1.
Geography of Pluto
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The geography of Pluto entails the delineation and characterization of regions on Pluto. Plutonian geography is focused on what is called physical geography on Earth, that is. On 14 July 2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto, during its brief flyby, New Horizons made detailed geographical measurements and observations of Pluto and its moons. Pluto may be defined as having retrograde rotation and a tilt of 60 degrees, or prograde rotation. Following the latter convention, the currently in daylight is the northern one. This is the used by the International Astronomical Union and the New Horizons team. However, older sources may define Plutos rotation as retrograde and therefore the sunlit side as the southern hemisphere, east and west are also swapped between the two conventions. The following names are names and nicknames, proposed by the New Horizons discovery team. They were taken from various deities or demons, some from ancient mythology and others from modern popular culture. Cthulhu Regio, nicknamed The Whale after its shape, is an elongated and it is 2,990 km long and is the largest dark feature on Pluto. Tombaugh Regio, nicknamed The Heart, is a large, light-colored region in the shape of a named after the discoverer of Pluto. Two lobes of the heart are distinct geological features sharing a bright appearance, the heart is about 1,590 km across. The region contains 3,400 m mountains made of ice, Hillary Montes and Norgay Montes. The lack of craters suggests that its there is less than 100 million years old. Subsequent data indicated that features near the edges of the region show evidence of ice flow such as glaciers, a series of semi-regularly spaced dark spots with irregular boundaries are nicknamed the Brass Knuckles. They average about 480 km in diameter and are located along the equator between the Heart and the tail of the Whale, the brass knuckles are separated from one another by tall uplands. There are also many canyons running through them and through the mountains that are hundreds of miles long. It does not appear as a ring in higher-resolution images, the prime meridian of Pluto is defined as the longitude facing Charon
2.
Pluto
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Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered, Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered and this led the International Astronomical Union to define the term planet formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet, Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has an eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, light from the Sun takes about 5.5 hours to reach Pluto at its average distance. Pluto has five moons, Charon, Styx, Nix, Kerberos. Pluto and Charon are sometimes considered a system because the barycenter of their orbits does not lie within either body. The IAU has not formalized a definition for binary dwarf planets, on July 14,2015, the New Horizons spacecraft became the first spacecraft to fly by Pluto. During its brief flyby, New Horizons made detailed measurements and observations of Pluto, on October 25,2016, at 05,48 pm ET, the last bit of data was received from New Horizons from its close encounter with Pluto on July 14,2015. In the 1840s, Urbain Le Verrier used Newtonian mechanics to predict the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century led astronomers to speculate that Uranuss orbit was being disturbed by another planet besides Neptune, by 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, 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 prediscovery observations, with the oldest made by the Yerkes Observatory on August 20,1909. Percivals widow, Constance Lowell, entered into a legal battle with the Lowell Observatory over her late husbands legacy. Tombaughs task was to image the night sky in pairs of photographs, then examine each pair
3.
Geographic coordinate system
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A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position. A common choice of coordinates is latitude, longitude and elevation, to specify a location on a two-dimensional map requires a map projection. The invention of a coordinate system is generally credited to Eratosthenes of Cyrene. Ptolemy credited him with the adoption of longitude and latitude. Ptolemys 2nd-century Geography used the prime meridian but measured latitude from the equator instead. Mathematical cartography resumed in Europe following Maximus Planudes recovery of Ptolemys text a little before 1300, in 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, the Dominican Republic voted against the motion, while France and Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911, the latitude of a point on Earths surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the equator, the north pole is 90° N, the south pole is 90° S. The 0° parallel of latitude is designated the equator, the plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres, the longitude of a point on Earths surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses, which converge at the north and south poles, the prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side. The antipodal meridian of Greenwich is both 180°W and 180°E, the combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The grid formed by lines of latitude and longitude is known as a graticule, the origin/zero point of this system is located in the Gulf of Guinea about 625 km south of Tema, Ghana. To completely specify a location of a feature on, in, or above Earth. Earth is not a sphere, but a shape approximating a biaxial ellipsoid. It is nearly spherical, but has an equatorial bulge making the radius at the equator about 0. 3% larger than the radius measured through the poles, the shorter axis approximately coincides with the axis of rotation
4.
Maya death gods
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Hunhau is the lord of the Underworld. Iconographically, Hunhau and Uacmitun Ahau correspond to the Gods A and A and this death god inhabits an Underworld that is also the world of the dead. As a ruler over the world of the dead, the death god corresponds to the Aztec deity Mictlantecuhtli. The Popol Vuh has two leading death gods, but these two are one, Both are called Death, but while one is known as One Death. They were vanquished by the Hero Twins, the two principal death gods count among the many were-animals and spooks inhabiting the Underworld, with the God A way in particular manifesting himself as a head hunter and a deer hunter. Kisin is the name of the death god among the Lacandons as well as the early colonial Choles, kis being a root with meanings like flatulence, other names include Yum Kimil, Lord of Death in Yucatán and Pukuh in Chiapas. The name Hun Ahau appears frequently in the Ritual of the Bacabs, ah Puch, though often mentioned in books about the Mayas, does not appear to be an authentic Maya name for the death god. In the Popol Vuh, the Hero Twins descend to the Place of Fright and they defeat the Death Gods and put restrictions on their cult. According to one of the earliest sources on Maya religion, Eopuco mistreated and killed the Bacab, Both God A and God A figure prominently in the New Year rites depicted in the Dresden Codex. God A probably corresponds to the death god Uacmitun Ahau in Landas description of the New year rites and he presides over a year of great mortality. To ward off evil during this year, men would walk over a bed of glowing embers that possibly represented the fires of the Underworld, the death god classified as God A always has a fleshless skull, usually with a skeletal body. He often occurs in the following contexts, with varying hieroglyphic names and attributes, God A figures in processions and random arrays of were-animals and spooks. In connection with these apparitions, he tends to be depicted either as a hunter or as deer hunter. On the grandiose Tonina stucco wall, the head is that of an enemy king. The death gods deer hunt has two sides, on the one hand, this deer hunt may metaphorically refer to a hunt for human victims. On the other hand, there seems to be a connection with certain wayob shaped like deer. On the famous peccary skull from Copan, for example, such a deer way appears to be welcoming the death god returning from a hunt and this may relate to the fact that in Yucatán, one of the four Bacabs was called White Death. The other codical death god is God A, corresponding to Landas Uac Mitun Ahau, and characterized by a black stripe over the eyes, just like death god A, he figures among the Classic wayob
5.
