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149-537: Plutonian may refer to: Plutonian, of or relating to the astronomical object Pluto The Plutonian, a character in Irredeemable A mineral from Pluto (as well as a species) on the TV series " Rick and Morty " See also [ edit ] Plutoid , any trans-Neptunian dwarf planet, for which the name 'plutonian' had originally been proposed Topics referred to by

298-486: A Jupiter -sized (≈318 Earth masses) or larger object out to 26,000 AU. In 2014, based on similarities of the orbits of a group of recently discovered extreme trans-Neptunian objects , astronomers hypothesized the existence of a super-Earth or ice giant planet, 2 to 15 times the mass of the Earth and beyond 200 AU with possibly a highly inclined orbit at some 1,500 AU. In 2016, further work showed this unknown distant planet

447-461: A binary system because the barycenter of their orbits does not lie within either body, and they are tidally locked . New Horizons was the first spacecraft to visit Pluto and its moons, making a flyby on July 14, 2015, and taking detailed measurements and observations. Pluto was discovered in 1930 by Clyde W. Tombaugh , making it by far the first known object in the Kuiper belt. It

596-489: A "dwarf planet" by the current definition, because it would not have cleared its neighbourhood sufficiently. Additionally, speculation of a possible trans-Neptunian planet has revolved around the so-called " Kuiper cliff ". The Kuiper belt terminates suddenly at a distance of 48 AU (7.2 billion km; 4.5 billion mi) from the Sun. Brunini and Melita have speculated that this sudden drop-off may be attributed to

745-534: A 'dwarf' planet" by the IAU." Some members of the public have also rejected the change, citing the disagreement within the scientific community on the issue, or for sentimental reasons, maintaining that they have always known Pluto as a planet and will continue to do so regardless of the IAU decision. In 2006, in its 17th annual words-of-the-year vote, the American Dialect Society voted plutoed as

894-445: A Plutonian diameter greater than 2,360 km, with a "best guess" of 2,368 km. On July 13, 2015, images from NASA's New Horizons mission Long Range Reconnaissance Imager (LORRI), along with data from the other instruments, determined Pluto's diameter to be 2,370 km (1,473 mi), which was later revised to be 2,372 km (1,474 mi) on July 24, and later to 2374 ± 8 km . Using radio occultation data from

1043-522: A brief search for a tenth planet. The search was largely abandoned in the early 1990s, when a study of measurements made by the Voyager 2 spacecraft found that the irregularities observed in Uranus's orbit were due to a slight overestimation of Neptune's mass. After 1992, the discovery of numerous small icy objects with similar or even wider orbits than Pluto led to a debate over whether Pluto should remain

1192-447: A collision could happen. However, Pluto is also protected by its 2:3 orbital resonance with Neptune : for every two orbits that Pluto makes around the Sun, Neptune makes three, in a frame of reference that rotates at the rate that Pluto's perihelion precesses (about 0.97 × 10 degrees per year ). Each cycle lasts about 495 years. (There are many other objects in this same resonance, called plutinos .) At present, in each 495-year cycle,

1341-418: A distant Mars- or Earth-sized planet, currently in a highly eccentric orbit between 100 and 200 AU and orbital period of 1000 years with an inclination of 20° to 40°, was responsible for the structure of the Kuiper belt. They proposed that the perturbations of this planet excited the eccentricities and inclinations of the trans-Neptunian objects , truncated the planetesimal disk at 48 AU, and detached

1490-438: A high albedo , like the giant planets. As a result, it would show a disc with diameter of about one arcsecond and an apparent magnitude between 12 and 13—bright enough to be spotted. Separately, in 1908, Pickering announced that, by analysing irregularities in Uranus's orbit, he had found evidence for a ninth planet. His hypothetical planet, which he termed "Planet O" (because it came after "N", i.e. Neptune), possessed

1639-431: A machine called a blink comparator , which by exchanging images quickly created a time lapse illusion of the movement of any planetary body. To reduce the chances that a faster-moving (and thus closer) object be mistaken for the new planet, Tombaugh imaged each region near its opposition point, 180 degrees from the Sun, where the apparent retrograde motion for objects beyond Earth's orbit is at its strongest. He also took

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1788-495: A major planet such as Jupiter, or it may be one of many long-period planetary objects yet to be discovered, or a bright cometary object." In that same article, Harvard Observatory director Harlow Shapley wrote that Pluto was a "member of the Solar System not comparable with known asteroids and comets, and perhaps of greater importance to cosmogony than would be another major planet beyond Neptune." In 1931, after examining

1937-560: A massive object as Brady's Planet X would have severely affected the orbits of known outer planets. Although its mission did not involve a search for Planet X, the IRAS space observatory made headlines briefly in 1983 due to an "unknown object" that was at first described as "possibly as large as the giant planet Jupiter and possibly so close to Earth that it would be part of this Solar System". Further analysis revealed that of several unidentified objects, nine were distant galaxies and

2086-536: A mean orbital radius of 51.9 AU and an orbital period of 373.5 years. Plates taken at his observatory in Arequipa , Peru, showed no evidence for the predicted planet, and British astronomer P. H. Cowell showed that the irregularities observed in Uranus's orbit virtually disappeared once the planet's displacement of longitude was taken into account. Lowell himself, despite his close association with Pickering, dismissed Planet O out of hand, saying, "This planet

2235-437: A moving object on photographic plates taken on 23 January and 29 January of that year. A lesser-quality photograph taken on January 21 confirmed the movement. Upon confirmation, Tombaugh walked into Slipher's office and declared, "Doctor Slipher, I have found your Planet X." The object was just six degrees from one of two locations for Planet X Lowell had suggested; thus it seemed he had at last been vindicated. After

2384-428: A near-2:1 resonance, are not in full resonance. His calculations predicted a mean distance for Brahma of 38.95 AU and an orbital period of 242.28 Earth years (3:4 resonance with Neptune). When Pluto was discovered 19 years later, its mean distance of 39.48 AU and orbital period of 248 Earth years were close to Ketakar's prediction (Pluto in fact has a 2:3 resonance with Neptune ). Ketakar made no predictions for

2533-419: A number of astronomers kept up the search for Lowell's Planet X, convinced that, because Pluto was no longer a viable candidate, an unseen tenth planet must have been perturbing the outer planets. In the 1980s and 1990s, Robert Harrington led a search to determine the real cause of the apparent irregularities. He calculated that any Planet X would be at roughly three times the distance of Neptune from

2682-408: A number of objects in a similar region, whose various orbital configurations would provide an indication as to their history. If Sedna had been pulled into its orbit by a trans-Neptunian planet, any other objects found in its region would have a similar perihelion to Sedna (around 80 AU (12 billion km; 7.4 billion mi)). In 2008, Tadashi Mukai and Patryk Sofia Lykawka suggested

2831-547: A planet, or whether it and its neighbours should, like the asteroids , be given their own separate classification. Although a number of the larger members of this group were initially described as planets, in 2006 the International Astronomical Union (IAU) reclassified Pluto and its largest neighbours as dwarf planets , leaving Neptune the farthest known planet in the Solar System . While

