Hypothetical Bodies, Hypothetical Objects, Hypothetical Regions and Hypotheses

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This article provides a comprehensive list of all hypothetical bodies, hypothetical objects, hypothetical regions, and hypotheses. It serves as a detailed catalog for exploring theoretical concepts, proposed entities, and speculative ideas that have been postulated in various scientific, philosophical, and imaginative contexts. Each category is designed to encompass a broad spectrum of possibilities, from astronomical bodies and unidentified celestial phenomena to speculative geographic areas and conceptual frameworks.

Hypothetical planets

Main Article: List of hypothetical planets

Hypothetical planets are celestial bodies that are theorized to exist based on scientific predictions, simulations, or observations of gravitational effects but have not yet been directly observed or confirmed. These planets often arise in discussions of anomalies in planetary systems or unexplained phenomena, such as the potential existence of Planet Nine, which is hypothesized to orbit the Sun far beyond Neptune. Hypothetical planets also appear in speculative scenarios, such as those exploring alternative solar system formations or fictional universes.

Enyo and Bellona

Artist depiction of Enyo and Bellona

Main Article: Enyo and Bellona (hypothetical planets)

Enyo and Bellona (originally A and B respectively) were two massive super-Earth or supergiant planets theorized by Michael Woolfson as part of his Capture theory on the formation of the Solar System. According to this hypothesis, these two planets were the original innermost members of the Solar System but experienced a catastrophic collision shortly after their formation. In the initial version of the theory, the collision led to the ejection of A/Enyo, along with its moons—including Mars, the Moon, Pluto, and other dwarf planets—out of the Solar System, while the fragments of B/Bellona coalesced to form the Earth, Venus, Mercury, the asteroid belt, and comets. However, an updated version of the hypothesis portrays Enyo and Bellona as even more massive than Jupiter. Their collision resulted in an explosive event so energetic that it triggered deuterium fusion within their interiors, effectively turning them into temporary stars. This violent explosion dispersed their outer layers, leaving behind their dense cores, which subsequently evolved into Venus and Earth.

Vulcan

Artist depiction of Vulcan

Main Article: Vulcan (hypothetical planet)

Vulcan is a small hypothetical planet that was proposed to exist in an orbit between Mercury and the Sun. Its existence was first hypothesized in the 19th century by French mathematician Urbain Le Verrier, who sought to explain peculiarities in Mercury's orbit that could not be accounted for by Newtonian mechanics. Le Verrier attributed these anomalies to the gravitational influence of an unseen planet, which he named "Vulcan," drawing inspiration from a supposed observation of the planet’s transit reported by physician Lescarbault. This claim sparked significant interest and led to widespread efforts to confirm Vulcan's existence. Over time, Vulcan also attracted attention as a possible explanation for the lack of observed mass between Mercury's orbit and the Sun. However, despite extensive searches, no such planet was ever discovered. Ultimately, the so-called “anomalies” in Mercury’s orbit were resolved by Albert Einstein’s theory of general relativity in the early 20th century, which demonstrated that Mercury’s orbit was distorted by the curvature of spacetime near the Sun. Although the idea of Vulcan was effectively dismissed, the concept of small celestial objects within Mercury's orbit persisted. These hypothetical bodies, now known as Vulcanoids, remain a subject of scientific interest, as they could theoretically exist in stable orbits close to the Sun.

Counter-Earth

Artist depiction of Counter-Earth

Main Article: Counter-Earth

Counter-Earth, also known as Antichthon, is a hypothetical celestial body proposed by the pre-Socratic Greek philosopher Philolaus (c. 470–c. 385 BC) as part of his non-geocentric cosmological model. In this system, Philolaus rejected the traditional geocentric view of the universe, instead suggesting that all celestial bodies, including the Earth, revolve around an unseen "Central Fire." This Central Fire was distinct from the Sun, which itself was believed to orbit this central point along with other celestial bodies. Counter-Earth was posited to exist in the same orbital path as Earth but on the opposite side of the Central Fire, rendering it permanently hidden from view. Philolaus's concept of Counter-Earth served as a philosophical tool to explain certain astronomical phenomena and maintain symmetry in his model of the cosmos, though it lacked observational evidence. And modern astronomy has long since discredited the idea of a Counter-Earth.