Popol Vuh
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Popol Vuh is a corpus of mytho-historical narratives of the Post Classic Kiche kingdom in Guatemalas western highlands. The title translates as Book of the Community, Book of Counsel, Popol Vuhs prominent features are its creation myth, its diluvian suggestion, its epic tales of the Hero Twins Hunahpú and Xbalanqué, and its genealogies. The myth begins with the exploits of anthropomorphic ancestors and concludes with a regnal genealogy, as with other texts, a great deal of Popol Vuhs significance lies in the scarcity of early accounts dealing with Mesoamerican mythologies. Popol Vuhs fortuitous survival is attributable to the Spanish 18th century Dominican friar Francisco Ximénez, Popol Vuh encompasses a range of subjects that includes creation, ancestry, history, and cosmology. Part 1 Account of the creation of living beings, animals are created first followed by humans. The first humans of earth and mud soak up water and dissolve, the second humans are created from wood, but they did not have souls, nor minds. They lose favor with the gods who cause them to be beaten, exploits of hero twins Hunahpú and Xbalanqué also known as Hunter and Jaguar deer. Their defeat of Vucub-Caquix and his sons Zipacná and Cabracán, presentation of ball-game motif, part 2 Lineage of principal figures. Xpiyacoc and Xmucané beget Hun Hunahpú and Vucub Hunahpú, Hun Hunahpú and Xbaquiyalo beget Hunbatz, demise of Hun Hunahpú and Vucub Hunahpú and origin of hero twins Hunahpú and Xbalanqué. They are summoned to the underworld of Xibalbá for playing their ball game too noisily and they are killed, Hun Hunahpús head is placed in a calabash tree. This skull later impregnates Xquic, daughter of a Xibalbé lord and she flees the lords and lives with Xmucané where she gives birth to Hero Twins Hunahpú and Xbalanqué. Mistreated by their half-brothers Hunbatz and Huchouén, Hunahpú and Xbalanqué trick them into climbing a tree, Hunbatz and Huchouén transform into monkeys. Rediscovery of ball game and defeat of the lords of Xibalbá, upon finding the fathers equipment suspended from the ceiling, Hunahpú and Xbalanqué are also summoned to Xibalbá for playing too boisterously. They outwit the lords and ascend to the sky as constellations. Part 3 Creation of humans, migration, and first dawn, animals gather white and yellow corn from which the gods create Balam-Quitze, Jaguar Night, Naught, and Wind Jaguar. Their four wives are later created while they sleep and their descendants travel to Tulán Zuiva to await the first dawn. The god Tohil gives fire, but it is extinguished by hail, Tohil requires concessions to restore their fire, but the Kiche hide themselves in smoke and obtain their fire without conditions. The Kiche rise to prominence over the other tribes, the first dawn appears, dries out the land, and turns original animals to stone
6.
Cthulhu Regio
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Cthulhu Regio /kəˈθuːluː, ˈkθuː- ˈrɛdʒi. oʊ/ is a prominent surface feature of the dwarf planet Pluto, that is reminiscent of a whale in shape. It is a dark region along Plutos equator,2,990 km long. It is west of the Sputnik Planitia region of Tombaugh Regio, also known as Plutos heart, and to the east of Meng-Po, as of 30 July 2015, the eastern head region had been imaged in much higher resolution than the western tail region. NASA initially referred to it as the Whale in reference to its overall shape, by 14 July 2015, the provisional name Cthulhu was being used by the New Horizons team. It was named after the deity from the works of H. P. Lovecraft. The character Cthulhu initially appeared in Lovecrafts 1928 short story The Call of Cthulhu and it is the subject of worship by a number of human cults asserting that while it is currently trapped, Cthulhu will eventually return. Cthulhu was the most popular name in this category of the poll, the name received positive reaction from the press and social media, with a Chicago Tribune editorial supporting the name and its democratic origin. The name Cthulhu may be submitted to the IAU as an official name, Cthulhu Regio contains many craters and linear features that have also been given informal names. Geography of Pluto Media related to Cthulhu Regio at Wikimedia Commons
7.
Vucub-Came Macula
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Vucub-Came is one of the Brass Knuckles, a series of equatorial dark regions on Pluto. It is named after Wuquub Kameh Seven Death, one of the Quiché death gods in the Popol Vuh, Vucub-Came Macula is the fourth-largest dark spot on Pluto. Its surface is covered with tholins which give Vucub-Came its brown color, the dark spot is surrounded with tall uplands. Extensive fault systems in this area have formed deep canyons running roughly north–south
8.
The New York Times
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The New York Times is an American daily newspaper, founded and continuously published in New York City since September 18,1851, by The New York Times Company. The New York Times has won 119 Pulitzer Prizes, more than any other newspaper, the papers print version in 2013 had the second-largest circulation, behind The Wall Street Journal, and the largest circulation among the metropolitan newspapers in the US. The New York Times is ranked 18th in the world by circulation, following industry trends, its weekday circulation had fallen in 2009 to fewer than one million. Nicknamed The Gray Lady, The New York Times has long been regarded within the industry as a newspaper of record. The New York Times international version, formerly the International Herald Tribune, is now called the New York Times International Edition, the papers motto, All the News Thats Fit to Print, appears in the upper left-hand corner of the front page. On Sunday, The New York Times is supplemented by the Sunday Review, The New York Times Book Review, The New York Times Magazine and T, some other early investors of the company were Edwin B. Morgan and Edward B. We do not believe that everything in Society is either right or exactly wrong, —what is good we desire to preserve and improve, —what is evil, to exterminate. In 1852, the started a western division, The Times of California that arrived whenever a mail boat got to California. However, when local California newspapers came into prominence, the effort failed, the newspaper shortened its name to The New-York Times in 1857. It dropped the hyphen in the city name in the 1890s, One of the earliest public controversies it was involved with was the Mortara Affair, the subject of twenty editorials it published alone. At Newspaper Row, across from City Hall, Henry Raymond, owner and editor of The New York Times, averted the rioters with Gatling guns, in 1869, Raymond died, and George Jones took over as publisher. Tweed offered The New York Times five million dollars to not publish the story, in the 1880s, The New York Times transitioned gradually from editorially supporting Republican Party candidates to becoming more politically independent and analytical. In 1884, the paper supported Democrat Grover Cleveland in his first presidential campaign, while this move cost The New York Times readership among its more progressive and Republican readers, the paper eventually regained most of its lost ground within a few years. However, the newspaper was financially crippled by the Panic of 1893, the paper slowly acquired a reputation for even-handedness and accurate modern reporting, especially by the 1890s under the guidance of Ochs. Under Ochs guidance, continuing and expanding upon the Henry Raymond tradition, The New York Times achieved international scope, circulation, in 1910, the first air delivery of The New York Times to Philadelphia began. The New York Times first trans-Atlantic delivery by air to London occurred in 1919 by dirigible, airplane Edition was sent by plane to Chicago so it could be in the hands of Republican convention delegates by evening. In the 1940s, the extended its breadth and reach. The crossword began appearing regularly in 1942, and the section in 1946
9.
