62-483: Tralfamadore is the name of a fictional planet appearing in the novels of Kurt Vonnegut in inconsistently described variations. It is variously depicted as being located outside of the Milky Way galaxy or being fictional within the fiction itself . Tralfamadore's inhabitants are described inconsistently across different works. Robert Tally compared this to Vonnegut's habit of (re-)introducing characters that have
124-430: A terrestrial planet and there have been several scientific studies aimed at finding such planets. Often implied but not limited to are such criteria as planet size, surface gravity, star size and type (i.e. Solar analog ), orbital distance and stability, axial tilt and rotation, similar geography , oceans , air and weather conditions, strong magnetosphere and even the presence of Earth-like complex life . If there
186-455: A 2024 article in the Journal 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". Various exotic planetary shapes appear in fiction. In Hal Clement 's 1953 novel Mission of Gravity ,
248-575: A centipede-like body structure, while the low gravity yet dense atmosphere in Anderson's 1958 novel War of the Wing-Men ( a.k.a. The Man Who Counts ) makes it possible for humanoid creatures to fly using their own wings. Desert planets are common; astrophysicist Elizabeth Stanway [ Wikidata ] posits that this is because the setting strikes the right balance between novelty and familiarity to most audiences, in addition to
310-591: A hundred quintillion Earth-like planets. This would correspond to around 20 earth analogs per square centimeter of the Earth. In 2013, a Harvard–Smithsonian Center for Astrophysics using statistical analysis of additional Kepler data suggested that there are at least 17 billion Earth-sized planets in the Milky Way. This, however, says nothing of their position in relation to the habitable zone. A 2019 study determined that Earth-size planets may circle 1 in 6 Sun-like stars. Terraforming (literally, "Earth-shaping") of
372-553: A much larger toroidal megastructure in space in the 1970 novel Ringworld and a much smaller one in the 1973 novel Protector . Arthur C. Clarke 's 1949 short story " The Wall of Darkness " is set on a planet bounded by a wall in the shape of an Alice handle , a kind of three-dimensional equivalent of a Möbius strip . Planets in multiple star systems have attracted attention from science fiction writers, especially in terms of what kind of life would exist on planets with more than one sun and how history might be cyclical as
434-410: 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 and mass migration of the native lifeforms ensues, and Brian Aldiss 's 1982–1985 Helliconia trilogy is set on a planet where the orbital mechanics lead to century-long seasons and there are two distinct ecosystems —one adapted to the short period around
496-414: A result of the "long year" that occurs if the orbital period around one of the stars is very lengthy. A particularly early example of this is C. I. Defontenay 's 1854 novel Star ou Psi de Cassiopée (English title: Star: Psi Cassiopeia ), described by science fiction editor David Pringle as "the first detailed evocation of an alien solar system", which depicts various alien species inhabiting
558-486: A solar candidate, Kepler-452b , was announced. On 11 January 2023, NASA scientists reported the detection of LHS 475 b , an Earth-like exoplanet - and the first exoplanet discovered by the James Webb Space Telescope . The probability of finding an Earth analog depends mostly on the attributes that are expected to be similar, and these vary greatly. Generally it is considered that it would be
620-409: A temporary tourist destination as it passes by a star before leaving the star's vicinity and becoming uninhabitable again. Hal Clement's 1974 short story " The Logical Life " explores what kind of life could exist on a planet without a star, while the 2002 Star Trek: Enterprise episode " Rogue Planet " depicts how the lifeforms on a world of perpetual night might be exploited by outsiders. Earth
682-683: Is " world building ," meticulously crafting bizarre planets that nonetheless accord with all scientific laws. Gary Westfahl , Science Fiction Literature through History: An Encyclopedia (2021), "Alien Worlds" entry Most extrasolar planets in fiction are similar to Earth —referred to in the Star Trek franchise as Class M planets —and serve only as settings for the narrative. One reason for this, writes Stephen L. Gillett [ Wikidata ] in The Greenwood Encyclopedia of Science Fiction and Fantasy ,
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#1732791393855744-518: Is a chance that serendipitous events may have allowed an Earth-like planet to form elsewhere that would allow the emergence of complex, multi-cellular life. In contrast, the Rare Earth hypothesis asserts that if the strictest criteria are applied, such a planet, if it exists, may be so far away that humans may never locate it. Because the Solar System proved to be devoid of an Earth analog,
806-444: Is complex life, there could be some forests covering much of the land. If there is intelligent life, some parts of land could be covered in cities . Some factors that are assumed of such a planet may be unlikely due to Earth's own history. For instance, the Earth's atmosphere was not always oxygen-rich and this is a biosignature from the emergence of photosynthetic life. The formation, presence, influence on these characteristics of