Nibiru

Artist depiction of Nibiru

Main Article: Nibiru (hypothetical planet)

Nibiru, or Planet X, is a hypothetical planet speculated to exist within the Solar System and often associated with apocalyptic scenarios, particularly the so-called "Nibiru cataclysm," which describes a disastrous collision or near-miss between Earth and a massive celestial object. This idea first gained attention in 1995 when Nancy Lieder, founder of the website ZetaTalk, claimed to have received warnings from extraterrestrials of the Zeta Reticuli star system, predicting that Nibiru would pass through the inner Solar System in May 2003 and cause a catastrophic pole shift. When this failed to occur, the date was postponed, and the theory gained traction among Internet doomsday groups, later becoming entwined with the 2012 phenomenon. Predictions, including one by "Christian numerologist" David Meade for September 23, 2017, have repeatedly failed, and astronomers consistently reject the concept as pseudoscience, emphasizing that such an object would have caused detectable gravitational disruptions. The name "Nibiru" originates from the interpretations of ancient astronaut writer Zecharia Sitchin, who linked it to Babylonian and Sumerian mythology but denied connections to doomsday claims.

Theia

Artist depiction of Theia

Main Article: Theia (hypothetical planet)

Theia is a hypothesized ancient planetary-mass object that played a critical role in shaping the early Solar System, particularly in the formation of the Moon. According to the Giant-impact hypothesis, Theia collided with the early Earth approximately 4.5 billion years ago in a cataclysmic event that reshaped both bodies. Theia is thought to have been an Earth trojan, sharing Earth’s orbit, and was roughly the size of Mars, with a diameter of about 6,102 kilometers (3,792 miles). Geologist Edward Young of the University of California, Los Angeles, analyzing isotopic evidence from lunar rocks collected during Apollo missions 12, 15, and 17, proposed that the collision was a head-on impact rather than the previously suggested glancing blow. This direct collision would have caused Theia to be almost entirely absorbed into Earth’s mantle, while the immense energy released during the impact ejected vast amounts of debris into orbit. Over time, this debris coalesced under gravity to form the Moon. The hypothesis also explains the Moon’s composition, which is similar to Earth’s mantle, suggesting a shared origin.

Phaeton

Artist depiction of Pheaton

Main Article: Phaeton (hypothetical planet)

Phaeton (or Phaëton, less commonly Phaethon) is a hypothetical planet once theorized to have existed between the orbits of Mars and Jupiter, whose destruction was believed to have resulted in the formation of the asteroid belt. The name "Phaeton" originates from Greek mythology, referencing the son of the sun god Helios who, in a reckless attempt to drive his father’s solar chariot, caused chaos and was ultimately struck down by Zeus to prevent further calamity. This mythological imagery inspired the idea of a lost planet whose fate mirrored Phaethon’s destruction. The hypothesis gained some popularity as a way to explain the presence of countless fragments in the asteroid belt, suggesting they were remnants of a larger planetary body that was shattered by a collision or gravitational disruption. However, this theory was later ruled out as scientific understanding advanced, with studies showing that the asteroid belt consists of primordial material that never coalesced into a planet due to the strong gravitational influence of nearby Jupiter. This dynamic prevented the accretion of planet-sized bodies, leaving behind the belt of rocky debris we observe today.

Planet V

Artist depiction of Planet V

Main Article: Planet V

Planet V is a hypothetical fifth terrestrial planet proposed by NASA scientists John Chambers and Jack J. Lissauer as part of the Planet V hypothesis. According to this theory, Planet V once existed between Mars and the asteroid belt but was destabilized during the early Solar System's chaotic evolution. The hypothesis suggests that gravitational perturbations from the other terrestrial planets caused Planet V’s orbit to shift, eventually crossing into the asteroid belt. This orbital disruption is thought to have triggered a cascade of collisions, dislodging asteroids and sending them hurtling toward the inner Solar System, thereby contributing to the Late Heavy Bombardment during the Hadean Era, a period marked by intense impacts on Earth, the Moon, and other planets. The initial findings supporting this idea were presented by Chambers and Lissauer at the 33rd Lunar and Planetary Science Conference, held from March 11 to 15, 2002.

Krypton

Artist depiction of Krypton

Main Article: Krypton (hypothetical planet)

Krypton is a hypothetical gas giant proposed by Michael Ovenden, who theorized that a planet of this size once existed between Mars and the asteroid belt. Speculated to have been as large as Saturn, Krypton was suggested to have played a role in the formation of the asteroid belt, potentially contributing fragments of its own structure after a catastrophic event. This idea aligns with earlier hypotheses, such as those concerning Planet V and Phaeton, which also proposed planets in this region of the Solar System. However, like its counterparts, Krypton has been ruled out as a plausible explanation for the asteroid belt. Current scientific consensus holds that the asteroid belt consists of primordial material from the protoplanetary disk that never coalesced into a planet due to Jupiter's strong gravitational influence. During the early Solar System’s formation, Jupiter’s gravitational perturbations disrupted the process of accretion, preventing the small protoplanets in this region from merging into a larger planetary body. While the name "Krypton" evokes the fictional destroyed homeworld of Superman.