Tombaugh Regio
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Tombaugh Regio /ˈtɒmbaʊ ˈrɛdʒi. oʊ/, nicknamed The Heart after its shape, is the largest bright surface feature of the dwarf planet Pluto. It is just north of the equator, to the northeast of Cthulhu Regio and to the northwest of Krun Macula and its western lobe, a 1000 km-wide plain of nitrogen and other ices, is named Sputnik Planitia. The eastern lobe is thought to consist of high-albedo uplands coated by nitrogen transported through the atmosphere from Sputnik Planitia, some of this nitrogen ice then returns to Sputnik Planitia via glacial flow. It is named after Clyde Tombaugh, the discoverer of Pluto, Tombaugh Regio is a large, light-colored region about 1,590 km across. The two lobes of the feature are geologically distinct, the western lobe, Sputnik Planitia, is smoother than the eastern, and they are of slightly different colors. Early speculation was that the western lobe may be an impact crater filled with nitrogen snow. Bright spots within the region were initially speculated to be mountain peaks, photos, released on 15 July 2015, revealed 3,400 m mountains made of water ice in the feature, they also showed no craters in this same region. The surface of Sputnik Planitia is divided into polygonal convection cells and is less than 10 million years old, indicating that Pluto is geologically active. The feature had been identified as a spot for six decades prior to the New Horizons flyby. Over these six decades the spot had been observed to be dimming, Tombaugh Regio was first identified in the initial image of Pluto returned after the New Horizons probe recovered from an anomaly that temporarily sent it into safe mode. NASA initially referred to it as a heart in reference to its overall shape, on 15 July 2015, the region was named Tombaugh Regio by the New Horizons team in honor of astronomer Clyde Tombaugh, the discoverer of Pluto, regio being Latin for region. Some people find the feature also resembles the Disney character Pluto, the Walt Disney Company acknowledged this perceived likeness in a short animation. Geography of Pluto List of geological features on Pluto Media related to Tombaugh Regio at Wikimedia Commons
10.
Coleta de Dados Colles
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The Coleta de Dados Colles are a cluster of hills on the smooth plains of Sputnik Planitia on Pluto. They actually represent blocks of ice floating in the denser nitrogen ice of the planitia. The hills were named in July 28,2015 by the research team of the New Horizons mission after the first Brazilian satellite. So, the name means Data Collecting Colles. The name has yet to be recognized by the IAU, um satélite brasileiro em Plutão Primeiro satélite nacional nomeia região em Plutão
11.
Hillary Montes
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The Hillary Montes /ˈhɪləri ˈmɒntiːz/ are mountains that reach 1.6 km above the surface of the dwarf planet Pluto. They are located northwest of Norgay Montes in the southwest border area of Sputnik Planitia in the south of Tombaugh Regio, the Hillary Montes were first viewed by the New Horizons spacecraft on 14 July 2015, and announced by NASA on 24 July 2015. The Hillary Montes rise to 1.6 km high, about half as high as the Norgay Montes, the Hillary Montes are similar in height to that of the peak of Mount Sněžka, the highest mountain in the Czech Republic, above sea level. Other mountains of height are Mount Katahdin in Maine, USA. Geography of Pluto Geology of Pluto List of geological features on Pluto List of tallest mountains in the Solar System NASA Pluto factsheet NASA Official homepage New Horizons homepage
12.
Sputnik Planitia
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Sputnik Planitia /ˈspʌtnɪk pləˈnɪʃiə/, originally Sputnik Planum, is a high-albedo ice-covered basin on Pluto, about 1,050 by 800 km in size. It lies mostly in the hemisphere, but extends across the equator. Much of it has a surface of irregular polygons separated by troughs, the polygons are on average about 33 km across. In some cases troughs are populated by blocky mountains or hills, Sputnik Planitia constitutes the western lobe of the heart-shaped Tombaugh Regio. There appear to be wind streaks on the surface evidence of sublimation. The dark streaks are a few kilometers long and all aligned in the same direction, the basin also contains pits that have possibly formed by sublimation. Sputnik Planitia is named after Earths first artificial satellite, the planitia has no craters that were detectable by New Horizons, leading to the conclusion that its surface must be less than 10 million years old. The ice composing the basin is thought to consist primarily of ice, with smaller fractions of carbon monoxide and methane ice. At Plutos ambient temperature of 38 K, nitrogen and carbon monoxide ices are denser and much less rigid water ice, making glacial-like flows possible. Sputnik Planitia may have originated as a basin that subsequently collected volatile ices. Alternatively, it has suggested that the accumulation of ices in this location depressed the surface there. The accumulation of several kilometers of ice in the basin was in part a consequence of its higher surface pressure. The positive temperature gradient of Plutos atmosphere contributes to making a topographic depression a cold trap, a high seasonal thermal inertia of Plutos surface is an important driver of deposition of nitrogen ice at low latitudes. These latitudes receive less insolation than Plutos polar regions due to its high obliquity. However, other effects of an event could have also contributed to such an anomaly. A positive gravity anomaly could have caused polar wander, reorienting the spin axis of Pluto to put the planitia near the Pluto-Charon tidal axis, Sputnik Planitia is presently close to the anti-Charon point on Pluto, a result that has less than a 5% probability of arising by chance. Gradual freezing of such an ocean, in combination with polar wander, convection cells have about 100 m of vertical relief, with the highest points being at their centers. Modeling of nitrogen ice convection cells suggests a depth of one tenth their width, or 3–4 km for most of the planitia
13.
Luna Linea
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The geological features on Pluto are being identified by scientists working with data from the New Horizons spacecraft. The International Astronomical Union has determined that the names for these features will be chosen from the themes, Names for the underworld from the worlds mythologies. Gods, goddesses, and dwarfs associated with the underworld, heroes and other explorers of the underworld. Writers associated with Pluto and the Kuiper belt, scientists and engineers associated with Pluto and the Kuiper belt. The following is a list of names chosen by the New Horizons team. Not all of the names correspond with the themes listed above, a cavus is a hollow or steep-sided depression. One cavus has been identified on Pluto thus far, it is named after a mythological underworld, Plutonian colles are being named after spacecraft that operated in Earth orbit. Plutonian craters are being named after scientists and other associated with the study of Pluto. Plutonian dorsa are being named after underworlds in mythology, a fossa is a ditch-like feature. Plutonian fossae are being named after figures associated with underworld myths, a linea is an elongated marking. Plutonian lineae are being named after space probes, Plutonian maculae are being named after underworld creatures from fiction and mythology. Plutonian montes are being named after explorers and adventurers, a planum is a plateau or high plain. One was initially identified on Pluto, but it has since been recognized to be a planitia, a planitia is a low plain, distinct from plana as they are located on lower terrain. A regio is a geographically distinct from its surroundings. Plutonian regiones are being named after underworld spirits in fiction and mythology, Plutonian rupēs are being named after explorers. A terra is an extensive landmass, Plutonian terrae are being named after space probes. The lone Plutonian vallis identified thus far is named after an explorer, geography of Pluto Geology of Pluto List of geological features on Charon
14.