868-543: Is covered by an atmosphere but the poles rise up above it. Another disk-shaped planet is the Discworld of Terry Pratchett 's 1983–2015 fantasy book series of that name , a flat world which is carried on the backs of elephants that are in turn carried on the back of a turtle , with the arrangement orbited by the world's sun . Bizarro World in the Superman franchise is a cubic planet, rendered that shape by
930-500: Is expected to continue burning for 12 trillion years (compared to the Suns remaining 5 billion year lifetime) which is time enough for life to arise by abiogenesis . For comparison, life evolved on Earth in a mere one billion years. The concept of the habitable zone (or Liquid Water Zone) defining a region where water can exist on the surface, is based on the properties of both the Earth and Sun. Under this model, Earth orbits roughly at
992-452: Is of particular interest to astrobiologists and astronomers under reasoning that the more similar a planet is to Earth, the more likely it is to be capable of sustaining complex extraterrestrial life . As such, it has long been speculated and the subject expressed in science , philosophy , science fiction and popular culture . Advocates of space colonization and space and survival have long sought an Earth analog for settlement. In
1054-438: Is often thought to be a significant factor, as planets of Earth's size are thought more likely to be terrestrial in nature and be capable of retaining an Earth-like atmosphere. The list includes planets within the range of 0.8–1.9 Earth masses, below which are generally classed as sub-Earth and above classed as super-Earth . In addition, only planets known to fall within the range of 0.5–2.0 Earth radius (between half and twice
1116-538: Is the inhabited one. 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. Many of these stories imagine how indigenous lifeforms might be adapted to those conditions, with Hal Clement and Poul Anderson being particularly prolific exponents of this craft. The high gravity of Mesklin in Clement's Mission of Gravity thus results in its inhabitants having
1178-578: Is threatened by impact with a rogue planet in the 1933 novel When Worlds Collide by Edwin Balmer and Philip Wylie and its 1951 film adaptation , and becomes a rogue planet itself in Fritz Leiber 's 1951 short story " A Pail of Air ". A rogue planet on a collision course with a star-orbiting planet also appears in Neil R. Jones 's 1934 short story " The Sunless World ", though here the rogue planet
1240-580: Is to enable satire . Nevertheless, there are also many fictional planets that differ significantly from Earth. Earth-like planets have become less common in fiction following the first detection of an exoplanet around a Sun-like star in 1995, reflecting the scarcity of such worlds among the thousands discovered since. The majority of extrasolar planets in fiction are inhabited by native species, and humans are variously depicted as being integrated into or remaining apart from such alien ecosystems. Some fictional planets are described as orbiting real stars;
1302-406: Is used. Each of these temperatures is affected by climate, which is influenced by the orbit and rotation (or tidal locking) of the planet, each of which introduces further variables. Below is a comparison of the confirmed planets with the closest known temperatures to Earth. Another criterion of an ideal life-harboring earth analog is that it should orbit a solar analog ; that is, a star much like
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#17327913938551364-656: The Earth , and serve only as settings for the narrative. The majority host native lifeforms , sometimes with humans integrated into the ecosystems. Fictional planets that are not Earth-like vary in many different ways. They may have significantly stronger or weaker gravity on their surfaces , or have a particularly hot or cold climate. Both desert planets and ocean planets appear, as do planets with unusual chemical conditions. Various peculiar planetary shapes have been depicted, including flattened , cubic, and toroidal . Some fictional planets exist in multiple-star systems where
1426-600: The Mariner (1965) and Viking space probes (1975–1980), however, revealed the planet as a barren cratered world. However, with continuing discoveries, other Earth comparisons remained. For example, the Mars Ocean Hypothesis had its origins in the Viking missions and was popularised during the 1980s. With the possibility of past water, there was the possibility that life could have begun on Mars, and it
1488-525: The Moon (such as tidal forces ) may also pose a problem in finding an Earth analog. The process of determining Earth analogs often involves reconciling several registers of uncertainty quantification . As anthropologist Vincent Ialenti 's work on the epistemology of analogical reasoning has shown, some planetary scientists are "more comfortable making the leap of faith to bridge time and space and pull together two disparate objects" than others are. Size
1550-528: The Universe , while the Rare Earth hypothesis suggests that they are extremely rare. The thousands of exoplanetary star systems discovered so far are profoundly different from the Solar System , supporting the Rare Earth Hypothesis. On 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in
