Rogue planet

A planetary-mass object that travels through space without orbiting a star. It may form in isolation or be ejected from a planetary system.

Planetary system formation: The processes by which stars and their surrounding disks develop into systems of planets and smaller bodies. Planet formation sets the stage for systems that can later eject planets.
Gravitational microlensing: A temporary brightening of a distant source when a foreground object's gravity bends its light. A rogue planet can reveal itself by lensing a background star despite emitting little light.
PSO J318.5−22: A young, directly imaged planetary-mass object that is not known to orbit a star. Its infrared glow made it a prominent example of an isolated planetary-mass object.
Brown dwarf: A substellar object too low in mass to sustain ordinary hydrogen fusion in its core. Brown dwarfs overlap rogue planets in mass, but their formation histories can differ.
Molecular cloud: A cold, dense interstellar cloud of gas and dust where stars and some substellar objects form. Some rogue planets may form directly as fragments within collapsing clouds.
Einstein radius: The characteristic angular scale of gravitational lensing set by the lens and source distances and lens mass. Microlensing event duration depends partly on the small Einstein radius of a planetary-mass lens.
OTS 44: A young, low-mass object in the Chamaeleon I region, surrounded by a disk of gas and dust. Its disk suggests that planet-like objects can form in isolation.
Exoplanet: A planet orbiting a star beyond the Solar System. Rogue planets are planetary-mass objects outside the usual star-orbiting exoplanet category.
Gravitational scattering: A change in an object's orbit caused by gravitational encounters with other bodies. Close encounters among young planets can fling one out of its system.
Parallax (astronomy): An apparent change in an object's position or lensing signal caused by observing from separated locations. Parallax measurements can help determine a microlens's distance and mass.

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