Atmosphere of Pluto
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The atmosphere of Pluto is the tenuous layer of gases surrounding Pluto. It consists mainly of nitrogen, with amounts of methane and carbon monoxide. It contains layered haze, probably consisting of compounds which form from these gases due to high-energy radiation. The atmosphere of Pluto is notable for its strong and not completely clear seasonal changes caused by peculiarities of the orbital and axial rotation of Pluto. Surface pressure of the atmosphere of Pluto, measured by New Horizons in 2015, is about 1 Pa, temperature on the surface is 40 to 60 K, but it quickly grows with altitude due to methane-generated greenhouse effect. Near the altitude 30 km it reaches 110 K, and then slowly decreases, Pluto is the only trans-Neptunian object with a known atmosphere. Its closest analog is the atmosphere of Triton, although in some aspects it resembles even the atmosphere of Mars, the atmosphere of Pluto has been studied since the 1980s by way of earth-based observation of occultations of stars by Pluto and spectroscopy. In 2015, it was studied from a distance by the spacecraft New Horizons. The main component of the atmosphere of Pluto is nitrogen, content of methane, according to measurements by New Horizons, is 0. 25%. For carbon monoxide, the Earth-based estimates are 0. 025–0. 15% and 0. 05–0. 075%, under influence of high-energy cosmic radiation, these gases react to form more complex compounds, including ethane, ethylene, acetylene, heavier hydrocarbons and nitriles and hydrogen cyanide. These compounds slowly precipitate on the surface, probably, they also include tholins, which are responsible for the brown color of Pluto. The most volatile compound of the atmosphere of Pluto is nitrogen, the second is carbon monoxide, the indicator of volatility is saturated vapor pressure. At temperature 40 K it is about 10 Pa for nitrogen,1 Pa for carbon monoxide and 0.001 Pa for methane and it quickly increases with temperature, and at 60 K approaches to 10000 Pa,3000 Pa and 10 Pa respectively. For heavier-than-methane hydrocarbons, water, ammonia, carbon dioxide and hydrogen cyanide, this pressure remains negligibly low, but actually concentration of, at least, methane, does not depends noticeably of height, longitude and time. But temperature dependence of volatility of methane and nitrogen suggest that concentration of methane will decrease during moving of Pluto further from the Sun, reasons of this discrepancy are unknown. It can be due to existence of separate patches of relatively clean methane ice, seasonal and orbital changes of insolation results in migration of surface ices, they sublimate in some places and condensate in another. According to some estimates, it gives meter-sized changes of their thickness and this results in appreciable changes of brightness and color of Pluto. Methane and carbon monoxide, despite their low abundance, are significant for thermal structure of the atmosphere, methane is a strong heating agent and carbon monoxide is a cooling one
15.
Geology of Pluto
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The geology of Pluto consists of the characteristics of the surface, crust, and interior of Pluto. Because of Plutos distance from Earth, in-depth study from Earth is difficult, because of this, many details about Pluto remained unknown until 14 July 2015, when New Horizons flew through the Pluto system and began transmitting data back to Earth. Plutos surface is composed of more than 98 percent nitrogen ice, with traces of methane, the face of Pluto oriented toward Charon contains more methane ice, whereas the opposite face contains more nitrogen and carbon monoxide ice. Distribution of volatile ices is thought to be season-dependent and influenced more by solar insolation, Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturns moon Iapetus. The color varies between black, dark orange and white. Plutos color is similar to that of Io with slightly more orange. Plutos surface color has changed between 1994 and 2003, the polar region has brightened and the southern hemisphere has darkened. Plutos overall redness has also increased substantially between 2000 and 2002 and these rapid changes are probably related to seasonal condensation and sublimation of portions of Plutos atmosphere, amplified by Plutos extreme axial tilt and high orbital eccentricity. Sputnik Planitia appears to be composed of ices more volatile, softer and more dense than the bedrock of Pluto, including nitrogen, carbon monoxide. A polygonal convection cell structure is visible much of the planitia. No craters have been found, indicating that its surface must be less than 10 million years old, a number of mechanisms are proposed to explain the absence of craters including cryovolcanism, convective overturn, and viscous relaxation - processes that would erase negative topography. Glaciers of what is probably nitrogen ice can be seen flowing from the planitia into adjacent depressions, glaciers appear to be flowing back into the planitia through valleys from these eastern highlands. Mountains several kilometres high have been found along the southwestern and southern edges of Sputnik Planitia, water ice is the only ice detected on Pluto that is strong enough at Plutonian temperatures to support such heights. Cthulhu Regio and other areas have many craters and signatures of methane ice. The dark red color is thought to be due to falling out of Plutos atmosphere. The mid-northern latitudes display a variety of terrain reminiscent of the surface of Triton, a polar cap consisting of methane ice diluted in a thick, transparent slab of nitrogen ice is somewhat darker and redder. These icy ridges were identified as penitentes in a January 2017 Nature paper by Dr. John Moores, penitentes are icy depressions formed by erosion and surrounded by tall spires. Pluto is the planetary body other than Earth on which penitentes have been identified
16.