Fifth Giant

Artist depiction of the Fifth Giant

Main Article: Fifth Giant

The Fifth Giant is a hypothetical planet proposed by the Five-planet Nice model and the Jumping-Jupiter scenario, theorized to have existed between Saturn and Uranus during the early stages of the Solar System’s formation. According to these models, the Fifth Giant was likely an ice giant, similar in composition and size to Uranus and Neptune, and played a significant role in the evolution of the outer planets. As Neptune migrated outward due to gravitational interactions with the surrounding protoplanetary disk, the Fifth Giant’s orbit became increasingly unstable. Eventually, interactions with Saturn and Jupiter amplified these instabilities, leading to the ejection of the Fifth Giant from the Solar System entirely. This event would have contributed to the rearrangement of the outer planets and may have influenced the scattering of smaller bodies, such as comets and asteroids, throughout the Solar System. Some researchers have drawn connections between the Fifth Giant and Planet Nine, another hypothetical ice giant thought to exist in a distant orbit or to have been ejected during the same migratory period. If the Fifth Giant and Planet Nine are related, its remnants could still exist in the outer reaches of the Solar System or even as a rogue planet drifting through interstellar space.

Uranus Impactor

Artist depiction of the Uranus Impactor

Main Article: Uranus Impactor

The Uranus Impactor is a hypothetical planetary body theorized to have collided with Uranus approximately 3 to 4 billion years ago, fundamentally altering the planet’s orientation and contributing to its unique characteristics. This collision is believed to have caused Uranus’s extreme axial tilt of 98°, where the planet essentially rotates on its side relative to the plane of the Solar System. The impact may have also played a critical role in the formation of Uranus’s rings and natural satellites, as debris from the collision likely coalesced under gravitational forces. The Uranus Impactor is estimated to have been roughly twice the size of Earth, classifying it as a "Super-Earth"—a type of planet with a mass greater than Earth’s but smaller than that of the ice giants like Uranus and Neptune.

Triton's Binary Partner

Artist depiction of Triton's Binary Partner

Main Article: Triton’s Binary Partner

Triton's Binary Partner is a hypothetical celestial body proposed as a potential explanation for Triton’s retrograde orbit and its capture by Neptune. According to this theory, Triton was once part of a binary system with another Kuiper Belt Object (KBO) around 4 billion years ago. During a close encounter with Neptune, gravitational interactions likely disrupted the binary system, causing Triton to be captured by Neptune’s gravity while its binary partner was ejected into space. The properties of this hypothetical companion remain uncertain, but it is speculated to have been similar to Triton in composition, albeit smaller and less massive. This scenario aligns with models of gravitational dynamics, as the interaction between Neptune and a binary system provides a plausible mechanism for Triton’s capture into its unusual retrograde orbit. If Triton’s binary partner still exists, it could potentially be a distant, unobserved KBO or a lost wanderer in interstellar space.

Haumea Impactor

Main Article: Haumea Impactor

The Haumea Impactor is a hypothetical object that collided with the dwarf planet Haumea, potentially influencing its shape and characteristics. Haumea is an elongated, ellipsoid-shaped body located in the Kuiper belt, and its unusual shape has long been a subject of scientific interest. One theory suggests that Haumea's current form could be the result of a high-speed collision with another object early in its history, which may have caused it to spin rapidly and flatten at the poles. The Haumea Impactor would likely have been a large, icy body, and its collision with Haumea could have created it's unique characteristics, including its fast rotation and the presence of its ring system.

Quaoar Impactor

Main Article: Quaoar Impactor

The Quaoar Impactor is a hypothetical object theorized to have collided with the dwarf planet Quaoar billions of years ago, leading to the formation of its moon, Weywot. This impact event is believed to have been a significant collision, with the Impactor striking Quaoar with enough force to eject material into space. Over time, the ejected debris coalesced under gravitational forces to form Weywot, which now orbits Quaoar. While the exact characteristics of the Quaoar Impactor remain unknown, it is likely to have been a relatively large Kuiper Belt Object (KBO) of comparable size to smaller moons or asteroids.