2980-427: A planet. Entitled "The Great Planet Debate", the conference published a post-conference press release indicating that scientists could not come to a consensus about the definition of planet. In June 2008, the IAU had announced in a press release that the term " plutoid " would henceforth be used to refer to Pluto and other planetary-mass objects that have an orbital semi-major axis greater than that of Neptune, though

3129-498: A planet. Barely a month after its discovery was announced, on April 14, 1930, in an article in The New York Times , Armin O. Leuschner suggested that Pluto's dimness and high orbital eccentricity made it more similar to an asteroid or comet: "The Lowell result confirms the possible high eccentricity announced by us on April 5. Among the possibilities are a large asteroid greatly disturbed in its orbit by close approach to

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3278-401: A possible Mars-sized planet, possibly up to 2.4  M E , residing at the edge of the Solar System, which many news sources began referring to as "Planet Ten". Shortly after it was proposed, Lorenzo Iorio showed that the hypothetical planet's existence cannot be ruled out by Cassini ranging data. Starting in 2018, several surveys have discovered multiple objects located beyond

3427-525: A resolution in honor of Clyde Tombaugh, the discoverer of Pluto and a longtime resident of that state, that declared that Pluto will always be considered a planet while in New Mexican skies and that March 13, 2007, was Pluto Planet Day. The Illinois Senate passed a similar resolution in 2009 on the basis that Tombaugh was born in Illinois. The resolution asserted that Pluto was "unfairly downgraded to

3576-465: A role in the creation of the superresonance. The 2nd-largest known plutino , Orcus , has a diameter around 900 km and is in a very similar orbit to that of Pluto. However, the orbits of Pluto and Orcus are out of phase, so that the two never approach each other. It has been termed the "anti-Pluto", and is named for the Etruscan counterpart to the god Pluto . Pluto's rotation period , its day,

3725-447: A sample of his astronomical drawings. Tombaugh's task was to systematically image the night sky in pairs of photographs, then examine each pair and determine whether any objects had shifted position. Using a blink comparator , he rapidly shifted back and forth between views of each of the plates to create the illusion of movement of any objects that had changed position or appearance between photographs. On February 18, 1930, after nearly

3874-598: A small increase in Pluto's surface temperature can lead to exponential increases in Pluto's atmospheric density; from 18 hPa to as much as 280 hPa (three times that of Mars to a quarter that of the Earth). At such densities, nitrogen could flow across the surface as liquid. Just like sweat cools the body as it evaporates from the skin, the sublimation of Pluto's atmosphere cools its surface. Pluto has no or almost no troposphere ; observations by New Horizons suggest only

4023-475: A small margin, but is less massive than Eris . Like other Kuiper belt objects, Pluto is made primarily of ice and rock and is much smaller than the inner planets . Pluto has roughly one-sixth the mass of the Moon , and one-third its volume. Pluto has a moderately eccentric and inclined orbit, ranging from 30 to 49 astronomical units (4.5 to 7.3  billion kilometres ; 2.8 to 4.6 billion miles ) from

4172-532: A small region of Pluto's orbit lies closer to the Sun than Neptune's. The Pluto–Charon barycenter came to perihelion on September 5, 1989, and was last closer to the Sun than Neptune between February 7, 1979, and February 11, 1999. Although the 3:2 resonance with Neptune (see below) is maintained, Pluto's inclination and eccentricity behave in a chaotic manner. Computer simulations can be used to predict its position for several million years (both forward and backward in time), but after intervals much longer than

4321-492: A swarm of icy bodies left over from the Solar System's formation that orbit near the ecliptic plane just beyond Neptune. Though none were as large as Pluto, some of these distant trans-Neptunian objects, such as Sedna , were initially described in the media as "new planets". In 2005, astronomer Mike Brown and his team announced the discovery of 2003 UB 313 (later named Eris after the Greek goddess of discord and strife),

4470-497: A team of researchers proposed that the mountains Wright Mons and Piccard Mons are actually a merger of many smaller cryovolcanic domes, suggesting a source of heat on the body at levels previously thought not possible. Pluto's diameter is 2 376 .6 ± 3.2 km and its mass is (1.303 ± 0.003) × 10  kg , 17.7% that of the Moon (0.22% that of Earth). Its surface area is 1.774 443 × 10  km , or just slightly bigger than Russia or Antarctica (particularly including

4619-513: A thin tropospheric boundary layer . Its thickness in the place of measurement was 4 km, and the temperature was 37±3 K. The layer is not continuous. In July 2019, an occultation by Pluto showed that its atmospheric pressure, against expectations, had fallen by 20% since 2016. In 2021, astronomers at the Southwest Research Institute confirmed the result using data from an occultation in 2018, which showed that light

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4768-406: A third image as a control to eliminate any false results caused by defects in an individual plate. Tombaugh decided to image the entire zodiac, rather than focus on those regions suggested by Lowell. By the beginning of 1930, Tombaugh's search had reached the constellation of Gemini. On 18 February 1930, after searching for nearly a year and examining nearly 2 million stars, Tombaugh discovered

4917-411: A trans-Neptunian object then thought to be just barely larger than Pluto. Soon afterwards, a NASA Jet Propulsion Laboratory press release described the object as the "tenth planet". Eris was never officially classified as a planet, and the 2006 definition of planet defined both Eris and Pluto not as planets but as dwarf planets because they have not cleared their neighbourhoods . They do not orbit

5066-513: A trans-Neptunian planet, which he named Planet X , a name previously used by Gabriel Dallet. The X in the name represents an unknown and is pronounced as the letter, as opposed to the Roman numeral for 10 (at the time, Planet X would have been the ninth planet). Lowell's hope in tracking down Planet X was to establish his scientific credibility, which had eluded him due to his widely derided belief that channel-like features visible on

5215-592: A year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and 29. A lesser-quality photograph taken on January 21 helped confirm the movement. After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. One Plutonian year corresponds to 247.94 Earth years; thus, in 2178, Pluto will complete its first orbit since its discovery. The name Pluto came from

5364-513: Is different from Wikidata All article disambiguation pages All disambiguation pages Pluto Pluto ( minor-planet designation : 134340 Pluto ) is a dwarf planet in the Kuiper belt , a ring of bodies beyond the orbit of Neptune . It is the ninth-largest and tenth-most- massive known object to directly orbit the Sun . It is the largest known trans-Neptunian object by volume, by

5513-429: Is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of water ice. The pre– New Horizons estimate for the diameter of the core is 1700 km , 70% of Pluto's diameter. It is possible that such heating continues, creating a subsurface ocean of liquid water 100 to 180 km thick at the core–mantle boundary. In September 2016, scientists at Brown University simulated

5662-405: Is divided into roughly 20 regularly spaced haze layers up to 150 km high, thought to be the result of pressure waves created by airflow across Pluto's mountains. Pluto has five known natural satellites . The largest and closest to Pluto is Charon . First identified in 1978 by astronomer James Christy , Charon is the only moon of Pluto that may be in hydrostatic equilibrium . Charon's mass

5811-501: Is equal to 6.387 Earth days. Like Uranus and 2 Pallas , Pluto rotates on its "side" in its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme; at its solstices , one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness. The reason for this unusual orientation has been debated. Research from the University of Arizona has suggested that it may be due to