Moons of Pluto
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The dwarf planet Pluto has five moons down to a detection limit of about 1 km in diameter. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, Charon, the largest of the five moons, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet. The innermost and largest moon, Charon, was discovered by James Christy on 22 June 1978 and this led to a substantial revision in estimates of Plutos size, which had previously assumed that the observed mass and reflected light of the system were all attributable to Pluto alone. The International Astronomical Union officially named these moons Nix and Hydra, Styx, announced on 7 July 2012, was discovered while looking for potential hazards for New Horizons. Charon is about half the diameter of Pluto and is so massive that the barycenter lies between them, approximately 960 km above Plutos surface. Charon and Pluto are also locked, so that they always present the same face toward each other. The IAU General Assembly in August 2006 considered a proposal that Pluto and Charon be reclassified as a double planet, but the proposal was abandoned. Plutos four small moons orbit Pluto at two to four times the distance of Charon, ranging from Styx at 42,700 kilometres to Hydra at 64,800 kilometres from the barycenter of the system and they have nearly circular prograde orbits in the same orbital plane as Charon. All are much smaller than Charon, Nix and Hydra, the two larger, are roughly 42 and 55 kilometers on their longest axis respectively, and Styx and Kerberos are 7 and 12 kilometers respectively. The Pluto system is compact and largely empty. Moons could potentially orbit Pluto at up to 53% of the Hill radius, for example, Psamathe orbits Neptune at 40% of the Hill radius. An intense search conducted by New Horizons confirmed that no larger than 4.5 km in diameter exist at the distances up to 180,000 km from Pluto. Further information is expected as more data from the New Horizons flyby is sent back to Earth. The orbits of the moons are confirmed to be circular and coplanar, with inclinations differing less than 0. 4°, as seen from Earth, these circular orbits appear foreshortened into ellipses depending on Plutos position. The discovery of Nix and Hydra suggested that Pluto could have a ring system, small-body impacts can create debris that can form into a ring system. However, data from a survey by the Advanced Camera for Surveys on the Hubble Space Telescope, by occultation studies. Styx, Nix, and Hydra are thought to be in a 3-body orbital resonance with orbital periods in a ratio of 18,22,33, the ratios should be exact when orbital precession is taken into account. This means that in a recurring cycle there are 11 orbits of Styx for every 9 of Nix and 6 of Hydra, putting Nix and Hydra into a simple 2,3 resonance
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Charon (moon)
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Charon, also known as Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It was discovered in 1978 at the United States Naval Observatory in Washington, with half the diameter and one eighth the mass of Pluto, it is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Pluto–Charon system lies outside Pluto, the New Horizons spacecraft is the only probe that has visited the Pluto system. It approached Charon to within 27,000 km, Charon was discovered by United States Naval Observatory astronomer James Christy, using the 1. 55-meter Flagstaff telescope two months prior. Christy noticed that a slight elongation appeared periodically, later, the bulge was confirmed on plates dating back to April 29,1965. Subsequent observations of Pluto determined that the bulge was due to an accompanying body. The periodicity of the bulge corresponded to Plutos rotation period, which was known from Plutos light curve. This indicated a synchronous orbit, which suggested that the bulge effect was real. Doubts about Charons existence were erased when it and Pluto entered a period of mutual eclipses. This occurs when the Pluto–Charon orbital plane is edge-on as seen from Earth and it was fortuitous that one of these intervals happened to occur soon after Charons discovery. Charon was originally known by the temporary designation S/1978 P1, on June 24,1978, Christy first suggested the name Charon as a scientific-sounding version of his wife Charlenes nickname, Char. The IAU officially adopted the name in late 1985 and it was announced on January 3,1986, there is minor debate over the preferred pronunciation of the name. These indicate only one pronunciation of Charon when referring specifically to Plutos moon, speakers of many languages other than English, and many English-speaking astronomers as well, follow this pronunciation. However, Christy himself pronounced the ch as sh, after his wife Charlene, simulation work published in 2005 by Robin Canup suggested that Charon could have been formed by a collision around 4.5 billion years ago, much like Earth and the Moon. In this model, a large Kuiper belt object struck Pluto at high velocity, destroying itself and blasting off much of Plutos outer mantle, however, such an impact should result in an icier Charon and rockier Pluto than scientists have found. It is now thought that Pluto and Charon might have been two bodies that collided before going into orbit about each other, the collision would have been violent enough to boil off volatile ices like methane but not violent enough to have destroyed either body. The very similar density of Pluto and Charon implies that the parent bodies were not fully differentiated when the impact occurred, Charon and Pluto orbit each other every 6.387 days. The two objects are locked to one another, so each keeps the same face towards the other
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Mordor Macula
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Mordor /ˈmɔːrdɔːr/ is a large dark area about 475 km in diameter near the north pole of Charon, Plutos largest moon. It is named after the land in J. R. R. Tolkiens The Lord of the Rings, which it resembles in shape. The name is not official, the team has been using the name informally. It is not currently known what Mordor is and it may be frozen gases captured from Plutos escaping atmosphere, a large impact basin, or both
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Geology of Charon
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The geology of Charon are the characteristics of the surface, crust, and interior of Plutos moon Charon. Charons diameter is 1,208 km —just over half that of Pluto, Charon is sufficiently massive to have collapsed into a spheroid under its own gravity. Mutual eclipses of Pluto and Charon in the 1980s allowed astronomers to take spectra of Pluto, by subtracting Plutos spectrum from the total, astronomers were able to spectroscopically determine the surface composition of Charon. The northern regions of Charon are composed partially of hydrocarbons and tholins, unlike Plutos surface, which is composed of nitrogen and methane ices, Charons surface appears to be dominated by the less volatile water ice. In 2007, observations by the Gemini Observatory of patches of ammonia hydrates, mutual eclipses of Pluto and Charon in the 1980s allowed astronomers to take spectra of Pluto and then the combined spectrum of the pair. By subtracting Plutos spectrum from the total, astronomers were able to determine the surface composition of Charon. The northern regions of Charon are composed partially of hydrocarbons and tholins, Charon also appears to have little, if any, atmosphere. Photometric mapping of Charons surface shows a trend in albedo, with a bright equator band. The south polar region is darker than the north. The north polar region is dominated by a large dark area informally dubbed Mordor by the New Horizons team. The Mordor Macula is distinctly red, aside from Mordor, however, New Horizons imaged unexpectedly few other impact craters on Charon and found a youthful surface, indicating that Charon is probably geologically active. Charons surface contains several large canyons from 5 to 10 km deep, one system of troughs and cliffs extends for 1050 km. One such graben is Serenity Chasma which is 60 km wide, others include Macross Chasma which lined up with Serenity Chasma forms a belt which extends 1050 km, also Tardis Chasma, Nostromo Chasma, and Argo Chasma which is 5 km deep. Charons north polar region is darker and more reddish than the rest of its surface. The favored explanation for this phenomenon is that they are formed by condensation of gases that escaped from Plutos atmosphere, over millions of years, the residual tholin builds up thick layers, obscuring the icy crust. The south polar region is dark, and was imaged by New Horizons using light reflected off Pluto. Charons volume and mass allow calculation of its density,1. 70±0.02 g/cm3 and this difference is not as large as those of many other collisional satellites. The fact that the ice was still in crystalline form suggested it had been deposited recently, because solar radiation would have degraded it to an amorphous state after roughly 30,000 years