Brahma

Artist depiction of Brahma

Main Article: Brahma

Brahma is a hypothetical planet once theorized to exist beyond Neptune’s orbit, often mentioned alongside another proposed planet, Vishnu. These planets were speculated to be part of the outer Solar System, possibly influencing the orbits of distant objects or contributing to the gravitational dynamics of the Kuiper Belt. However, the existence of Brahma and Vishnu has never been confirmed, and current evidence suggests they most likely do not exist. Advances in observational technology and astronomical surveys have failed to detect any such planets, leading scientists to attribute the observed anomalies in the outer Solar System to other factors, such as interactions with smaller Kuiper Belt Objects or distant influences like Planet Nine, another hypothetical planet.

Vishnu

Artist depiction of Vishnu

Main Article: Vishnu

Vishnu is one of two hypothetical planets proposed by Venkatesh P. Ketakar, who theorized that these planets existed beyond Neptune’s orbit, with the other being named Brahma. Ketakar suggested their presence based on calculations and interpretations of celestial mechanics, aiming to explain certain observed phenomena in the outer Solar System. However, no direct evidence for Vishnu has ever been found, and modern astronomical surveys have not detected any planets matching its proposed characteristics. As a result, Vishnu is now widely regarded as a speculative idea rather than a real celestial body.

Oceanus

Main Article: Oceanus

Oceanus was a hypothetical planet proposed by astronomer Thomas J.J. See as part of a trio of planets theorized to exist beyond Neptune. According to See’s speculation, Oceanus was one of these distant worlds, accompanied by two other unnamed planets referred to as the "Trans-Oceanus Planets". These planets were proposed as an attempt to explain certain anomalies in the orbits of known outer Solar System bodies. However, no evidence for Oceanus or its companions has ever been found, and advancements in astronomical observations have rendered their existence highly unlikely.

Hades

Artist depiction of Hades

Main Article: Hades

Hades was a hypothetical planet proposed by Theodor Grigull, who suggested its existence to account for the perturbations observed in the orbits of many comets. Grigull theorized that Hades resided beyond Neptune’s orbit, acting as a gravitational influence on these distant objects. Despite the intriguing nature of this idea, no evidence for Hades has ever been found, and extensive surveys of the outer Solar System have failed to detect any such planet. Modern explanations for the behavior of comets and other distant bodies often involve interactions with known planets, the collective influence of smaller Kuiper Belt Objects, or even the theoretical Planet Nine, which remains under investigation.

Planet Nine

Artist depiction of Planet Nine

Main Article: Planet Nine

Planet Nine is a hypothetical planet theorized to exist in the outermost reaches of the Solar System, possibly extending into the Oort Cloud. Based on indirect evidence, it is estimated to be about 40,000 kilometers in diameter—potentially larger than Earth but smaller than Neptune—placing it in the category of a Super-Earth or a sub-Neptune. Its composition is speculated to be similar to that of the ice giants, consisting primarily of hydrogen, helium, methane, water, and ammonia. Planet Nine may also feature a simple ring system akin to Neptune’s. Due to its vast distance from the Sun, it is hypothesized that a single orbit, or "year," on Planet Nine could take approximately 20,000 Earth years. The planet’s existence has been proposed to explain the unusual clustering of orbits among distant trans-Neptunian objects, which some scientists attribute to the gravitational influence of a massive, unseen object.

Planet Ten

Artist depiction of Planet Ten

Main Article: Planet Ten

Planet Ten is a hypothetical celestial body theorized to exist beyond Neptune and the dwarf planet Pluto, lying near the edge of the Kuiper Belt. Proposed as either a Mars-sized or Earth-sized planet, Planet Ten has not yet been confirmed but remains a subject of speculation in planetary science. One of the key reasons for its hypothesized existence is its potential role in explaining the "Kuiper Cliff," a region approximately 50 astronomical units (AU) from the Sun where the density of Kuiper Belt Objects sharply decreases. This abrupt cutoff has led some to suggest that an unknown planetary body might be gravitationally influencing the region, effectively "clearing" material from the area. Like Planet Nine, Planet Ten remains undetected, and its existence is based on indirect evidence. Interestingly, due to its proposed position closer to the Sun than Planet Nine, some researchers suggest it could alternatively be referred to as Planet Nine.

Planet X

Main Article: Planets beyond Neptune

Planet X, proposed in 1906 by American astronomer Percival Lowell, was hypothesized to be a large, unknown planet beyond Neptune that could explain the unusual orbits of Uranus and Neptune. Lowell believed that the gravitational effects of this unseen planet were causing the irregularities in their orbits, suggesting that Planet X's mass was influencing the outer reaches of the solar system. His theory, though groundbreaking at the time, remained speculative due to a lack of direct observational evidence. Lowell's search for Planet X led to the discovery of Pluto in 1930, but Pluto's small size and mass were insufficient to account for the orbital anomalies that had initially prompted the search for a larger planet. As a result, the idea of Planet X evolved over time, eventually contributing to the development of modern theories of Trans-Neptunian objects and the Kuiper belt.

