Planets outside of theSolar System have appeared infiction since at least the 1850s, long before the first real ones were discovered in the 1990s. Most of these fictional planets do not differ significantly from theEarth and serve only assettings for the narrative. The majority hostnative lifeforms, sometimes with humans integrated into the ecosystems. Fictional planets that are notEarth-like vary in many different ways. They may have significantly stronger or weakergravity on their surfaces, or have a particularly hot or cold climate. Bothdesert planets andocean planets appear, as do planets with unusual chemical conditions. Various peculiar planetary shapes have been depicted, includingflattened, cubic, andtoroidal. Some fictional planets exist inmultiple-star systems where the orbital mechanics can lead to exotic day–night orseasonal cycles, while othersdo not orbit any star at all. More fancifully, planets are occasionally portrayed as havingsentience, though this is less common than stars receiving the same treatment or a planet's lifeforms having a collective consciousness.
[S]ince information about extrasolar planets remains limited and incomplete, science fiction writers can freely imagine various sorts of alien worlds where their heroes might experience different sorts of adventures and encounter exoticaliens. Indeed, one activity associated withhard science fiction is "world building", meticulously crafting bizarre planets that nonetheless accord with all scientific laws.
Most extrasolar planets in fiction are similar toEarth—referred to in theStar Trek franchise asClass M planets—and serve only assettings for the narrative.[1][2] One reason for this, writesStephen L. Gillett [Wikidata] inThe Greenwood Encyclopedia of Science Fiction and Fantasy, is to enablesatire.[3] Nevertheless, there are also many fictional planets that differ significantly from Earth.[1][2][3]Earth-like planets have become less common in fiction following the first detection of anexoplanet around a Sun-like star in 1995,[a] reflecting the scarcity of such worlds among the thousands discovered since.[5][6] The majority of extrasolar planets in fiction are inhabited by native species,[4] and humans are variously depicted as being integrated into or remaining apart from such alien ecosystems.[7] Some fictional planets are described as orbiting real stars;[2][8] a 2024 article in theJournal of Science Communication analysed a sample of 142 fictional exoplanets, of which nearly a third fulfilled this criterion, and found "an absence of influence of whether or not the planet setting is in a real star system on other worldbuilding characteristics".[4]
Various exotic planetary shapes appear in fiction.[9] InHal Clement's 1953 novelMission of Gravity, the planetMesklin's rapid rotation causes it to be shaped roughly like a flat disk and gravity is consequently about 200 times weaker at the equator than it is at the poles,[1][9][10] while the moonJinx inLarry Niven's 1975 short story "The Borderland of Sol" is instead stretched bytidal forces from the planet it orbits rather than flattened, resulting in aprolate spheroid shape where the equator is covered by an atmosphere but the poles rise up above it.[11][12] Another disk-shaped planet is theDiscworld ofTerry Pratchett's 1983–2015fantasybook series of that name, aflat world which iscarried on the backs of elephants that are in turncarried on the back of a turtle, with the arrangementorbited by the world's sun.[1][13]Bizarro World in theSuperman franchise is acubic planet, rendered that shape by the actions of Superman.[1][9] Earth itself gets turned into a cube inHenry H. Gross's 1987 short story "Cubeworld", and an altogether artificial planet-sized cube is the setting ofG. David Nordley's 2009 novelTo Climb a Flat Mountain.[9]Double planets close enough together to share an atmosphere through theirRoche lobes appear inHomer Eon Flint's 1921 short story "The Devolutionist",Robert L. Forward's 1982 novelRocheworld (a.k.a.The Flight of the Dragonfly),Bob Shaw's 1986 novelThe Ragged Astronauts—which depicts an interplanetaryhot air balloon expedition—andCharles Sheffield's 1990 novelSummertide.[3][9][14][15] A planet in the shape of atorus is the setting of Flint's 1921 short story "The Emancipatrix", being the result of theprotoplanetary disk condensing so quickly that it did not coalesce into a spherical shape first; an artificial planet-sized torus also appears inJohn P. Boyd [Wikidata]'s 1981 short story "Moonbow", while Niven wrote of a much larger toroidalmegastructure in space in the 1970 novelRingworld and a much smaller one in the 1973 novelProtector.[9]Arthur C. Clarke's 1949 short story "The Wall of Darkness" is set on a planet bounded by a wall in the shape of anAlice handle, a kind of three-dimensional equivalent of aMöbius strip.[1][16]
Planets inmultiple star systems have attracted attention from science fiction writers, especially in terms ofwhat kind of life would exist on planets with more than one sun and howhistory might be cyclical as a result of the "long year" that occurs if theorbital period around one of the stars is very lengthy.[14][18][19] A particularly early example of this isC. I. Defontenay's 1854 novelStar ou Psi de Cassiopée (English title:Star: Psi Cassiopeia),[14] described byscience fiction editorDavid Pringle as "the first detailed evocation of an alien solar system",[20] which depicts variousalien species inhabiting the planets orbiting the stars.[14][21][22][23]Isaac Asimov's 1941 short story "Nightfall" portrays a planet which is in constant daylight from at least one of its six suns for millennia at a time before a single night of true darkness, which is a much-anticipated event;[18][24][25] the 1963The Twilight Zone episode "On Thursday We Leave for Home" depicts a planet that is challenging for humans to inhabit due to the unending heat and light from a pair of suns;[26] andMark Hodder's 2012 novelA Red Sun Also Rises is set on a planet where a dim red sun rises at the same time as the planet's twin white suns set.