How do rogue planets become separated from their original star systems?

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Extrasolar planet Artist's conception of the extrasolar planet HD 209458b, some 150 light-years from Earth.

In astronomy, a rogue planet is a planetary-mass object that does not orbit a star but instead wanders freely through space.

Most rogue planets are believed to have been ejected from their original star systems due to gravitational encounters with other celestial bodies. These interactions can destabilize a planet's orbit, eventually forcing it out of the system entirely. While some rogue planets may form independently through the collapse and fragmentation of a molecular cloud core—similar to how stars form—the majority are thought to be "exiled" members of established systems.1

These objects are quite numerous, with estimates suggesting there are roughly six times as many rogue planets as there are planets that orbit stars within our galaxy.1