Pickering's Planets

Main Article: Pickering's Planets

Pickering's Planets refer to a series of hypothetical planets proposed by astronomer William Henry Pickering between 1909 and 1938. Over the course of his work, Pickering suggested the existence of seven to eleven planets beyond Neptune, based on perceived irregularities in the orbits of known celestial bodies. These proposed planets were theorized to explain gravitational perturbations observed in the outer Solar System, though their existence was never confirmed. Advances in astronomical techniques and a better understanding of orbital mechanics have since ruled out these planets, with many of the irregularities Pickering sought to explain later attributed to observational errors or alternative phenomena.

Tyche

Artist depiction of Tyche

Main Article: Tyche (hypothetical planet)

Tyche was a hypothesized giant planet proposed to exist in the distant outer reaches of the Oort Cloud, far beyond the orbit of Neptune and Pluto. If it were discovered, it was speculated to be the largest planet in the Solar System, with a mass approximately four times that of Jupiter. Tyche was suggested as a potential explanation for certain patterns in the trajectories of comets, which it might have perturbed as they originated from the Oort Cloud. Data from the WISE (Wide-field Infrared Survey Explorer) space telescope, which surveyed the entire sky in infrared wavelengths, was examined for evidence of Tyche and compiled for analysis by March 2012. However, no definitive signs of such a planet were found. While the concept of Tyche remains intriguing, the lack of observational evidence has led most scientists to conclude that it likely does not exist.

Hypothetical Moons

Main Article: Hypothetical Moons

Hypothetical Moons are natural satellites proposed to exist around planets or other celestial bodies but have not yet been confirmed through observation. Some of these moons have been suggested based on indirect evidence, such as gravitational anomalies or unexplained phenomena, while others stem from theoretical models of planetary formation. However, many hypothetical moons have been disproven with advancements in astronomical observation and analysis, revealing that the phenomena they were meant to explain had alternative explanations.

Hermes and Caduceus

Main Article: Hermes and Caduceus

31 Crateris, the star it was mistaken for.

Hermes

Hermes is the nickname given to a hypothetical natural satellite once thought to orbit Mercury. In the early 1970s, observations briefly suggested the existence of such a moon, but this was later disproven when the data was found to be a misinterpretation caused by the star 31 Crateris. Observing a moon around Mercury from Earth is particularly challenging due to Mercury's proximity to the Sun, which creates observational difficulties. For instance, Mercury itself was not observed in the infrared spectrum until 1995. Further investigation by NASA's MESSENGER spacecraft, which conducted an extensive survey of Mercury during its mission from 2011 to 2015, confirmed that no moons orbit the planet.

Fake Image of Caduceus

Caduceus

On April 1, 2012, NASA participated in an April Fools' Day prank by announcing the "discovery" of a new moon orbiting Mercury, named Caduceus. The name referenced to the staff carried by the Roman god Mercury, symbolizing trade and communication. The announcement was intended as a lighthearted joke, as no moons have ever been confirmed around Mercury. Due to its close proximity to the Sun and small size, Mercury is not believed to have the gravitational capacity to retain a natural satellite.

Neith

Spacepedia image of Neith

Main Article: Neith (hypothetical moon)

Neith was a purported natural satellite of Venus, first claimed to have been observed by the astronomer Giovanni Cassini in 1672. Over the next century, several other astronomers also reported sightings of a moon near Venus, lending some credibility to the idea of its existence. However, these observations were inconsistent and could not be reliably confirmed. The last recorded sighting of Neith occurred in 1768, after which no further evidence was found. Eventually, the idea of Neith was dismissed entirely, with astronomers concluding that the sightings were likely due to optical illusions, bright stars near Venus, or observational errors.

Petit's moon

Main Article: Petit's moon

Petit's Moon was the first known claim of a second natural satellite orbiting Earth, proposed by French astronomer Frédéric Petit in 1846 while working at the Toulouse Observatory. Petit asserted that this hypothetical moon followed an elliptical orbit with a period of 2 hours, 44 minutes. The claim gained some attention, as two other observers, Lebon and Dassier, also reported sightings that seemed to support its existence. However, subsequent investigations and observations failed to find any evidence of such a moon. Over time, the idea of Petit's Moon was dismissed as a result of observational errors or misinterpretations, and Earth's status as having only one natural satellite, the Moon, was reaffirmed.