[18] Hal Clement's 1957 novelCycle of Fire depicts a planet in a binary star system where theseasons last for decades and different species dominate the hot and cold parts of the year,[1][14][19]Poul Anderson's 1974 novelFire Time portrays a planet where the majority of the surface becomes uninhabitable approximately once a millennium when it makes a close approach to one of its stars andmass migration of the native lifeforms ensues,[18] andBrian Aldiss's 1982–1985Helliconia trilogy is set on a planet where the orbital mechanics lead to century-long seasons and there are two distinctecosystems—one adapted to the short period around the closer star and another adapted to the long year around the more distant one.[1][3][18][19][27] A similar effect appears in Aldiss's 1977 short story "Creatures of Apogee", albeit here as a result of a highlyeccentric orbit around a single star where the distance to the star thus varies greatly between thenearest and farthest points in the orbit.[15] The 1985 anthologyMedea: Harlan's World is a collaborative effort betweenHarlan Ellison and several other science fiction writers consisting of several storiesset on the same planet in a multiple star system.[1][14] The 2002 television seriesFirefly is set in a system of five stars each orbited by its ownplanetary system, all close enough to each other to permit easy travel between the worlds.[18]
Planets that do not orbit any star, known asrogue planets, appear in several works.[14][28] In the 1977 novelDying of the Light byGeorge R. R. Martin, such a planet becomes a temporarytourist destination as it passes by a star before leaving the star's vicinity and becoming uninhabitable again.[14][29] Hal Clement's 1974 short story "The Logical Life" explores what kind of life could exist on a planet without a star,[29] while the 2002Star Trek: Enterprise episode "Rogue Planet" depicts how the lifeforms on a world of perpetual night might be exploited by outsiders.[28]
Earth is threatened by impact with a rogue planet in the 1933 novelWhen Worlds Collide byEdwin Balmer andPhilip Wylie andits 1951 film adaptation,[28] and it becomes a rogue planet itself inFritz Leiber's 1951 short story "A Pail of Air".[28][29] A rogue planet on a collision course with a star-orbiting planet also appears inNeil R. Jones's 1934 short story "The Sunless World", though here the rogue planet is the inhabited one.[14][30]
Portraying planets with conditions that differ significantly from Earth's in terms of physical environment has been a recurring practice since the middle of the 1900s.[3] Many of these stories imagine how indigenous lifeforms might be adapted to those conditions, withHal Clement andPoul Anderson being particularly prolific exponents of this craft.[7][12][31] The high gravity of Mesklin in Clement'sMission of Gravity thus results in its inhabitants having a centipede-like body structure,[1][9][31][32] while the low gravity yet dense atmosphere in Anderson's 1958 novelWar of the Wing-Men (a.k.a.The Man Who Counts) makes it possible for humanoid creatures to fly using their own wings.[1][3][31]Desert planets are common; astrophysicistElizabeth Stanway [Wikidata] posits that this is because the setting strikes the right balance between novelty and familiarity to most audiences, in addition to the relative inhospitality providing a survival aspect to the narrative.[33] One of the most prominent examples thereof isArrakis inFrank Herbert's 1965 novelDune, where the extreme scarcity of water influences all aspects of the planet's ecology and society.[1][3][32][33][34] Less extreme desert conditions are found on theStar Wars planetTatooine, with more plentiful and varied lifeforms as a result.[33] At the other end of the spectrum areplanets covered entirely by water, an early example of which appears in Neil R. Jones's 1933 short story "Into the Hydrosphere".[14][31]Joan Slonczewski's 1986 novelA Door into Ocean is a piece offeminist science fiction set on an ocean world with an all-female population,[1][3] whileUrsula K. Le Guin's 1969 novelThe Left Hand of Darkness is set on afrigid world of perpetual winter where the inhabitants do not have a fixed sex.[34][35][36] One of the planets in the 2014 filmInterstellar is covered by a shallow ocean and orbits so closely around ablack hole that there are both tidal waves the height of mountains and extremetime dilation.[35] Other fictional planets differ in their chemical rather than physical environment.Chlorine planets appear in Isaac Asimov's 1951 short story "C-Chute" and the 1976Space: 1999 episode "The AB Chrysalis",[26] whileC. J. Cherryh's 1988 novelCyteen depicts a planet dominated bysilicon-based life whosebiochemistry creates byproducts extremely hazardous to human health.[37]
Planets themselves being portrayed as alive, while relatively rare (especially compared to stars receiving the same treatment), is a recurring theme.[1][38] Sentient planets appear inRay Bradbury's 1951 short story "Here There Be Tygers",Stanisław Lem's 1961 novelSolaris, andTerry Pratchett's 1976 novelThe Dark Side of the Sun.[1][38]Ego the Living Planet is a recurring character inMarvel Comics.[38] The related concept known as theGaia hypothesis—an entireplanetary ecosphere functioning as a single organism, often but not always imbued with a planet-wideconsciousness—is more common; examples includeMurray Leinster's 1949 short story "The Lonely Planet", Isaac Asimov's 1982 novelFoundation's Edge, and the 2009 filmAvatar.[38][39][40]
The following are fictional extrasolar planets with stand-alone Wikipedia articles.
A pioneering account of life in the vicinity of Star, a world in a solar system that has three principal suns and a miniature sun that orbits Star along with four satellite planets. The multicolored light from these various sources has kaleidoscopic effects on the surface of Star, which is inhabited by variously sized humanoids whose history—involving forced migrations to its inhabited neighbors—is elaborately described.
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