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Styx (moon)
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Styx is a small natural satellite of Pluto whose discovery was announced on 11 July 2012. It was imaged along with Pluto and Plutos other moons by the New Horizons spacecraft in July 2015, Styx is the second satellite of Pluto by distance and the fifth discovered. It was discovered one year after Kerberos, Styx is approximately 13 ×8 km across, and its orbital period is 20.2 days. Styx was discovered by a led by astronomer Mark R. Showalter. The discovery was announced on 11 July 2012, Styx is about half as bright as the dimmest previously known object in the system, Kerberos, and about one hundred thousandth as bright as Pluto. It was designated S/20121, and informally referred to as P5, the survey work leading to the discovery of Styx was in preparation for the mission of the unmanned New Horizons spaceprobe, which flew by the Pluto system on 14 July 2015. However, the New Horizons probe did not detect any smaller moons or rings, the unexpectedly complex moon system around Pluto may be the result of a collision between Pluto and another sizable Kuiper belt object in the distant past. Plutos moons may have coalesced from the debris from such an event, the orbital resonances may have acted as ruts to gather material from the smashup. Styx was originally estimated to have a diameter of between 10 and 25 kilometers and these figures were inferred from the apparent magnitude of Styx and by using an estimated albedo of 0.35 and 0.04 for the lower and upper bounds, respectively. After measurements made by New Horizons, it out that Styx is very irregularly shaped. This process is expected to have created a body consisting mainly of water ice, Styx orbits the Pluto–Charon barycenter at a distance of 42,656 km, putting it between the orbits of Charon and Nix. All of Plutos moons appear to travel in orbits that are nearly circular and coplanar. It is in an 11,6 orbital resonance with Hydra, as a result of this Laplace-like 3-body resonance, it has conjunctions with Nix and Hydra in a 2,5 ratio. Its orbital period of 20.16155 days is about 5. 0% from a 1,3 mean-motion resonance with the Charon–Pluto orbital period of 6.387 days. With the other moons Nix, Kerberos and Hydra, it part of an unusual 1,3,4,5,6 sequence of near resonances. In contrast to its orbit, Styxs rotation is chaotic, like the other small Plutonian moons, Styxs rotation is not tidally locked. Upon discovery, Styx received the minor planet designation S/20121 because it was the first satellite discovered orbiting minor planet in 2012 and it is known informally as P5, meaning the fifth Plutonian moon to be discovered. The convention for naming Plutonian moons is to use names associated with the god Pluto in classical mythology, the public could choose from a selection of Greek mythological names related to the god Pluto, or could propose their own names
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Nix (moon)
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Nix is a natural satellite of Pluto. It was discovered along with Hydra in June 2005 and it was imaged along with Pluto and its other moons by the New Horizons spacecraft as it flew by the Pluto system in July 2015. Of the four small Plutonian moons the best pictures are of Nix, the discovery images were taken on 15 May 2005 and 18 May 2005. Nix and Hydra were independently discovered by Max J. Mutchler on 15 June 2005, the discoveries were announced on 31 October 2005, after confirmation by precoveries from 2002. They were provisionally designated S/2005 P1 and S/2005 P2 and casually referred to as P1 and P2, respectively. The formal name Nix, from the Greek goddess of darkness and night and mother of Charon, was announced on 21 June 2006 on IAU Circular 8723, the initials N and H, for Nix and Hydra, come from New Horizons. The original proposal was to use the classical spelling Nyx, but to avoid confusion with the asteroid 3908 Nyx, jürgen Blunck explains it as the Spanish translation of the Greek name. Nix follows an orbit in the same plane as Charon. It is in a 3,2 orbital resonance with Hydra, as a result of this Laplace-like 3-body resonance, it has conjunctions with Styx and Hydra in a 2,3 ratio. Its orbital period of 24.9 days is also close to a 1,4 orbital resonance with Charon, as with Hydra and perhaps the other small Plutonian moons, Nix tumbles chaotically, the moons axial tilt and day length vary greatly over short timescales. The rotation period has increased by 10% since Nix was discovered. Nix has been measured to be 54 by 41 by 36 kilometers in diameter, indicating an elongated shape. In the discovery image, Nix is 6,300 times fainter than Pluto, New Horizons determined that Nix is approximately 32 kilometers across. Early research appeared to show that Nix was reddish like Pluto and unlike the other moons, New Horizons spotted a large region with a distinctive red tint surrounding a large crater, which may explain these conflicting results. Detailed images of the moon have revealed at least 6 impact craters on it, New Horizons is the only spacecraft that has flown through the Pluto system and hence the only one that has explored Nix. Until 13 July 2015, when NASAs Long Range Reconnaissance Imager on board New Horizons determined Nixs size, all, of Plutos smaller satellites, it was the only one clearly imaged. Steffl, A. J. Mutchler, M. J. Weaver, H. A. Stern, New Constraints on Additional Satellites of the Pluto System
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Kerberos (moon)
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Kerberos is a small natural satellite of Pluto, about 12 km in its longest dimension. It was the moon of Pluto to be discovered and its existence was announced on 20 July 2011. It was imaged, along with Pluto and its four other moons, the first image of Kerberos was released to the public on 22 October 2015. Further observations were made on 3 and 18 July 2011 and Kerberos was verified as a new moon on 20 July 2011 and it was later precovered in images from 15 February 2006 and 25 June 2010. Kerbeross brightness is only about 10% of that of Nix, and it was found because the discovery team took 8-minute exposures. The provisional designation of the satellite varied based on the source used, the International Astronomical Union announced it as S/20111, whereas the New Horizons mission website announced it as S/2011 P1. Upon discovery, Kerberos received the minor planet designation S/20111 because it was the first satellite discovered orbiting minor planet in 2011 and it was initially called P4, meaning the fourth Plutonian moon to be discovered. The convention for naming Plutonian moons is to use names associated with the god Pluto in classical mythology, the public could choose from a selection of Greek mythological names related to the god Pluto, or could propose their own names. After the initial announcement, William Shatner, the actor who played Captain James T, the winning names were submitted to the International Astronomical Union. Cerberus is already the name of an asteroid,1865 Cerberus, on 2 July 2013, the IAU announced that it formally approved the names Kerberos for P4 and Styx for P5. Kerberos has a shape and is approximately 7.4 mi across in its long dimension and 2.8 mi in its shortest dimension. Kerberos has a similar to the other three small moons. Until the New Horizons flyby it was thought that Kerberos was larger and darker, like the other small Plutonian satellites, Kerberos is not tidally locked, its current rotational period is about 5.33 days, although this varies quickly over geological timescales. Observations indicate a circular, equatorial orbit with a radius of approximately 58,000 km, Kerberos orbits between Nix and Hydra and makes a complete orbit around Pluto roughly every 32.1 days. This period is close to a 1,5 orbital resonance with Charon, the New Horizons spacecraft took images of Kerberos during its flyby of the Pluto system on 14 July 2015. Three months later, on 22 October, the first image of the moon was published and it is the last moon to have its picture released