5960-414: Is highly compact: the five known satellites orbit within the inner 3% of the region where prograde orbits would be stable. The orbital periods of all Pluto's moons are linked in a system of orbital resonances and near-resonances . When precession is accounted for, the orbital periods of Styx, Nix, and Hydra are in an exact 18:22:33 ratio. There is a sequence of approximate ratios, 3:4:5:6, between

6109-406: Is highly reflective. This meant that Pluto, far from being dark, was in fact exceptionally bright, and thus was probably no more than 1 ⁄ 100  Earth mass. Pluto's size was finally determined conclusively in 1978, when American astronomer James W. Christy discovered its moon Charon . This enabled him, together with Robert Sutton Harrington of the U.S. Naval Observatory, to measure

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6258-426: Is less massive than the dwarf planet Eris , a trans-Neptunian object discovered in 2005, though Pluto has a larger diameter of 2,376.6 km compared to Eris's approximate diameter of 2,326 km. With less than 0.2 lunar masses, Pluto is much less massive than the terrestrial planets , and also less massive than seven moons : Ganymede , Titan , Callisto , Io , the Moon , Europa , and Triton . The mass

6407-527: Is less than 10 million years old. Latest studies have shown that the surface has an age of 180 000 +90 000 −40 000 years. The New Horizons science team summarized initial findings as "Pluto displays a surprisingly wide variety of geological landforms, including those resulting from glaciological and surface–atmosphere interactions as well as impact, tectonic , possible cryovolcanic , and mass-wasting processes." In Western parts of Sputnik Planitia there are fields of transverse dunes formed by

6556-579: Is likely to be on an inclined, eccentric orbit that goes no closer than about 200 AU and no farther than about 1,200 AU from the Sun. The orbit is predicted to be anti-aligned to the clustered extreme trans-Neptunian objects. Because Pluto is no longer considered a planet by the IAU, this new hypothetical object has become known as Planet Nine . In the 1840s, the French mathematician Urbain Le Verrier used Newtonian mechanics to analyse perturbations in

6705-410: Is more similar to that of Io with slightly more orange and significantly less red than Mars . Notable geographical features include Tombaugh Regio, or the "Heart" (a large bright area on the side opposite Charon), Belton Regio , or the "Whale" (a large dark area on the trailing hemisphere), and the " Brass Knuckles " (a series of equatorial dark areas on the leading hemisphere). Sputnik Planitia,

6854-735: Is much less than thought before Charon was discovered. The discovery of Pluto's satellite Charon in 1978 enabled a determination of the mass of the Pluto–Charon system by application of Newton's formulation of Kepler's third law . Observations of Pluto in occultation with Charon allowed scientists to establish Pluto's diameter more accurately, whereas the invention of adaptive optics allowed them to determine its shape more accurately. Determinations of Pluto's size have been complicated by its atmosphere and hydrocarbon haze. In March 2014, Lellouch, de Bergh et al. published findings regarding methane mixing ratios in Pluto's atmosphere consistent with

7003-552: Is sufficient to cause the barycenter of the Pluto–Charon system to be outside Pluto. Beyond Charon there are four much smaller circumbinary moons. In order of distance from Pluto they are Styx, Nix, Kerberos, and Hydra. Nix and Hydra were both discovered in 2005, Kerberos was discovered in 2011, and Styx was discovered in 2012. The satellites' orbits are circular (eccentricity < 0.006) and coplanar with Pluto's equator (inclination < 1°), and therefore tilted approximately 120° relative to Pluto's orbit. The Plutonian system

7152-538: Is sufficiently delayed that at the second perihelion of each cycle it will not be far ahead of Neptune coming behind it, and Neptune will start to decrease Pluto's period again. The whole cycle takes about 20,000 years to complete. Numerical studies have shown that over millions of years, the general nature of the alignment between the orbits of Pluto and Neptune does not change. There are several other resonances and interactions that enhance Pluto's stability. These arise principally from two additional mechanisms (besides

7301-475: Is therefore moving faster, so during the first of two orbits in the 495-year cycle, it is approaching Neptune from behind. At present it remains between 50° and 65° behind Neptune for 100 years (e.g. 1937–2036). The gravitational pull between the two causes angular momentum to be transferred to Pluto. This situation moves Pluto into a slightly larger orbit, where it has a slightly longer period, according to Kepler's third law . After several such repetitions, Pluto

7450-581: Is very properly designated "O", [for it] is nothing at all." Unbeknownst to Pickering, four of the photographic plates taken in the search for "Planet O" by astronomers at the Mount Wilson Observatory in 1919 captured images of Pluto , though this was only recognised years later. Pickering went on to suggest many other possible trans-Neptunian planets up to the year 1932, which he named P , Q , R , S , T , and U ; none were ever detected. Lowell's sudden death in 1916 temporarily halted

7599-527: The Antarctic sea ice during winter). Its surface gravity is 0.063 g (compared to 1 g for Earth and 0.17 g for the Moon). This gives Pluto an escape velocity of 4,363.2 km per hour / 2,711.167 miles per hour (as compared to Earth's 40,270 km per hour / 25,020 miles per hour). Pluto is more than twice the diameter and a dozen times the mass of Ceres , the largest object in the asteroid belt . It

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7748-635: The Hayden Planetarium in New York City displayed a Solar System model of only eight planets, which made headlines almost a year later. Ceres , Pallas , Juno and Vesta lost their planet status among most astronomers after the discovery of many other asteroids in the 1840s. On the other hand, planetary geologists often regarded Ceres, and less often Pallas and Vesta, as being different from smaller asteroids because they were large enough to have undergone geological evolution. Although

7897-470: The Kozai mechanism , which relates the eccentricity of an orbit to its inclination to a larger perturbing body—in this case, Neptune. Relative to Neptune, the amplitude of libration is 38°, and so the angular separation of Pluto's perihelion to the orbit of Neptune is always greater than 52° (90°–38°) . The closest such angular separation occurs every 10,000 years. Second, the longitudes of ascending nodes of

8046-581: The Lawrence Livermore National Laboratory studied irregularities in the motion of Halley's Comet . Brady claimed that they could have been caused by a Jupiter-sized planet beyond Neptune at 59 AU that is in a retrograde orbit around the Sun. However, both Marsden and Planet X proponent P. Kenneth Seidelmann attacked the hypothesis, showing that Halley's Comet randomly and irregularly ejects jets of material, causing changes to its own orbital trajectory, and that such

8195-638: The Lyapunov time of 10–20 million years, calculations become unreliable: Pluto is sensitive to immeasurably small details of the Solar System, hard-to-predict factors that will gradually change Pluto's position in its orbit. The semi-major axis of Pluto's orbit varies between about 39.3 and 39.6  AU with a period of about 19,951 years, corresponding to an orbital period varying between 246 and 249 years. The semi-major axis and period are presently getting longer. Despite Pluto's orbit appearing to cross that of Neptune when viewed from north or south of

8344-572: The New Horizons Radio Science Experiment (REX), the diameter was found to be 2 376 .6 ± 3.2 km . Pluto has a tenuous atmosphere consisting of nitrogen (N 2 ), methane (CH 4 ), and carbon monoxide (CO), which are in equilibrium with their ices on Pluto's surface. According to the measurements by New Horizons , the surface pressure is about 1  Pa (10  μbar ), roughly one million to 100,000 times less than Earth's atmospheric pressure. It

