Talk:Rogue planet/Pre-merge

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, 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 orbiting 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 like stars; in which case they would never have been planets.

Atmosphere hypothesis
In 1998, David J. Stevenson authored a paper entitled "Possibility of Life Sustaining Planets in Interstellar Space." In this paper, Stevenson theorizes 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.

It is calculated that for an Earth-sized object at a kilobar hydrogen atmospheric pressures in which a convective gas adiabat has formed, geothermal energy from residual core radioisotope decay will be sufficient to heat the surface to temperatures above the melting point of water. Thus, it is proposed that interstellar planetary bodies with extensive liquid water oceans may exist. It is further suggested that the bodies are likely to remain geologically active for long periods of time, providing a geodynamo-created protective magnetosphere and possible sea floor volcanism which could provide an energy source for life. The author admits these bodies will be difficult to detect due to the intrinsically weak thermal microwave radiation emissions emanating from the lower reaches of the atmosphere.

Proplyds of planetars?
Recently, it has been discovered that some extrasolar planets such as the planemo 2M1207b, orbiting the brown dwarf 2M1207, have debris discs. If some large interstellar objects are considered as stars (brown sub-dwarfs) then the debris could coalesce into planets, meaning the disks are proplyds. If these are considered planets, then the debris would coalesce as moons. The term planetar exists for those accretion masses that seem to fall between stars and planets.

Interstellar planets in popular culture
The short story A Pail of Air by Fritz Leiber, which first appeared on the radio show X Minus One in March 1956, is narrated by a boy living on Earth after it has been torn from the Sun's gravity and captured by a passing "dark star". Although Earth now orbits this "dark star", it shares many characteristics with an interstellar planet.

The homeworld of the Founders in Star Trek: Deep Space Nine is a rogue planet in a nebula; it has climatic conditions capable of supporting humanoid life.

In the episode Rogue Planet of Star Trek: Enterprise, Enterprise happens upon a rogue planet with an earth-like atmosphere. The planet was heated by volcanic vents that sent heat into the atmosphere, thus sustaining the ecology of the planet.

In the Warhammer 40,000 universe, the Temple of the Culexus Assassins of the Officio Assassinorum is located deep under the surface of a 'dead' rogue planet.

The planet Zonama Sekot in the Star Wars fictional universe was first introduced in the novel Rogue Planet and later expanded on in the New Jedi Order series. The planet, which is in fact a sentient life form itself, is home to life unlike any other in the galaxy, including organic spaceships.

In Space 1999 the Earth's Moon is knocked out of orbit by an explosion at its nuclear waste dump. The Moon then becomes a wandering planet.

The rogue planet of Worlorn is the scene of action in George R. R. Martin’s novel Dying of the Light.