Rogue planet

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This article is about a type of astronomical object. For other uses, see Rogue planet (disambiguation).

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, S Ori 70), but those detections remain unconfirmed.[1]

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.

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[edit] Retention of heat in interstellar space

In 1998, David J. Stevenson authored a paper entitled "Possibility of Life Sustaining Planets in Interstellar Space."[2] 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.[3] 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.[2] 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, providing a geodynamo-created protective magnetosphere and possible sea floor volcanism which could provide an energy source for life.[2] 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.

A study of simulated planet ejection scenarios has suggested that around five percent of Earth-sized planets with Moon-sized moons would retain their moons after ejection. A large moon would be a source of significant geological tidal heating.[4]

[edit] 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.

[edit] Interstellar planets in popular culture

In Phillip Wylie's When Worlds Collide (1932), Earth is first devastated, and then destroyed by "Bronson Alpha", a gas giant-sized rogue planet, orbited by "Bronson Beta", an earth-sized satellite. Fortunately, advance warning enables several groups of survivors to escape to Bronson Beta, whose orbit maps onto that of the destroyed Earth, and is torn away from its former primary by the gravitational impact of the Bronson Alpha/Earth collision. In the 1951 cinematic incarnation, Bronson Alpha was renamed "Bellus", while Bronson Beta was designated "Zyra."

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" (which might be a black hole or cool brown dwarf), it shares many characteristics with an interstellar planet.

The first known use of "rogue planet" as term for such detached worlds occurred in Poul Anderson's 1969 Polesotechnic League novel Satan's World.

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 Star Trek: Enterprise episode "Rogue Planet", 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.

The Red Star, in Anne McCaffrey's Dragonriders of Pern series, was a rogue planet that was captured by Rukbat, the star.

In the Dr Who episode The Tenth Planet, Mondas, home of the Cybermen, was reported as being knocked out of Solar orbit during prehistoric times and then returning in 1986. In the episode Revenge of the Cybermen, the Cybermen waged war on the inhabitants of a rogue planetoid, the remnants of the destroyed planet Voga.

In the video game Metroid Prime 2: Echoes, the planet Samus visits, Aether, is a rogue planet.

In the Red Dwarf books, the Earth becomes a rogue planet when it is torn from its orbit by exploding sewage.

In just about every continuity, the Transformers' homeworld of Cybertron is considered a rogue planet.

[edit] References

  1. ^ Rogue planet find makes astronomers ponder theory
  2. ^ a b c Stevenson, David J. (1998). "Possibility of Life-Sustaining Planets in Interstellar Space". Nature. 
  3. ^ Lissauer, J.J. (1987). "Timescales for Planetary Accretion and the Structure of the Protoplanetary disk". Icarus 69: 249-265. doi:10.1016/0019-1035(87)90104-7. 
  4. ^ Debes, John H.; Steinn Sigurðsson (October 20 2007). "The Survival Rate of Ejected Terrestrial Planets with Moons". The Astrophysical Journal 668: L167-L170. 

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