8493-641: The Universidad Complutense in Madrid suggested that the available data actually indicates more than one trans-Neptunian planet; subsequent work further suggests that the evidence is robust enough but rather than connected with the longitudes of the ascending nodes and the arguments of perihelia, semi-major axes and nodal distances could be the signposts. Additional work based on improved orbits of 39 objects still indicates that more than one perturber could be present and that one of them could orbit

8642-474: The University of Hawaiʻi calculated Pluto's albedo for the first time, finding that it matched that for methane ice; this meant Pluto had to be exceptionally luminous for its size and therefore could not be more than 1 percent the mass of Earth. (Pluto's albedo is 1.4–1.9 times that of Earth. ) In 1978, the discovery of Pluto's moon Charon allowed the measurement of Pluto's mass for the first time: roughly 0.2% that of Earth, and far too small to account for

8791-557: The giant planets ' orbits. These were taken to indicate the existence of yet another planet orbiting beyond Neptune. Even before Neptune's discovery, some speculated that one planet alone was not enough to explain the discrepancy. On 17 November 1834, the British amateur astronomer the Reverend Thomas John Hussey reported a conversation he had had with French astronomer Alexis Bouvard to George Biddell Airy ,

8940-400: The z axis . It was found that the hypothetical object's mass had to exceed 5 Earth masses to break the resonance, and the parameter space is quite large and a large variety of objects could have existed beyond Pluto without disturbing the resonance. Four test orbits of a trans-Plutonian planet have been integrated forward for four million years in order to determine the effects of such a body on

9089-663: The "planet" in a different position, and in 1878, CHF Peters , director of the Hamilton College Observatory in New York , showed that the star had not in fact vanished, and that the previous results had been due to human error. In 1879, Camille Flammarion noted that the comets 1862 III and 1889 III had aphelia of 47 and 49  AU , respectively, suggesting that they might mark the orbital radius of an unknown planet that had dragged them into an elliptical orbit. Astronomer George Forbes concluded on

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9238-402: The 2:3 mean-motion resonance). First, Pluto's argument of perihelion , the angle between the point where it crosses the ecliptic (or the invariant plane ) and the point where it is closest to the Sun, librates around 90°. This means that when Pluto is closest to the Sun, it is at its farthest north of the plane of the Solar System, preventing encounters with Neptune. This is a consequence of

9387-629: The British Astronomer Royal. Hussey reported that when he suggested to Bouvard that the unusual motion of Uranus might be due to the gravitational influence of an undiscovered planet, Bouvard replied that the idea had occurred to him, and that he had corresponded with Peter Andreas Hansen , director of the Seeberg Observatory in Gotha , about the subject. Hansen's opinion was that a single body could not adequately explain

9536-452: The Earth–Moon system (more than ten times its actual value), Rawlins's determination for Pluto's mass was similarly incorrect. It was nonetheless a meagre enough value for him to conclude Pluto was not Planet X. In 1976, Dale Cruikshank, Carl Pilcher, and David Morrison of the University of Hawaii analysed spectra from Pluto's surface and determined that it must contain methane ice , which

9685-699: The God of Death in Hinduism. Polynesian languages also tend to use the indigenous god of the underworld, as in Māori Whiro . Vietnamese might be expected to follow Chinese, but does not because the Sino-Vietnamese word 冥 minh "dark" is homophonous with 明 minh "bright". Vietnamese instead uses Yama, which is also a Buddhist deity, in the form of Sao Diêm Vương 星閻王 "Yama's Star", derived from Chinese 閻王 Yán Wáng / Yìhm Wòhng "King Yama". Once Pluto

9834-410: The IAU included Pluto, and Eris and its moon Dysnomia , in their Minor Planet Catalogue , giving them the official minor-planet designations "(134340) Pluto", "(136199) Eris", and "(136199) Eris I Dysnomia". Had Pluto been included upon its discovery in 1930, it would have likely been designated 1164, following 1163 Saga , which was discovered a month earlier. There has been some resistance within

9983-531: The Kuiper Cliff. Some of these new discoveries are close to the heliopause (120 AU) or well beyond it ( 2018 VG 18 , 2018 AG 37 , 2020 BE 102 , 2020 MK 53 ). An analysis of the TNO data available prior to September 2023 shows that there is a gap at about 72 AU, far from any mean-motion resonances with Neptune. Such a gap may have been induced by a massive perturber located further away. Tyche

10132-505: The Roman god of the underworld ; and it is also an epithet for Hades (the Greek equivalent of Pluto). Upon the announcement of the discovery, Lowell Observatory received over a thousand suggestions for names. Three names topped the list: Minerva , Pluto and Cronus . 'Minerva' was the Lowell staff's first choice but was rejected because it had already been used for an asteroid ; Cronus

10281-482: The Solar System, the two objects' orbits do not intersect. When Pluto is closest to the Sun, and close to Neptune's orbit as viewed from such a position, it is also the farthest north of Neptune's path. Pluto's orbit passes about 8 AU north of that of Neptune, preventing a collision. This alone is not enough to protect Pluto; perturbations from the planets (especially Neptune) could alter Pluto's orbit (such as its orbital precession ) over millions of years so that

10430-543: The Sun alone, but as part of a population of similarly sized objects. Pluto itself is now recognized as being a member of the Kuiper belt and the largest dwarf planet, larger than the more massive Eris. A number of astronomers, most notably Alan Stern , the head of NASA's New Horizons mission to Pluto, contend that the IAU's definition is flawed, and that Pluto and Eris, and all large trans-Neptunian objects, such as Makemake , Sedna , Quaoar , Gonggong and Haumea , should be considered planets in their own right. However,

10579-458: The Sun at 300-400 AU. On January 20, 2016, Brown and Konstantin Batygin published an article corroborating Trujillo and Sheppard's initial findings; proposing a super-Earth (dubbed Planet Nine ) based on a statistical clustering of the arguments of perihelia (noted before) near zero and also ascending nodes near 113° of six distant trans-Neptunian objects . They estimated it to be ten times

10728-496: The Sun, could explain the Kuiper cliff and the peculiar detached objects such as Sedna and 2012 VP 113 . Although some astronomers, such as Renu Malhotra and David Jewitt, have cautiously supported these claims, others, such as Alessandro Morbidelli, have dismissed them as "contrived". Malhotra & Volk (2017) argued that an unexpected variance in inclination for KBOs farther than the cliff at 50 AU (7.5 billion km; 4.6 billion mi) provided evidence of

10877-405: The Sun, where it can be easily observed. This means that unless its discovery was a freak accident, there is probably a substantial population of objects roughly Sedna's diameter yet to be observed in its orbital region. Mike Brown noted that Sedna is about three-quarters the size of Pluto. If there are sixty objects three-quarters the size of Pluto [out there] then there are probably forty objects

11026-483: The Sun. Light from the Sun takes 5.5 hours to reach Pluto at its orbital distance of 39.5 AU (5.91 billion km; 3.67 billion mi). Pluto's eccentric orbit periodically brings it closer to the Sun than Neptune , but a stable orbital resonance prevents them from colliding. Pluto has five known moons : Charon , the largest, whose diameter is just over half that of Pluto; Styx ; Nix ; Kerberos ; and Hydra . Pluto and Charon are sometimes considered