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Hydra (moon)
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Hydra is the outermost known moon of Pluto. It was discovered along with Nix in June 2005, and was visited along with Pluto by New Horizons in July 2015, Hydras surface is probably covered with water ice. Observed within Hydras bright regions is a circular structure with a diameter of approximately 10 kilometers. Hydras reflectivity is intermediate between those of Pluto and Charon, the discovery images were taken on 15 May 2005, and 18 May 2005, Nix and Hydra were independently discovered by Max J. Mutchler on 15 June 2005, and Andrew J. Steffl on 15 August 2005. The discoveries were announced on 31 October 2005, after confirmation by precoveries from 2002 and they were provisionally designated S/2005 P1 and S/2005 P2. The name Hydra was announced on 21 June 2006, in IAU Circular 8723, the name is that of the Hydra, the nine-headed serpent that battled Heracles in Greek mythology. Hydra orbits the barycenter of the system in the plane as Charon and Nix. Its eccentricity of 0.0059 is small, but significantly non-zero, Hydra is in a 2,3 orbital resonance with Nix, and a 6,11 resonance with Styx. As a result of this Laplace-like 3-body resonance, it has conjunctions with Styx and its orbital period of 38.2 days is also close to a 1,6 orbital resonance with Charon, with the timing discrepancy being 0. 3%. This is largely due to the fluctuation of the Pluto–Charon gravitational field. Hydras current rotational period is a mere 10 hours, Hydra is irregular in shape,55 by 40 kilometers in cross-section from one side. It is spectrally neutral like Charon and most of Nix and is composed primarily of water ice, the only detailed photographs of Hydra were taken by the New Horizons spacecraft from approximately 640,000 kilometres away during its flyby of the Pluto–Charon system on 14 July 2015. It also studied Hydras surface composition, reflectivity, and other physical properties. Hydras reflectivity is estimated to be about 45 percent. Sources Steffl, A. J. Mutchler, M. J. Weaver, H. A. Stern, S. A. Durda, D. D. Terrell, D. Merline, W. J. Young, L. A. Young, E. F. Buie, M. W. & Spencer, J. R. New Constraints on Additional Satellites of the Pluto System
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Alan Stern
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Sol Alan Stern is an American engineer and planetary scientist. He is the investigator of the New Horizons mission to Pluto. Stern has been involved in 24 suborbital, orbital, and planetary space missions, one of his projects was the Southwest Ultraviolet Imaging System, an instrument which flew on two space shuttle missions, STS-85 in 1997 and STS-93 in 1999. Stern was Executive Director of the Southwest Research Institutes Space Science and he resigned from that position after nearly a year. In early 2009 Sterns name was mentioned as a contender for the position of NASA administrator under President Obamas administration. Stern has stated, however, that he is not interested in the position at this given his desire to spend time with his family. Stern was born in New Orleans, Louisiana, the son of Joel, marks School of Texas in 1975. He then attended the University of Texas, Austin, where he received his bachelors degrees in physics & astronomy and his masters degrees in aerospace engineering and he earned a doctorate in astrophysics and planetary science from the University of Colorado, Boulder. He received his doctorate in 1989, from 1991 to 1994 he was the leader of Southwest Research Institutes Astrophysical and Planetary Sciences group and was Chair of NASAs Outer Planets Science Working Group. In 1995 he was selected to be a Space Shuttle mission specialist finalist and in 1996 he was a candidate Space Shuttle payload specialist but did not have the opportunity to fly on the Space Shuttle. He has also worked on spacecraft rendezvous theory, terrestrial polar mesospheric clouds, galactic astrophysics, in 2007, Stern was listed among Time Magazines 100 Most Influential People in The World. On August 27,2008 Stern was elected to the Board of Directors of the Challenger Center for Space Science Education, on October 7,2016, Stern was inducted into the Colorado Space Hall of Fame. It was amazing to get to be a part of some first-time exploration like that, within a matter of months, a small group of us had formed a team, an advocacy group, Why dont we get a mission together for Pluto. In December 2008, Stern joined Blue Origin, a company that was founded by Amazon. coms Jeff Bezos as an independent representative for research, the company is located in Kent, Washington and has flight tested some hardware. Stern has extensive experience in instrument development, with a concentration in ultraviolet technologies. Stern is an investigator in NASAs UV sounding rocket program. Stern is also the PI of the ALI CE UV Spectrometer for the ESA/NASA Rosetta comet orbiter and he is the PI of the SWUIS ultraviolet imager, which has flown two Shuttle missions, and the SWUIS-A airborne astronomical facility. In this capacity, Stern has flown numerous WB-57 and F-18 airborne research astronomy missions, Stern and his colleague, Dr. Daniel Durda, have been flying on the modified F/A-18 Hornet with a sophisticated camera system called the Southwest Ultraviolet Imaging System
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Definition of planet
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The definition of planet, since the word was coined by the ancient Greeks, has included within its scope a wide range of celestial bodies. Greek astronomers employed the term asteres planetai, wandering stars, for objects which apparently moved over the sky. Over the millennia, the term has included a variety of different objects, from the Sun and the Moon to satellites and asteroids. By the end of the 19th century the word planet, though it had yet to be defined, had become a term applied only to a small set of objects in the Solar System. After 1992, however, astronomers began to discover many additional objects beyond the orbit of Neptune and these discoveries not only increased the number of potential planets, but also expanded their variety and peculiarity. Some were nearly enough to be stars, while others were smaller than Earths moon. These discoveries challenged long-perceived notions of what a planet could be, the issue of a clear definition for planet came to a head in January 2005 with the discovery of the trans-Neptunian object Eris, a body more massive than the smallest then-accepted planet, Pluto. Under this new definition, Pluto and the other trans-Neptunian objects do not qualify as planets, the IAUs decision has not resolved all controversies, and while many scientists have accepted the definition, some in the astronomical community have rejected it outright. While knowledge of the planets history and is common to most civilizations. The five bodies currently called planets that were known to the Greeks were those visible to the eye, Mercury, Venus, Mars, Jupiter. In his Timaeus, written in roughly 360 BC, Plato mentions, the Sun and Moon and five other stars and his student Aristotle makes a similar distinction in his On the Heavens, The movements of the sun and moon are fewer than those of some of the planets. In his Almagest written in the 2nd century, Ptolemy refers to the Sun, Moon, hyginus explicitly mentions the five stars which many have called wandering, and which the Greeks call Planeta. In his Natural History, written in 77 AD, Pliny the Elder refers to the seven stars, nonnus, the 5th century Greek poet, says in his Dionysiaca, I have oracles of history on seven tablets, and the tablets bear the names of the seven planets. Medieval and Renaissance writers generally accepted the idea of seven planets, indicating that the Sun and the Moon were planets. Even Nicolaus Copernicus, who rejected the model, was ambivalent concerning whether the Sun. And of the five other planets, as the historian of science Thomas Kuhn noted in his book, The Structure of Scientific Revolutions, The Copernicans who denied its traditional title planet to the sun. Were changing the meaning of planet so that it would continue to make distinctions in a world where all celestial bodies. Were seen differently from the way they had seen before
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Double planet