Waltemath's moons

Main Article: Waltemath's moons

Waltemath's Moons refer to a group of tiny, hypothetical moons claimed to orbit Earth, proposed by Hamburg scientist Georg Waltemath in the late 19th century. Waltemath's search was driven by the hypothesis that anomalies in the Moon's orbit could be explained by the gravitational influence of additional, smaller moons. In 1898, he announced the discovery of a secondary moon, describing its orbit as complex and difficult to observe due to its small size and proximity to the Sun. Waltemath later speculated on the existence of even more such moons. However, no evidence of these objects was ever found, and the claims were dismissed as observational errors or miscalculations. Modern astronomy has thoroughly ruled out the existence of additional moons orbiting Earth.

Bagby's Moons

Main Article: Bagby's Moons

Bagby's Moons refer to a speculative concept proposed by astronomer Charles P. Bagby in the 1970s, suggesting the existence of small moons or captured asteroids within Jupiter's Trojan asteroid clouds, located at the planet's Lagrange points L4 and L5. These regions are gravitationally stable zones where the combined forces of Jupiter and the Sun allow celestial bodies to remain in a relatively fixed position relative to the planet. Bagby hypothesized that small moons or similar objects might be hidden within these clouds, potentially influencing the dynamics of the Trojan population and providing clues about the processes that shaped Jupiter's moon system.

Pallas's hypothetical moons

Asteroid Pallas

Main Article: Pallas's hypothetical moons

Observations and historical data have long fueled speculation about the potential existence of moons orbiting the asteroid Pallas, the second-largest body in the asteroid belt. Over the years, various astronomers have proposed hypotheses based on irregularities in Pallas's motion and unusual features observed during occultation events, suggesting the presence of one or more small satellites. However, subsequent observations have failed to confirm these claims, and the evidence remains inconclusive. Despite advancements in telescope technology and space exploration, no definitive detection of moons around Pallas has been made.

Hebe's hypothetical moons

Asteroid (6) Hebe

Main Article: Hebe's hypothetical moons

In 1977, a possible moon orbiting the asteroid Hebe was suggested based on observations that hinted at irregularities in its brightness and motion. The hypothesis proposed that these anomalies could be explained by the presence of a small satellite in orbit around Hebe. However, subsequent observations have not confirmed the existence of such a moon, and the claim remains unverified.

Metis's hypothetical moon

Main Article: Metis's hypothetical moon

Amphitrite's hypothetical moon

Main Article: Amphitrite's hypothetical moon

Amphitrite's hypothetical moon is a theoretical natural satellite orbiting the asteroid 29 Amphitrite, one of the largest asteroids in the main asteroid belt. Amphitrite, classified as an S-type asteroid, has a diameter of approximately 212 kilometers, and its relatively high brightness and mass make it a candidate for hosting a moon. While no direct observations of a satellite have been confirmed, the possibility has been suggested based on irregularities in Amphitrite's light curve and gravitational interactions observed during occultation events. If such a moon exists, it would likely be a small, irregularly shaped body, potentially formed from debris resulting from a past collision or as a captured object during the early history of the asteroid belt.

Chiron

Main Article: Chiron (hypothetical moon)

Chiron is the name given to a supposed moon of Saturn that was reported by astronomer Hermann Goldschmidt in 1861. Goldschmidt, who discovered several asteroids during his career, claimed to have observed this satellite orbiting Saturn. However, further observations failed to confirm its existence, and it has since been determined that no such moon exists. The claim likely arose from an observational error or misinterpretation of visual data, which was not uncommon given the limitations of 19th-century telescopic technology.

Chrysalis

Artist depiction of Chrysalis

Main Article: Chrysalis (hypothetical moon)

Chrysalis is the name given to a hypothesized moon that is believed to have once orbited Saturn before being destroyed by the planet's tidal forces. According to this theory, Chrysalis played a crucial role in shaping some of Saturn's most distinctive features. Its destruction may have contributed to the formation of Saturn's rings, with debris from the moon being scattered and eventually coalescing into the structures observed today. Additionally, the gravitational interactions between Chrysalis and other moons or Saturn itself might have influenced the unusual axial tilt of the planet.

Themis

Artist depiction of Themis

Main Article: Themis (hypothetical moon)

On April 28, 1905, William H. Pickering, known for his earlier discovery of Saturn's moon Phoebe in 1898, announced the discovery of a tenth satellite of Saturn, which he named Themis. Pickering based his claim on photographic plates taken between April 17 and July 8, 1904, a total of thirteen images in which he believed the moon was visible. Despite his confidence in the discovery, no other astronomer has ever been able to confirm the existence of Themis. Subsequent observations and studies have not provided any evidence of such a moon, leading to the conclusion that Themis does not exist.