11175-561: The Sun; its orbit would be highly eccentric , and strongly inclined to the ecliptic—the planet's orbit would be at roughly a 32-degree angle from the orbital plane of the other known planets. This hypothesis was met with a mixed reception. Noted Planet X skeptic Brian G. Marsden of the Minor Planet Center pointed out that these discrepancies were a hundredth the size of those noticed by Le Verrier, and could easily be due to observational error. In 1972, Joseph Brady of

11324-497: The anti-Charon face of Pluto (around 180° longitude, where Tombaugh Regio 's western lobe, Sputnik Planitia , is located), whereas methane is most abundant near 300° east. The mountains are made of water ice. Pluto's surface is quite varied, with large differences in both brightness and color. Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturn 's moon Iapetus . The color varies from charcoal black, to dark orange and white. Pluto's color

11473-495: The astronomical community toward the reclassification, and in particular planetary scientists often continue to reject it, considering Pluto, Charon, and Eris to be planets for the same reason they do so for Ceres. In effect, this amounts to accepting only the second clause of the IAU definition. Alan Stern , principal investigator with NASA 's New Horizons mission to Pluto, derided the IAU resolution. He also stated that because less than five percent of astronomers voted for it,

11622-460: The astronomical community widely agrees that Planet X, as originally envisioned, does not exist, the concept of an as-yet-unobserved planet has been revived by a number of astronomers to explain other anomalies observed in the outer Solar System. As of March 2014, observations with the WISE telescope have ruled out the possibility of a Saturn -sized object (95 Earth masses) out to 10,000 AU , and

11771-486: The basis of this evidence that two planets must exist beyond Neptune. He calculated, based on the fact that four comets possessed aphelia at around 100 AU and a further six with aphelia clustered at around 300 AU, the orbital elements of a pair of hypothetical trans-Neptunian planets. These elements accorded suggestively with those made independently by another astronomer named David Peck Todd , suggesting to many that they might be valid. However, sceptics argued that

11920-596: The body to reorient itself, leading to its unusual axial tilt of 120°. The buildup of nitrogen is due to Pluto's vast distance from the Sun. At the equator, temperatures can drop to −240 °C (−400.0 °F; 33.1 K), causing nitrogen to freeze as water would freeze on Earth. The same polar wandering effect seen on Pluto would be observed on Earth were the Antarctic ice sheet several times larger. The plains on Pluto's surface are composed of more than 98 percent nitrogen ice , with traces of methane and carbon monoxide . Nitrogen and carbon monoxide are most abundant on

12069-547: The comet data and noted that Tyche, if it existed, would be detectable in the archive of data that was collected by NASA 's Wide-field Infrared Survey Explorer (WISE) telescope. In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist. The oligarch theory of planet formation states that there were hundreds of planet-sized objects, known as oligarchs, in

12218-472: The conception of these objects may differ considerably from that proposed by Lowell. When Sedna was discovered, its extreme orbit raised questions about its origin. Its perihelion is so distant (approximately 76 AU (11.4 billion km; 7.1 billion mi)) that no currently observed mechanism can explain Sedna's eccentric distant orbit. It is too far from the planets to have been affected by

12367-617: The decision was not representative of the entire astronomical community. Marc W. Buie , then at the Lowell Observatory, petitioned against the definition. Others have supported the IAU, for example Mike Brown , the astronomer who discovered Eris. Public reception to the IAU decision was mixed. A resolution introduced in the California State Assembly facetiously called the IAU decision a "scientific heresy". The New Mexico House of Representatives passed

12516-519: The discovery of 2012 VP 113 , a large object with a Sedna-like 4,200-year orbit and a perihelion of roughly 80 AU, which led them to suggest that it offered evidence of a potential trans-Neptunian planet. Trujillo and Sheppard argued that the orbital clustering of arguments of perihelia for 2012 VP 113 and other extremely distant TNOs suggests the existence of a " super-Earth " of between 2 and 15 Earth masses beyond 200 AU and possibly on an inclined orbit at 1,500 AU. In 2014 astronomers at

12665-502: The discovery of Eris did not rehabilitate the Planet ;X theory because it is far too small to have significant effects on the outer planets' orbits. Although most astronomers accept that Lowell's Planet X does not exist, a number have revived the idea that a large unseen planet could create observable gravitational effects in the outer Solar System. These hypothetical objects are often referred to as "Planet X", although

12814-477: The discrepancies in its orbit, and postulated the positions of two planets he believed were responsible. The second was launched when Gabriel Dallet suggested that a single trans-Neptunian planet lying at 47 AU could account for the motion of Uranus. Pickering agreed to examine plates for any suspected planets. In neither case were any found. In 1902, after observing the orbits of comets with aphelia beyond Neptune, Theodor Grigull of Münster , Germany proclaimed

12963-411: The discrepancies in the orbit of Uranus. Subsequent searches for an alternative Planet X, notably by Robert Sutton Harrington , failed. In 1992, Myles Standish used data from Voyager 2 ' s flyby of Neptune in 1989, which had revised the estimates of Neptune's mass downward by 0.5%—an amount comparable to the mass of Mars—to recalculate its gravitational effect on Uranus. With the new figures added in,

13112-461: The discrepancies, and with them the need for a Planet X, vanished. As of 2000 the majority of scientists agree that Planet X, as Lowell defined it, does not exist. Lowell had made a prediction of Planet X's orbit and position in 1915 that was fairly close to Pluto's actual orbit and its position at that time; Ernest W. Brown concluded soon after Pluto's discovery that this was a coincidence. From 1992 onward, many bodies were discovered orbiting in

13261-568: The earliest made by the Yerkes Observatory on August 20, 1909. Percival's widow, Constance Lowell, entered into a ten-year legal battle with the Lowell Observatory over her husband's legacy, and the search for Planet X did not resume until 1929. Vesto Melvin Slipher , the observatory director, gave the job of locating Planet X to 23-year-old Clyde Tombaugh , who had just arrived at the observatory after Slipher had been impressed by

13410-559: The early stages of the Solar System's evolution. In 2005, astronomer Eugene Chiang speculated that although some of these oligarchs became the planets we know today, most would have been flung outward by gravitational interactions. Some may have escaped the Solar System altogether to become free-floating planets , whereas others would be orbiting in a halo around the Solar System, with orbital periods of millions of years. This halo would lie at between 1,000 and 10,000 AU (150 and 1,500 billion km; 93 and 930 billion mi) from

13559-635: The ecliptic for other distant objects. He found hundreds of variable stars and asteroids , as well as two comets , but no further planets. To the observatory's disappointment and surprise, Pluto showed no visible disc; it appeared as a point, no different from a star, and, at only 15th magnitude, was six times dimmer than Lowell had predicted, which meant it was either very small, or very dark. Because of Lowell's predictions, astronomers thought that Pluto would be massive enough to perturb planets. This led them to assume that its albedo could be no less than 0.07 (meaning that, at minimum, it would reflect 7% of

13708-470: The existence of a Uranus-sized planet at 50 AU with a 360-year period, which he named Hades, cross-checking with the deviations in the orbit of Uranus. In 1921, Grigull revised his orbital period to 310–330 years, to better fit the observed deviations. In 1909, Thomas Jefferson Jackson See , an astronomer with a reputation as an egocentric contrarian, opined "there is certainly one, most likely two and possibly three planets beyond Neptune". Tentatively naming