1612-474: The habitable zones of Sun-like stars and red dwarf stars within the Milky Way Galaxy . The nearest such planet could be expected to be within 12 light-years of the Earth , statistically. In September 2020, astronomers identified 24 superhabitable planets (planets better than Earth) contenders, from among more than 4000 confirmed exoplanets , based on astrophysical parameters , as well as
1674-466: The natural history of known life forms on the Earth. On 11 January 2023, NASA scientists reported the detection of LHS 475 b , an Earth-like exoplanet — and the first exoplanet discovered by the James Webb Space Telescope . Scientific findings since the 1990s have greatly influenced the scope of the fields of astrobiology , models of planetary habitability and the search for extraterrestrial intelligence (SETI). Between 1858 and 1920, Mars
1736-400: The 1960s as the first space probes gathered more accurate scientific data on the planet and found that Venus is a very hot world with the surface temperature around 462 °C (864 °F) under an acidic atmosphere with a surface pressure of 9.2 MPa (1,330 psi). From 2004, Cassini–Huygens began to reveal Saturn's moon Titan to be one of the most Earth-like worlds outside of
1798-628: The 1976 Space: 1999 episode " The AB Chrysalis ", while C. J. Cherryh 's 1988 novel Cyteen depicts a planet dominated by silicon-based life whose biochemistry creates byproducts extremely hazardous to human health. Planets themselves being portrayed as alive, while relatively rare (especially compared to stars receiving the same treatment), is a recurring theme. Sentient planets appear in Ray Bradbury 's 1951 short story " Here There Be Tygers ", Stanisław Lem 's 1961 novel Solaris , and Terry Pratchett 's 1976 novel The Dark Side of
1860-426: The 2009 film Avatar . The following are fictional extrasolar planets with stand-alone Misplaced Pages articles. Earth analog An Earth analog , also called an Earth analogue , Earth twin , or second Earth , is a planet or moon with environmental conditions similar to those found on Earth . The term Earth-like planet is also used, but this term may refer to any terrestrial planet . The possibility
1922-661: The Dragonfly ), Bob Shaw 's 1986 novel The Ragged Astronauts —which depicts an interplanetary hot air balloon expedition—and Charles Sheffield 's 1990 novel Summertide . A planet in the shape of a torus is the setting of Flint's 1921 short story " The Emancipatrix ", being the result of the protoplanetary disk condensing so quickly that it did not coalesce into a spherical shape first; an artificial planet-sized torus also appears in John P. Boyd [ Wikidata ] 's 1981 short story " Moonbow ", while Niven wrote of
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1984-567: The Goldilocks position with substantial atmospheres may possess oceans and water clouds like those on Earth. In addition to surface water, a true Earth analog would require a mix of oceans or lakes and areas not covered by water, or land . Some argue that a true Earth analog must not only have a similar position of its planetary system but also orbit a solar analog and have a near circular orbit such that it remains continuously habitable like Earth. The mediocrity principle suggests that there
2046-496: The Kepler Mission suggested that between 1.4% and 2.7% of all Sun-like stars are expected to have Earth-size planets within the habitable zones of their stars. This means there could be as many as two billion Earth-sized planets in the Milky Way galaxy alone, and assuming that all galaxies have number of such planets similar to the Milky Way, in the 50 billion galaxies in the observable universe , there may be as many as
2108-609: The Milky Way and the larger universe is still unknown. It ranges from the extreme Rare Earth hypothesis estimates – one (i. e., Earth) – to innumerable. Several current scientific studies, including the Kepler mission , are aimed at refining estimates using real data from transiting planets. A 2008 study by astronomer Michael Meyer from the University of Arizona of cosmic dust near recently formed Sun-like stars suggests that between 20% and 60% of solar analogs have evidence for
2170-632: The Sun . Ego the Living Planet is a recurring character in Marvel Comics . The related concept known as the Gaia hypothesis —an entire planetary ecosphere functioning as a single organism, often but not always imbued with a planet-wide consciousness —is more common; examples include Murray Leinster 's 1949 short story " The Lonely Planet ", Isaac Asimov's 1982 novel Foundation's Edge , and
2232-567: The Sun. However, this criterion may not be entirely valid as many different types of stars can provide a local environment hospitable to life. For example, in the Milky Way , most stars are smaller and dimmer than the Sun. One such star, TRAPPIST-1 , is located 12 parsecs (39 light years) away and is roughly 10 times smaller and 2,000 times dimmer than the Sun, yet it harbors at least six Earth-like planets in its habitable zone . While these conditions may seem unfavorable to known life, TRAPPIST-1