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In astronomy, a double planet is a binary system where both objects are of planetary mass. The term is not recognized by the International Astronomical Union and is not an official classification. In promotional materials advertising the SMART-1 mission and pre-dating the IAU planet definition, some binary asteroids with components of roughly equal mass are sometimes informally referred to as double minor planets. These include binary asteroids 69230 Hermes and 90 Antiope and binary Kuiper belt objects 79360 Sila–Nunam and 1998 WW31, there is debate as to what criteria should be used to distinguish double planet from a planet–moon system. A definition proposed in the Astronomical Journal calls for both bodies to individually satisfy an orbit-clearing criterion in order to be called a double planet, one important consideration in defining double planet is the ratio of the masses of the two bodies. A mass ratio of 1 would indicate bodies of equal mass, using this definition, the satellites of Mars, Jupiter, Saturn, Uranus, and Neptune can all easily be excluded, they all have masses less than 0.00025 of the planets around which they revolve. Some dwarf planets, too, have substantially less massive than the dwarf planets themselves. The most notable exception is the Pluto–Charon system, the Charon-to-Pluto mass ratio of 0.117 is close enough to 1 that Pluto and Charon have frequently been described by many scientists as double dwarf planets. The International Astronomical Union currently calls Charon a satellite of Pluto, the Moon-to-Earth mass ratio of 0.01230 is also notably close to 1 when compared to all other satellite-to-planet ratios. Consequently, some view the Earth-Moon system as a double planet as well. The next criteria both attempt to answer the question How close to 1 must the mass ratio be, currently, the most commonly proposed definition for a double-planet system is one in which the barycenter, around which both bodies orbit, lies outside both bodies. Isaac Asimov suggested a distinction between planet–moon and double-planet structures based in part on what he called a tug-of-war value, which does not consider their relative sizes. This quantity is simply the ratio of the force exerted on the body by the larger body to the force exerted on the smaller body by the Sun. Note that the value does not rely on the mass of the satellite. This formula actually reflects the relation of the effects on the smaller body from the larger body. The tug-of-war figure for Saturns moon Titan is 380, which means that Saturns hold on Titan is 380 times as strong as the Suns hold on Titan. Titans tug-of-war value may be compared with that of Saturns moon Phoebe, so Saturns hold on Phoebe is only 3.5 times as strong as the Suns hold on Phoebe. Asimov calculated tug-of-war values for several satellites of the planets and he showed that even the largest gas giant, Jupiter, had only a slightly better hold than the Sun on its outer captured satellites, some with tug-of-war values not much higher than one
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Dwarf planet
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A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. The International Astronomical Union currently recognizes five dwarf planets, Ceres, Pluto, Haumea, Makemake, another hundred or so known objects in the Solar System are suspected to be dwarf planets. Individual astronomers recognize several of these, and in August 2011 Mike Brown published a list of 390 candidate objects, Stern states that there are more than a dozen known dwarf planets. Only two of these bodies, Ceres and Pluto, have observed in enough detail to demonstrate that they actually fit the IAUs definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto and they subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 are to be named under the assumption that they are dwarf planets. The classification of bodies in other systems with the characteristics of dwarf planets has not been addressed. Starting in 1801, astronomers discovered Ceres and other bodies between Mars and Jupiter which were for some decades considered to be planets. Between then and around 1851, when the number of planets had reached 23, astronomers started using the asteroid for the smaller bodies. With the discovery of Pluto in 1930, most astronomers considered the Solar System to have nine planets and it was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest planet. Although it was more than ten times as massive as the largest object in the asteroid belt, Ceres. In the 1990s, astronomers began to find objects in the region of space as Pluto. Many of these shared several of Plutos key orbital characteristics, and Pluto started being seen as the largest member of a new class of objects and this led some astronomers to stop referring to Pluto as a planet. Several terms, including subplanet and planetoid, started to be used for the now known as dwarf planets. By 2005, three trans-Neptunian objects comparable in size to Pluto had been reported and it became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified. Astronomers were also confident that more objects as large as Pluto would be discovered, Eris was discovered in January 2005, it was thought to be slightly larger than Pluto, and some reports informally referred to it as the tenth planet. As a consequence, the became a matter of intense debate during the IAU General Assembly in August 2006. The IAUs initial draft proposal included Charon, Eris, and Ceres in the list of planets, dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, because they have not cleared their orbits. The IAUs final Resolution 5A preserved this three-category system for the bodies orbiting the Sun
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IAU definition of planet
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A non-satellite body fulfilling only the first two of these criteria is classified as a dwarf planet. According to the IAU, planets and dwarf planets are two classes of objects. A non-satellite body fulfilling only the first criterion is termed a small Solar System body, an alternate proposal included dwarf planets as a subcategory of planets, but IAU members voted against this proposal. The definition was a one, and has drawn both support and criticism from different astronomers, but has remained in use. According to this definition, there are eight planets in the Solar System. The definition distinguishes planets from smaller bodies and is not useful outside the Solar System, extrasolar planets, or exoplanets, are covered separately under a complementary 2003 draft guideline for the definition of planets, which distinguishes them from dwarf stars, which are larger. Before the discoveries of the early 21st century, astronomers had no real need for a definition for planets. With the discovery of Pluto in 1930, astronomers considered the Solar System to have nine planets, along with thousands of bodies such as asteroids. Pluto was thought to be larger than Mercury, in 1978, the discovery of Plutos moon Charon radically changed this picture. By measuring Charons orbital period, astronomers could accurately calculate Plutos mass for the first time, in the 1990s, astronomers began finding other objects at least as far away as Pluto, now known as Kuiper Belt objects, or KBOs. Many of these some of Plutos key orbital characteristics and are now called plutinos. Pluto came to be seen as the largest member of a new class of objects, Plutos eccentric and inclined orbit, while very unusual for a planet in the Solar System, fits in well with the other KBOs. New York Citys newly renovated Hayden Planetarium did not include Pluto in its exhibit of the planets when it reopened as the Rose Center for Earth, astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. They were also concerned about the classification of planets in other planetary systems, in 2006, the matter came to a head with the first measurement of the size of 2003 UB313. That measurement had showed Eris to appear to be larger than Pluto. The process of new discoveries spurring a contentious refinement of Plutos categorization echoed a debate in the 19th century that began with the discovery of Ceres on January 1,1801, astronomers immediately declared the tiny object to be the missing planet between Mars and Jupiter. Within four years, however, the discovery of two objects with comparable sizes and orbits had cast doubt on this new thinking. By 1851, the number of planets had grown to 23, astronomers began cataloguing them separately and began calling them asteroids instead of planets
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