13857-422: The first Kuiper belt objects discovered were quite small, objects increasingly closer in size to Pluto were soon discovered, some large enough (like Pluto itself) to satisfy geological but not dynamical ideas of planethood. On July 29, 2005, the debate became unavoidable when astronomers at Caltech announced the discovery of a new trans-Neptunian object , Eris , which was substantially more massive than Pluto and

14006-496: The first planet "Oceanus", he placed their respective distances at 42, 56 and 72 AU from the Sun. He gave no indication as to how he determined their existence, and no known searches were mounted to locate them. In 1911, Indian astronomer Venkatesh P. Ketakar suggested the existence of two trans-Neptunian planets, which he named after the Hindu gods Brahma and Vishnu , by reworking the patterns observed by Pierre-Simon Laplace in

14155-444: The first time Pluto is at perihelion (such as in 1989), Neptune is 57° ahead of Pluto. By Pluto's second passage through perihelion, Neptune will have completed a further one and a half of its own orbits, and will be 123° behind Pluto. Pluto and Neptune's minimum separation is over 17 AU, which is greater than Pluto's minimum separation from Uranus (11 AU). The minimum separation between Pluto and Neptune actually occurs near

14304-482: The giant planets, as roughly that of Earth; a value somewhat in accord with the 0.91 Earth mass calculated in 1942 by Lloyd R. Wylie at the US Naval Observatory , using the same assumptions. In 1949, Gerard Kuiper 's measurements of Pluto's diameter with the 200-inch telescope at Mount Palomar Observatory led him to the conclusion that it was midway in size between Mercury and Mars and that its mass

14453-412: The god and the planet inhabited "gloomy" regions, and the god was able to make himself invisible, as the planet had been for so long. The choice was further helped by the fact that the first two letters of Pluto were the initials of Percival Lowell; indeed, 'Percival' had been one of the more popular suggestions for a name for the new planet. Pluto's planetary symbol ⟨ [REDACTED] ⟩

14602-410: The gravitational pull of a large undiscovered object in the outer Solar System. Today, most astronomers agree that Planet X, as Lowell defined it, does not exist. After the discovery of Pluto and Charon, no more trans-Neptunian objects (TNOs) were found until 15760 Albion in 1992. Since then, thousands of such objects have been discovered. Most are now recognized as part of the Kuiper belt ,

14751-432: The gravity of Neptune or the other giant planets and too bound to the Sun to be affected by outside forces such as the galactic tides . Hypotheses to explain its orbit include that it was affected by a passing star, that it was captured from another planetary system , or that it was tugged into its current position by a trans-Neptunian planet. The most obvious solution to determining Sedna's peculiar orbit would be to locate

14900-406: The impact thought to have formed Sputnik Planitia , and showed that it might have been the result of liquid water upweling from below after the collision, implying the existence of a subsurface ocean at least 100 km deep. In June 2020, astronomers reported evidence that Pluto may have had a subsurface ocean , and consequently may have been habitable , when it was first formed. In March 2022,

15049-416: The light that hit it), which would have made Pluto about as dark as asphalt, and similar in reflectivity to the least reflective planet, which is Mercury . This would have given Pluto an estimated mass of no more than 70% that of Earth. Observations also revealed that Pluto's orbit was very elliptical, far more than that of any other planet. Almost immediately, some astronomers questioned Pluto's status as

15198-410: The mass of Earth (about 60% the mass of Neptune) with a semimajor axis of approximately 400–1500 AU . Even without gravitational evidence, Mike Brown, the discoverer of Sedna, has argued that Sedna's 12,000-year orbit means that probability alone suggests that an Earth-sized object exists beyond Neptune. Sedna's orbit is so eccentric that it spends only a small fraction of its orbital period near

15347-477: The mass of the Pluto–Charon system directly by observing the moon's orbital motion around Pluto. They determined Pluto's mass to be 1.31×10  kg; roughly one five-hundredth that of Earth or one-sixth that of the Moon, and far too small to account for the observed discrepancies in the orbits of the outer planets. Lowell's prediction had been a coincidence: If there was a Planet X, it was not Pluto. After 1978,

15496-467: The model predicted. He concluded that the simplest explanation was the gravitational pull of a distant planetary companion, such as a Neptune-sized object at 1,500 AU. This Neptune-sized object would cause the perihelia of objects with semi-major axes greater than 300 AU to oscillate, delivering them into planet-crossing orbits like those of (308933) 2006 SQ 372 and (87269) 2000 OO 67 or detached orbits like Sedna's. In 2014, astronomers announced

15645-525: The most massive object discovered in the Solar System since Triton in 1846. Its discoverers and the press initially called it the tenth planet , although there was no official consensus at the time on whether to call it a planet. Others in the astronomical community considered the discovery the strongest argument for reclassifying Pluto as a minor planet. The debate came to a head in August 2006, with an IAU resolution that created an official definition for

15794-561: The motion of Uranus, and postulated that two planets lay beyond Uranus. In 1848, Jacques Babinet raised an objection to Le Verrier's calculations, claiming that Neptune's observed mass was smaller and its orbit larger than Le Verrier had initially predicted. He postulated, based largely on simple subtraction from Le Verrier's calculations, that another planet of roughly 12 Earth masses, which he named "Hyperion", must exist beyond Neptune. Le Verrier denounced Babinet's hypothesis, saying, "[There is] absolutely nothing by which one could determine

15943-433: The observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The new object was later precovered on photographs dating back to 19 March 1915. The decision to name the object Pluto was intended in part to honour Percival Lowell, as his initials made up the word's first two letters. After discovering Pluto, Tombaugh continued to search

16092-466: The observatory's director, Vesto Melvin Slipher , summarily handed the job of locating the planet to Clyde Tombaugh , a 22-year-old Kansas farm boy who had only just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings. Tombaugh's task was to systematically capture sections of the night sky in pairs of images. Each image in a pair was taken two weeks apart. He then placed both images of each section in

16241-457: The orbit of Uranus, and hypothesised that they were caused by the gravitational pull of a yet-undiscovered planet. Le Verrier predicted the position of this new planet and sent his calculations to German astronomer Johann Gottfried Galle . On 23 September 1846, the night following his receipt of the letter, Galle and his student Heinrich d'Arrest discovered Neptune, exactly where Le Verrier had predicted. There remained some slight discrepancies in

16390-544: The orbital elements other than mean distance and period. It is not clear how Ketakar arrived at these figures, and his second planet, Vishnu, was never located. In 1894, with the help of William Pickering, Percival Lowell (a wealthy Bostonian) founded the Lowell Observatory in Flagstaff, Arizona . In 1906, convinced he could resolve the conundrum of Uranus's orbit, he began an extensive project to search for

16539-434: The orbits of objects like Sedna from Neptune. During Neptune's migration this planet is posited to have been captured in an outer resonance of Neptune and to have evolved into a higher perihelion orbit due to the Kozai mechanism leaving the remaining trans-Neptunian objects on stable orbits. In 2012, Rodney Gomes modelled the orbits of 92 Kuiper belt objects and found that six of those orbits were far more elongated than