2294-500: The Tralfamadorians with their deeper insights into "the science of nature [...] was Vonnegut's way of telling readers that humans don't know enough about each other and other life forms." Fictional planet Planets outside of the Solar System have appeared in fiction 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
2356-595: The actions of Superman. Earth itself gets turned into a cube in Henry H. Gross 's 1987 short story " Cubeworld ", and an altogether artificial planet-sized cube is the setting of G. David Nordley 's 2009 novel To Climb a Flat Mountain . Double planets close enough together to share an atmosphere through their Roche lobes appear in Homer Eon Flint 's 1921 short story " The Devolutionist ", Robert L. Forward 's 1982 novel Rocheworld ( a.k.a. The Flight of
2418-428: The centre of this zone or in the "Goldilocks" position. Earth is the only planet currently confirmed to possess large bodies of surface water. Venus is on the hot side of the zone while Mars is on the cold side. Neither are known to have persistent surface water, though evidence exists that Mars did have in its ancient past, and it is speculated that the same was the case for Venus. Thus extrasolar planets (or moons) in
2480-577: The closer star and another adapted to the long year around the more distant one. A similar effect appears in Aldiss's 1977 short story " Creatures of Apogee ", albeit here as a result of a highly eccentric orbit around a single star where the distance to the star thus varies greatly between the nearest and farthest points in the orbit . The 1985 anthology Medea: Harlan's World is a collaborative effort between Harlan Ellison and several other science fiction writers consisting of several stories set on
2542-413: The examples of Sirens of Titan and Slaughterhouse-Five , described the different Tralfamadorian races themselves as "tiny-minded smartasses" rendered impotent by their fatalistic worldview. Vonnegut scholar Julia A. Whitehead saw the overall concept of Tralfamadore throughout the author's work as in "many ways [...] his own Eden", an escapist imagined home of happier beings. In her view the presentation of
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2604-421: The far future, humans might artificially produce an Earth analog by terraforming . Before the scientific search for and study of extrasolar planets , the possibility was argued through philosophy and science fiction. Philosophers have suggested that the size of the universe is such that a near-identical planet must exist somewhere. The mediocrity principle suggests that planets like Earth should be common in
2666-515: The formation of rocky planets , not unlike the processes that led to those of Earth. Meyer's team found discs of cosmic dust around stars and sees this as a byproduct of the formation of rocky planets. In 2009, Alan Boss of the Carnegie Institution for Science speculated that there could be 100 billion terrestrial planets just in the Milky Way galaxy. In 2011 NASA's Jet Propulsion Laboratory (JPL), based on observations from
2728-404: The habitable zone from 2011. Though the technology provided a more effective means for detecting and confirming planets, it was unable to conclude definitively how Earth-like the candidate planets actually are. In 2013, several Kepler candidates less than 1.5 Earth radii were confirmed orbiting in the habitable zone of stars. It was not until 2015 that the first near-Earth sized candidate orbiting
2790-445: The habitable zone. Though having a dramatically different chemical makeup, discoveries such as the confirmation of Titanian lakes , rivers and fluvial processes in 2007, advanced comparisons to Earth. Further observations, including weather phenomena, have aided the understanding of geological processes that may operate on Earth-like planets. The Kepler space telescope began observing the transits of potential terrestrial planets in
2852-477: The inhabitants do not have a fixed sex. One of the planets in the 2014 film Interstellar is covered by a shallow ocean and orbits so closely around a black hole that there are both tidal waves the height of mountains and extreme time dilation . Other fictional planets differ in their chemical rather than physical environment. Chlorine planets appear in Isaac Asimov's 1951 short story " C-Chute " and
2914-626: The orbital mechanics can lead to exotic day–night or seasonal cycles, while others do not orbit any star at all . More fancifully, planets are occasionally portrayed as having sentience , 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 exotic aliens . Indeed, one activity associated with hard science fiction
2976-551: The other end of the spectrum are planets covered entirely by water , an early example of which appears in Neil R. Jones's 1933 short story " Into the Hydrosphere ". Joan Slonczewski 's 1986 novel A Door into Ocean is a piece of feminist science fiction set on an ocean world with an all-female population, while Ursula K. Le Guin 's 1969 novel The Left Hand of Darkness is set on a frigid world of perpetual winter where
3038-468: The planet Mesklin '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, while the moon Jinx in Larry Niven 's 1975 short story " The Borderland of Sol " is instead stretched by tidal forces from the planet it orbits rather than flattened, resulting in a prolate spheroid shape where the equator