Sedna I

Artist depiction of Sedna I

Main Article: (90377) Sedna I (disproven moon)

Sedna I was a hypothesized moon once thought to orbit the trans-Neptunian object Sedna. This idea arose due to Sedna’s unusually slow rotation, which suggested the possibility of tidal interactions with a satellite. However, no definitive evidence of such a moon has ever been found. No specific data regarding its mass, radius, or other physical properties has been determined, and observations have failed to detect any signs of a companion object. It was speculated that if such a moon existed, it might be either very distant, very close to Sedna, or possess a low brightness or albedo, making it difficult to observe.

Varuna I

Artist depiction of Varuna I

Main Article: (20000) Varuna I (hypothetical moon)

Varuna I is a proposed moon of the trans-Neptunian object Varuna, suggested by photometric observations conducted by Estela Fernández-Valenzuela and colleagues in 2019. The hypothesis arose from irregularities in Varuna's light curve, which hinted at the potential presence of a companion object. If Varuna I exists, it is believed to orbit between 1,300 and 2,000 kilometers above Varuna’s surface. However, its proximity and small size would make resolving it with current space-based telescopes impossible, as the angular separation falls below their resolution capabilities. Using a Lomb Periodogram analysis, the rotational period of Varuna I has been estimated at approximately 11 hours, 58 minutes, 54 seconds, and 840 milliseconds. Despite these findings, no direct visual confirmation of Varuna I has been achieved, leaving its existence speculative.

Herschel's Moons

Titania, the largest moon of Uranus

Main Article: Herschel's Moons

Herschel’s Moons refer to four hypothetical moons of Uranus that were reportedly observed by William Herschel after his discovery of Titania and Oberon in 1787. Herschel claimed to have detected these additional moons during subsequent observations of the planet. However, no other astronomers were able to confirm their existence in later studies. When Uranus was revisited with more advanced telescopes and techniques, the supposed four moons Herschel described were not observed. It is now believed that Herschel's sightings were likely observational errors or artifacts caused by the limitations of his equipment at the time.

Hypothetical Stellar Objects

Main Article: Hypothetical Stellar Objects

Hypothetical Stellar Objects are theoretical celestial bodies proposed to account for unexplained phenomena within the Solar System or the broader universe. These objects, similar to hypothetical planets and moons, were often introduced to address anomalies in observed data or gaps in scientific understanding. Over time, many of these proposed stellar bodies have been disproven or rendered unnecessary due to advancements in observational technology, improved models, or the discovery of alternative explanations.

Nemesis

An artist's impression of Nemesis, if it was a red dwarf.

Main Article: Nemesis (hypothetical star)

Nemesis is a hypothetical red dwarf or brown dwarf star, proposed in 1984 to orbit the Sun at a distance of approximately 95,000 AU (1.5 light-years), slightly beyond the Oort Cloud. The idea was introduced to explain a perceived cycle of mass extinctions in Earth's history, which seemed to occur at regular intervals of about 26 million years. Proponents suggested that Nemesis, a dark red star, could be responsible for disturbing the Oort Cloud and sending comets toward Earth, triggering these extinctions. However, in a 2017 paper, astronomers Sarah Sadavoy and Steven Stahler proposed that the Sun might have once been part of a binary system, implying that Nemesis, if it ever existed, would have separated from the Sun over four billion years ago. This would rule out any connection between Nemesis and the more recent cycles of extinction. Further research, including sky surveys conducted by space probes, failed to detect any evidence of such a star. Additionally, a 2011 study analyzing craters on Earth's surface concluded that the periodic extinction patterns attributed to Nemesis were more likely statistical artifacts rather than evidence of a real astronomical object, leading to the hypothesis being largely dismissed.

Coatlicue

An artist's impression of Coatlicue, if it were an O-Type star.

Main Article: Coatlicue (star)

Coatlicue is a hypothetical star proposed as a potential explanation for the formation of the Sun and other stars. According to this theory, Coatlicue was believed to be a massive, primordial star that played a key role in the processes leading to the formation of the solar system. It was thought that the collapse of a molecular cloud, possibly influenced by the gravitational pull of Coatlicue, could have triggered the formation of the Sun and the surrounding planets. However, this hypothesis remains speculative and lacks substantial observational evidence. As a result, the idea of Coatlicue has largely been overshadowed by more widely accepted models of star formation, such as the nebular hypothesis, which suggests that stars form from the gravitational collapse of gas and dust within molecular clouds, without the need for an external star like Coatlicue.