16688-491: The orbits of the comets involved were still too uncertain to produce meaningful results. Some have considered Forbes's hypothesis a precursor to Planet Nine . In 1900 and 1901, Harvard College Observatory director William Henry Pickering led two searches for trans-Neptunian planets. The first was begun by Danish astronomer Hans Emil Lau who, after studying the data on the orbit of Uranus from 1690 to 1895, concluded that one trans-Neptunian planet alone could not account for

16837-419: The periods of Styx, Nix, Kerberos, and Hydra with that of Charon; the ratios become closer to being exact the further out the moons are. Ninth planet Clyde Tombaugh 's discovery of Pluto in 1930 appeared to validate Lowell's hypothesis, and Pluto was officially named the ninth planet. In 1978, Pluto was conclusively determined to be too small for its gravity to affect the giant planets, resulting in

16986-684: The planet's total mass downward by 0.5%—an amount comparable to the mass of Mars —to recalculate its gravitational effect on Uranus. When Neptune's newly determined mass was used in the Jet Propulsion Laboratory Developmental Ephemeris (JPL DE), the supposed discrepancies in the Uranian orbit, and with them the need for a Planet X, vanished. There are no discrepancies in the trajectories of any space probes such as Pioneer 10 , Pioneer 11 , Voyager 1 , and Voyager 2 that can be attributed to

17135-467: The planetary satellites of Jupiter and applying them to the outer planets. The three inner Galilean moons of Jupiter, Io , Europa and Ganymede , are locked in a complicated 1:2:4 resonance called a Laplace resonance . Ketakar suggested that Uranus, Neptune and his hypothetical trans-Neptunian planets were also locked in Laplace-like resonances. This is incorrect; Uranus and Neptune, while in

17284-546: The position of another planet, barring hypotheses in which imagination played too large a part." In 1850 James Ferguson , Assistant Astronomer at the United States Naval Observatory , noted that he had "lost" a star he had observed, GR1719k, which Lt. Matthew Maury, the superintendent of the Observatory, claimed was evidence that it must be a new planet. Subsequent searches failed to recover

17433-531: The possibility of an object with a mass similar to that of Earth located farther than 100 AU (15 billion km; 9.3 billion mi) with an eccentric and inclined orbit. Computer simulations by Patryk Lykawka of Kobe University have suggested that an object with a mass between 0.3~0.7  M E , ejected outward by Neptune early in the Solar System's formation and currently in an elongated orbit between 101 and 200 AU (15.1 and 29.9 billion km; 9.4 and 18.6 billion mi) from

17582-422: The presence of an object with a mass between those of Mars and Earth located beyond 48 AU. The presence of an object with a mass similar to that of Mars in a circular orbit at 60 AU (9.0 billion km; 5.6 billion mi) leads to a trans-Neptunian object population incompatible with observations. For instance, it would severely deplete the plutino population. Astronomers have not excluded

17731-414: The same term [REDACTED] This disambiguation page lists articles associated with the title Plutonian . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Plutonian&oldid=985139232 " Category : Disambiguation pages Hidden categories: Short description

17880-426: The same volume as Pluto, showing that Pluto is part of a population of objects called the Kuiper belt . This made its official status as a planet controversial, with many questioning whether Pluto should be considered together with or separately from its surrounding population. Museum and planetarium directors occasionally created controversy by omitting Pluto from planetary models of the Solar System . In February 2000

18029-473: The search for Planet X. Failing to find the planet, according to one friend, "virtually killed him". Lowell's widow, Constance, engaged in a legal battle with the observatory over Lowell's legacy which halted the search for Planet X for several years. In 1925, the observatory obtained glass discs for a new 13 in (33 cm) wide-field telescope to continue the search, constructed with funds from Abbott Lawrence Lowell , Percival's brother. In 1929

18178-428: The size of Pluto ... If there are forty objects the size of Pluto, then there are probably ten that are twice the size of Pluto. There are probably three or four that are three times the size of Pluto, and the biggest of these objects ... is probably the size of Mars or the size of the Earth. However, Brown notes that even though it might approach or exceed Earth in size, should such an object be found it would still be

18327-628: The stability of the Neptune–Pluto 3:2 resonance. Planets beyond Pluto with masses of 0.1 and 1.0 Earth masses in orbits at 48.3 and 75.5 AU, respectively, do not disturb the 3:2 resonance. Test planets of 5 Earth masses with semi-major axes of 52.5 and 62.5 AU disrupt the four-million-year libration of Pluto's argument of perihelion. Harrington died in January 1993, without having found Planet X. Six months before, E. Myles Standish had used data from Voyager 2' s 1989 flyby of Neptune, which had revised

18476-508: The structure of the residuals of Uranus' longitude using a trigonometric formula, Ernest W. Brown asserted (in agreement with E. C. Bower ) that the presumed irregularities in the orbit of Uranus could not be due to the gravitational effect of a more distant planet, and thus that Lowell's supposed prediction was "purely accidental". Throughout the mid-20th century, estimates of Pluto's mass were revised downward. In 1931, Nicholson and Mayall calculated its mass, based on its supposed effect on

18625-428: The suggestion to astronomy professor Herbert Hall Turner , who cabled it to colleagues at Lowell on March 16, three days after the announcement. The name 'Pluto' was mythologically appropriate: the god Pluto was one of six surviving children of Saturn , and the others had already all been chosen as names of major or minor planets (his brothers Jupiter and Neptune , and his sisters Ceres , Juno and Vesta ). Both

18774-418: The surface of Mars were canals constructed by an intelligent civilization . Lowell's first search focused on the ecliptic , the plane encompassed by the zodiac where the other planets in the Solar System lie. Using a 5-inch photographic camera, he manually examined over 200 three-hour exposures with a magnifying glass, and found no planets. At that time Pluto was too far above the ecliptic to be imaged by

18923-408: The survey. After revising his predicted possible locations, Lowell conducted a second search from 1914 to 1916. In 1915, he published his Memoir of a Trans-Neptunian Planet , in which he concluded that Planet X had a mass roughly seven times that of Earth—about half that of Neptune —and a mean distance from the Sun of 43 AU. He assumed Planet X would be a large, low-density object with

19072-414: The tenth was " interstellar cirrus "; none were found to be Solar System bodies. In 1988, A. A. Jackson and R. M. Killen studied the stability of Pluto's resonance with Neptune by placing test "Planet X-es" with various masses and at various distances from Pluto. Pluto and Neptune's orbits are in a 3:2 resonance, which prevents their collision or even any close approaches, regardless of their separation in

19221-455: The term planet to exclude dwarf planets such as Pluto. Many planetary astronomers, however, continue to consider Pluto and other dwarf planets to be planets. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analyzing perturbations in the orbit of Uranus . Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranus's orbit

19370-550: The term "planet". According to this resolution, there are three conditions for an object in the Solar System to be considered a planet: Pluto fails to meet the third condition. Its mass is substantially less than the combined mass of the other objects in its orbit: 0.07 times, in contrast to Earth, which is 1.7 million times the remaining mass in its orbit (excluding the moon). The IAU further decided that bodies that, like Pluto, meet criteria 1 and 2, but do not meet criterion 3 would be called dwarf planets . In September 2006,

