Free-floating planet

A planetary-mass object that is not gravitationally bound to a star. It may form in isolation or be ejected from a planetary system.

Dynamical ejection: The gravitational expulsion of an object from a bound system through interactions with other bodies. Close encounters among planets can eject a planet from its system.
Planetary-mass object: An astronomical object with a mass comparable to that of planets, regardless of whether it orbits a star. The broader category includes both free-floating and star-orbiting objects.
Gravitational microlensing: The temporary magnification of a background source when a foreground mass bends its light. Microlensing can detect isolated masses without requiring their own detectable light.
Substellar object: An astronomical object less massive than a star, including brown dwarfs and planetary-mass bodies. Free-floating planets occupy the least massive, most classification-sensitive end of this category.
Cloud fragmentation: The breakup of a collapsing gas cloud into separate self-gravitating objects. Some free-floating planets may form directly when small cloud fragments collapse.
Gravitational binding: The condition in which gravity keeps an object or system bound against escape. The defining distinction is whether the object remains bound to a star.
Direct imaging: The detection of an astronomical object by collecting light emitted or reflected by the object itself. Infrared imaging can reveal nearby, young free-floating planets while they remain warm.
Planetary formation: The processes by which planets form from material around young stars. A central question is how many free-floating planets formed in disks before ejection.
Gravitational instability: The collapse of dense regions in a self-gravitating disk or cloud under their own gravity. Instability in a circumstellar disk can produce objects later scattered away.
Mass–luminosity relation: The relationship between an object's mass and its emitted luminosity, which depends on its physical state and age. Without starlight, mass estimates rely on models of how these objects cool and fade.

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