetary system
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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