A rogue planet is a planet not orbiting a star and thus not being part of a solar system. However, such planets might support life due to geologic activities. The Founders' homeworld in the Omarion Nebula was such a planet, as was Dakala and Trelane's planet of Gothos. (ENT: "Rogue Planet"; DS9: "The Search, Part I"; TOS: "The Squire of Gothos").

Rogue planets do actually exist in the universe. A rogue planet is an object which has equivalent mass to a planet and is not gravitationally bound to any star, and that therefore moves through space as an independent object. Several astronomers claim to have detected such objects (for example, Cha 110913-773444), but those detections remain unconfirmed.

Some astronomers refer to these objects as "planets", usually because they believe such objects were planets that were ejected from orbit around a star. However, others believe that the definition of 'planet' should depend on current observable state, and not origin. Additionally, these objects may form on their own through gas cloud collapse similar to star formation; in which case they would never have been planets.

In 1998, David J. Stevenson's "Possibility of Life Sustaining Planets in Interstellar Space theorized that some wandering objects, that Stevenson refers to as "planets", drift in the vast expanses of cold interstellar space and could possibly sustain a thick atmosphere which would not freeze out due to radiative heat loss. He proposes that atmospheres are preserved by the pressure-induced far infrared radiation opacity of a thick hydrogen-containing atmosphere. It is thought that during planetary system formation, several small protoplanetary bodies may be ejected from the forming system. With the reduced ultraviolet light associated with its increasing distance from the parent star, the planet's predominantly hydrogen and helium containing atmosphere would be easily confined even by an Earth-sized body's gravity.