3100-406: The planets orbiting the stars. 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, the 1963 The Twilight Zone episode " On Thursday We Leave for Home " depicts a planet that is challenging for humans to inhabit due to
3162-433: The probable frequency and distribution of Earth-like planets. Another criterion often cited is that an Earth analog must be terrestrial, that is, it should possess a similar surface geology—a planetary surface composed of similar surface materials. The closest known examples are Mars and Titan and while there are similarities in their types of landforms and surface compositions, there are also significant differences such as
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#17327913938553224-464: The radius of the Earth) are included. According to the size criteria, the closest planetary mass objects by known radius or mass are: This comparison indicates that size alone is a poor measure, particularly in terms of habitability . Temperature must also be considered as Venus and the planets of Alpha Centauri B (discovered in 2012), Kepler-20 (discovered in 2011 ), COROT-7 (discovered in 2009) and
3286-528: The relative inhospitality providing a survival aspect to the narrative. One of the most prominent examples thereof is Arrakis in Frank Herbert 's 1965 novel Dune , where the extreme scarcity of water influences all aspects of the planet's ecology and society. Less extreme desert conditions are found on the Star Wars planet Tatooine , with more plentiful and varied lifeforms as a result. At
3348-408: The same names as characters in previous works, but where the details do not match. Tally concluded that Vonnegut—unlike e.g. J. R. R. Tolkien —was not interested in creating an internally consistent fictional universe across his oeuvre, but content with a broad-strokes approach. A recurring characteristic of the inhabitants of Tralfamadore is their low esteem of humanity. Brian Stableford, considering
3410-467: The same planet in a multiple star system. The 2002 television series Firefly is set in a system of five stars each orbited by its own planetary system , all close enough to each other to permit easy travel between the worlds. Planets that do not orbit any star, known as rogue planets , appear in several works. In the 1977 novel Dying of the Light by George R. R. Martin , such a planet becomes
3472-431: The search has widened to extrasolar planets . Astrobiologists assert that Earth analogs would most likely be found in a stellar habitable zone , in which liquid water could exist, providing the conditions for supporting life. Some astrobiologists, such as Dirk Schulze-Makuch , estimated that a sufficiently massive natural satellite may form a habitable moon similar to Earth. The frequency of Earth-like planets in both
3534-408: The surface, past or present liquid water and life forms . There are several factors that can determine planetary temperatures and therefore several measures that can draw comparisons to that of the Earth in planets where atmospheric conditions are unknown. Equilibrium temperature is used for planets without atmospheres. With atmosphere, a greenhouse effect is assumed. Finally, surface temperature
3596-436: The temperature and quantities of ice. Many of Earth's surface materials and landforms are formed as a result of interaction with water (such as clay and sedimentary rocks ) or as a byproduct of life (such as limestone or coal), interaction with the atmosphere, volcanically or artificially. A true Earth analog therefore might need to have formed through similar processes, having possessed an atmosphere, volcanic interactions with
3658-448: The three planets of Kepler-42 (all discovered in 2011) are very hot, and Mars , Ganymede and Titan are frigid worlds, resulting also in wide variety of surface and atmospheric conditions. The masses of the Solar System's moons are a tiny fraction of that of Earth whereas the masses of extrasolar planets are very difficult to accurately measure. However discoveries of Earth-sized terrestrial planets are important as they may indicate
3720-448: The unending heat and light from a pair of suns, and Mark Hodder 's 2012 novel A 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. Hal Clement's 1957 novel Cycle of Fire depicts a planet in a binary star system where the seasons last for decades and different species dominate the hot and cold parts of the year, Poul Anderson 's 1974 novel Fire Time portrays
3782-408: Was once again perceived to be more Earth-like. Likewise, until the 1960s, Venus was believed by many, including some scientists, to be a warmer version of Earth with a thick atmosphere and either hot and dusty or humid with water clouds and oceans. Venus in fiction was often portrayed as having similarities to Earth and many speculated about Venusian civilization. These beliefs were dispelled in
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#17327913938553844-417: Was thought by many, including some scientists, to be very similar to Earth, only drier with a thick atmosphere, similar axial tilt, orbit and seasons as well as a Martian civilization that had built great Martian canals . These theories were advanced by Giovanni Schiaparelli , Percival Lowell and others. As such Mars in fiction portrayed the red planet as similar to Earth's deserts. Images and data from
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