19519-430: The term has not seen significant use. Pluto's orbital period is about 248 years. Its orbital characteristics are substantially different from those of the planets, which follow nearly circular orbits around the Sun close to a flat reference plane called the ecliptic . In contrast, Pluto's orbit is moderately inclined relative to the ecliptic (over 17°) and moderately eccentric (elliptical). This eccentricity means

19668-510: The time of Pluto's aphelion. The 2:3 resonance between the two bodies is highly stable and has been preserved over millions of years. This prevents their orbits from changing relative to one another, so the two bodies can never pass near each other. Even if Pluto's orbit were not inclined, the two bodies could never collide. When Pluto's period is slightly different from 3/2 of Neptune's, the pattern of its distance from Neptune will drift. Near perihelion Pluto moves interior to Neptune's orbit and

19817-565: The two bodies—the points where they cross the invariant plane —are in near-resonance with the above libration. When the two longitudes are the same—that is, when one could draw a straight line through both nodes and the Sun—Pluto's perihelion lies exactly at 90°, and hence it comes closest to the Sun when it is furthest north of Neptune's orbit. This is known as the 1:1 superresonance . All the Jovian planets (Jupiter, Saturn, Uranus, and Neptune) play

19966-477: The way that a body's spin will always adjust to minimize energy. This could mean a body reorienting itself to put extraneous mass near the equator and regions lacking mass tend towards the poles. This is called polar wander . According to a paper released from the University of Arizona, this could be caused by masses of frozen nitrogen building up in shadowed areas of the dwarf planet. These masses would cause

20115-434: The western lobe of the "Heart", is a 1,000 km-wide basin of frozen nitrogen and carbon monoxide ices, divided into polygonal cells, which are interpreted as convection cells that carry floating blocks of water ice crust and sublimation pits towards their margins; there are obvious signs of glacial flows both into and out of the basin. It has no craters that were visible to New Horizons , indicating that its surface

20264-433: The winds blowing from the center of Sputnik Planitia in the direction of surrounding mountains. The dune wavelengths are in the range of 0.4–1 km and likely consist of methane particles 200–300 μm in size. Pluto's density is 1.853 ± 0.004 g/cm . Because the decay of radioactive elements would eventually heat the ices enough for the rock to separate from them, scientists expect that Pluto's internal structure

20413-522: The word of the year. To "pluto" is to "demote or devalue someone or something". In April 2024, Arizona (where Pluto was first discovered in 1930) passed a law naming Pluto as the official state planet. Researchers on both sides of the debate gathered in August 2008, at the Johns Hopkins University Applied Physics Laboratory for a conference that included back-to-back talks on the IAU definition of

20562-411: Was a hypothetical gas giant proposed to be located in the Solar System 's Oort cloud . It was first proposed in 1999 by astrophysicists John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette . They argued that evidence of Tyche's existence could be seen in a supposed bias in the points of origin for long-period comets . In 2013, Matese and Whitmire re-evaluated

20711-464: Was appearing less gradually from behind Pluto's disc, indicating a thinning atmosphere. The presence of methane, a powerful greenhouse gas , in Pluto's atmosphere creates a temperature inversion , with the average temperature of its atmosphere tens of degrees warmer than its surface, though observations by New Horizons have revealed Pluto's upper atmosphere to be far colder than expected (70 K, as opposed to about 100 K). Pluto's atmosphere

20860-755: Was being disturbed by another planet besides Neptune. In 1906, Percival Lowell —a wealthy Bostonian who had founded Lowell Observatory in Flagstaff, Arizona , in 1894—started an extensive project in search of a possible ninth planet, which he termed " Planet X ". By 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search, using mathematical calculations made by Elizabeth Williams , until his death in 1916, but to no avail. Unknown to Lowell, his surveys had captured two faint images of Pluto on March 19 and April 7, 1915, but they were not recognized for what they were. There are fourteen other known precovery observations, with

21009-592: Was disfavored because it was promoted by an unpopular and egocentric astronomer, Thomas Jefferson Jackson See . A vote was then taken and 'Pluto' was the unanimous choice. To make sure the name stuck, and that the planet would not suffer changes in its name as Uranus had, Lowell Observatory proposed the name to the American Astronomical Society and the Royal Astronomical Society ; both approved it unanimously. The name

21158-497: Was found, its faintness and lack of a viewable disc cast doubt on the idea that it was Lowell's Planet X . Estimates of Pluto's mass were revised downward throughout the 20th century. Astronomers initially calculated its mass based on its presumed effect on Neptune and Uranus. In 1931, Pluto was calculated to be roughly the mass of Earth , with further calculations in 1948 bringing the mass down to roughly that of Mars . In 1976, Dale Cruikshank, Carl Pilcher and David Morrison of

21307-442: Was immediately hailed as the ninth planet , but it never fit well with the other eight, and its planetary status was questioned when it was found to be much smaller than expected. These doubts increased following the discovery of additional objects in the Kuiper belt starting in the 1990s, and particularly the more massive scattered disk object Eris in 2005. In 2006, the International Astronomical Union (IAU) formally redefined

21456-437: Was initially thought that, as Pluto moves away from the Sun, its atmosphere should gradually freeze onto the surface; studies of New Horizons data and ground-based occultations show that Pluto's atmospheric density increases, and that it likely remains gaseous throughout Pluto's orbit. New Horizons observations showed that atmospheric escape of nitrogen to be 10,000 times less than expected. Alan Stern has contended that even

21605-434: Was most probably about 0.1 Earth mass. In 1973, based on the similarities in the periodicity and amplitude of brightness variation with Triton , Dennis Rawlins conjectured Pluto's mass must be similar to Triton's. In retrospect, the conjecture turns out to have been correct; it had been argued by astronomers Walter Baade and E.C. Bower as early as 1934. However, because Triton's mass was then believed to be roughly 2.5% of

21754-517: Was named after Uranus, and neptunium , which was named after Neptune. Most languages use the name "Pluto" in various transliterations. In Japanese, Houei Nojiri suggested the calque Meiōsei ( 冥王星 , "Star of the King (God) of the Underworld") , and this was borrowed into Chinese and Korean. Some languages of India use the name Pluto, but others, such as Hindi , use the name of Yama ,

21903-481: Was published on May 1, 1930. The name Pluto had received some 150 nominations among the letters and telegrams sent to Lowell. The first had been from Venetia Burney (1918–2009), an eleven-year-old schoolgirl in Oxford , England, who was interested in classical mythology . She had suggested it to her grandfather Falconer Madan when he read the news of Pluto's discovery to his family over breakfast; Madan passed

22052-442: Was soon embraced by wider culture. In 1930, Walt Disney was apparently inspired by it when he introduced for Mickey Mouse a canine companion named Pluto , although Disney animator Ben Sharpsteen could not confirm why the name was given. In 1941, Glenn T. Seaborg named the newly created element plutonium after Pluto, in keeping with the tradition of naming elements after newly discovered planets, following uranium , which

22201-412: Was then created as a monogram of the letters "PL". This symbol is rarely used in astronomy anymore, though it is still common in astrology. However, the most common astrological symbol for Pluto, occasionally used in astronomy as well, is an orb (possibly representing Pluto's invisibility cap) over Pluto's bident ⟨ [REDACTED] ⟩ , which dates to the early 1930s. The name 'Pluto'

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