Hypothetical Regions

Main Article: Other Hypothetical Objects

Hypothetical Solar System Regions refer to theoretical areas within or beyond the known boundaries of the Solar System that are proposed based on scientific speculation, mathematical modeling, or indirect evidence, rather than direct observation. These regions often arise in discussions of unconfirmed celestial phenomena or potential extensions of the Solar System's influence.

Vulcanoid Belt

Artist's impression of a near-vulcanoid asteroid, 2021 PH27.

Main Article: Vulcanoid

The Vulcanoid Belt is a hypothesized population of small, rocky asteroids that may exist in a stable region within Mercury's orbit, approximately 0.08 to 0.21 astronomical units from the Sun. Named after the hypothetical planet Vulcan, once believed to exist in this region, the Vulcanoid Belt is thought to consist of remnants from the early solar system. These objects, if they exist, would be subjected to extreme temperatures and intense solar radiation, making them difficult to detect with current telescopic technology. Despite extensive searches, no Vulcanoids have been conclusively identified, leaving their existence unconfirmed.

Hills cloud

Main Article: Oort cloud

The Hills Cloud, also known as the Inner Oort Cloud, is a theoretical region of icy bodies located beyond the Kuiper Belt and the scattered disk, extending from approximately 2,000 to 20,000 astronomical units (AU) from the Sun. Proposed by astronomer Jack G. Hills, this region is thought to contain a vast population of comets and icy objects that were likely ejected from the inner solar system during its early formation. Unlike the Oort Cloud, which forms a roughly spherical shell, the Hills Cloud is believed to have a more disk-like structure and serves as a reservoir for long-period comets. These objects are less likely to be perturbed by the gravitational influences of passing stars or the galactic tide compared to those in the outer Oort Cloud.

Oort cloud

Main Article: Oort cloud

The Oort Cloud is a vast, spherical region of icy objects that surrounds the outermost edges of the solar system. Extending from about 2,000 to 100,000 astronomical units (AU) from the Sun, it is believed to be the source of long-period comets, which take thousands of years to complete their orbits. The Oort Cloud is composed of remnants from the early solar system, primarily icy bodies made of water, ammonia, and methane. These objects are thought to have been scattered outward by the gravitational influence of the giant planets during the solar system's formation.

Hypotheses and Models

The Solar System's origin and structure have been subjects of various hypotheses and models throughout history, evolving with advancements in astronomy and physics.

Himalia Crash Theory

Main Article: Himalia Crash Theory, Himalia Ring, and Possible Moon

The Himalia Crash Theory suggests that Jupiter’s irregular moon Himalia was once part of a larger celestial body that fragmented due to a high-velocity collision with another object, likely a comet or asteroid. This collision is believed to have generated the faint Himalia Ring, a diffuse ring of debris encircling Jupiter near Himalia's orbit. Observations from the Cassini and New Horizons missions have hinted at this structure, which consists of dust particles gradually spiraling toward Jupiter due to the planet’s strong gravitational and electromagnetic forces. Additionally, remnants of the original collision might include a possible moon or several smaller fragments in similar orbits.

Iapetus' Ring System

Main Article: Iapetus's Ring System

Iapetus, one of Saturn's moons, is unique in the solar system due to its association with a vast, faint ring system. This ring, known as the Iapetus Ring, is thought to be composed of debris from Saturn's outer moon Phoebe. Observations suggest that the material was ejected from Phoebe by impacts and subsequently captured into a diffuse ring orbiting Saturn in a retrograde motion, similar to Phoebe's orbit. The Iapetus Ring lies far from Saturn and is tilted relative to its equatorial plane, with its particles slowly spiraling inward over time. These particles may contribute to the unusual two-tone coloration of Iapetus, where its leading hemisphere is coated with a dark material likely sourced from the ring, while the trailing hemisphere remains bright and reflective.

Nibiru cataclysm

Main Article: Nibiru cataclysm

The Nibiru cataclysm is a supposed global disaster that some conspiracy theorists claim will occur when a large planetary object, often referred to as Nibiru or Planet X, collides with or passes close to Earth. This idea originated from interpretations of ancient Sumerian texts, although no scientific evidence supports the existence of Nibiru or its predicted catastrophic effects. The concept gained widespread attention in the late 20th and early 21st centuries, especially surrounding the year 2012, when some believed the Mayan calendar predicted an apocalypse. But has been debunked by astronomers and scientists.