comet

Comet - Wikipedia Comet From Wikipedia, the free encyclopedia This is the latest accepted revision, reviewed on 9 December 2018. Jump to navigation Jump to search This article is about the astronomical objects. For other uses, see Comet (disambiguation). .thumbinner{width:100%!important;max-width:none!important}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:none!important;width:100%!important;text-align:center}}]]>Comets – nucleus, coma and tail: Top: 9P/Tempel (impactor collision: Deep Impact), and 67P/Churyumov–Gerasimenko (Rosetta) Middle: 17P/Holmes and its blue ionized tail, and 81P/Wild (Wild 2) visited by Stardust Bottom: Hale–Bopp seen from Earth in 1997, and C/2011 W3 (Lovejoy) imaged from Earth orbit A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times the Earth's diameter, while the tail may stretch one astronomical unit. If sufficiently bright, a comet may be seen from the Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.[1] Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition. Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids.[2] Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System.[3][4] The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. As of July 2018[update] there are 6,339 known comets,[5] a number that is steadily increasing as they are discovered. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is estimated to be one trillion.[6][7] Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular.[8] Particularly bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first ever to land a robotic spacecraft on a comet,[9] and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior. Contents 1 Etymology 2 Physical characteristics 2.1 Nucleus 2.2 Coma 2.3 Bow shock 2.4 Tails 2.5 Jets 3 Orbital characteristics 3.1 Short period 3.2 Long period 3.3 Oort cloud and Hills cloud 3.4 Exocomets 4 Effects of comets 4.1 Connection to meteor showers 4.2 Comets and impact on life 4.3 Fear of comets 5 Fate of comets 5.1 Departure (ejection) from Solar System 5.2 Volatiles exhausted 5.3 Breakup and collisions 6 Nomenclature 7 History of study 7.1 Early observations and thought 7.2 Orbital studies 7.3 Studies of physical characteristics 7.4 Spacecraft missions 7.5 Great comets 7.6 Sungrazing comets 7.7 Unusual comets 7.8 Centaurs 8 Observation 8.1 Lost 9 In popular culture 10 Gallery 11 See also 12 References 12.1 Bibliography 13 Further reading 14 External links Etymology[edit] A comet was mentioned in the Anglo-Saxon Chronicle that allegedly made an appearance in 729 AD. The word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a latinisation of the Greek κομήτης ("wearing long hair"), and the Oxford English Dictionary notes that the term (ἀστὴρ) κομήτης already meant "long-haired star, comet" in Greek. Κομήτης was derived from κομᾶν ("to wear the hair long"), which was itself derived from κόμη ("the hair of the head") and was used to mean "the tail of a comet".[10][11]The astronomical symbol for comets is ☄ (in Unicode U+2604), consisting of a small disc with three hairlike extensions.[12] Physical characteristics[edit] Nucleus[edit] Main article: Comet nucleus Nucleus of 103P/Hartley as imaged during a spacecraft flyby. The nucleus is about 2 km in length. Comet 81P/Wild exhibits jets on light side and dark side, stark relief, and is dry. The solid, core structure of a comet is known as the nucleus. Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia.[13] As such, they are popularly described as "dirty snowballs" after Fred Whipple's model.[14] However, some comets may have a higher dust content, leading them to be called "icy dirtballs".[15] Research conducted in 2014 suggests that comets are like "deep fried ice cream", in that their surfaces are formed of dense crystalline ice mixed with organic compounds, while the interior ice is colder and less dense.[16] Comet Borrelly exhibits jets, but has no surface ice. The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. In addition to the gases already mentioned, the nuclei contain a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane and perhaps more complex molecules such as long-chain hydrocarbons and amino acids.[17][18] In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission.[19] In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine, and related organic molecules) may have been formed on asteroids and comets.[20][21]The outer surfaces of cometary nuclei have a very low albedo, making them among the least reflective objects found in the Solar System. The Giotto space probe found that the nucleus of Halley's Comet reflects about four percent of the light that falls on it,[22] and Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%;[22] by comparison, asphalt reflects seven percent. The dark surface material of the nucleus may consist of complex organic compounds. Solar heating drives off lighter volatile compounds, leaving behind larger organic compounds that tend to be very dark, like tar or crude oil. The low reflectivity of cometary surfaces causes them to absorb the heat that drives their outgassing processes.[23]Comet nuclei with radii of up to 30 kilometres (19 mi) have been observed,[24] but ascertaining their exact size is difficult.[25] The nucleus of 322P/SOHO is probably only 100–200 metres (330–660 ft) in diameter.[26] A lack of smaller comets being detected despite the increased sensitivity of instruments has led some to suggest that there is a real lack of comets smaller than 100 metres (330 ft) across.[27] Known comets have been estimated to have an average density of 0.6 g/cm3 (0.35 oz/cu in).[28] Because of their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes.[29]Roughly six percent of the near-Earth asteroids are thought to be extinct nuclei of comets that no longer experience outgassing,[30] including 14827 Hypnos and 3552 Don Quixote. Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals.[31][32] Further, the ALICE spectrograph on Rosetta determined that electrons (within 1 km (0.62 mi) above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma.[33][34] Instruments on the Philae lander found at least sixteen organic compounds at the comet's surface, four of which (acetamide, acetone, methyl isocyanate and propionaldehyde) have been detected for the first time on a comet.[35][36][37] Properties of some comets Name Dimensions(km) Density(g/cm3) Mass(kg)[38] Refs Halley's Comet 15 × 8 × 8 0.6 3×1014 [39][40]Tempel 1 7.6 × 4.9 0.62 7.9×1013 [28][41]19P/Borrelly 8 × 4 × 4 0.3 2.0×1013 [28]81P/Wild 5.5 × 4.0 × 3.3 0.6 2.3×1013 [28][42]67P/Churyumov–Gerasimenko 4.1 × 3.3 × 1.8 0.47 1.0×1013 [43][44]Coma[edit] Main article: Coma (cometary) Hubble image of Comet ISON shortly before perihelion.[45] The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the "coma". The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous "tail" to form pointing away from the Sun.[46]The coma is generally made of  H2O and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun.[47] The  H2O parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization, with the solar wind playing a minor role in the destruction of water compared to photochemistry.[47] Larger dust particles are left along the comet's orbital path whereas smaller particles are pushed away from the Sun into the comet's tail by light pressure.[48] C/2006 W3 (Chistensen) emitting carbon gas (IR image) Although the solid nucleus of comets is generally less than 60 kilometres (37 mi) across, the coma may be thousands or millions of kilometres across, sometimes becoming larger than the Sun.[49] For example, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun.[50] The Great Comet of 1811 also had a coma roughly the diameter of the Sun.[51] Even though the coma can become quite large, its size can decrease about the time it crosses the orbit of Mars around 1.5 astronomical units (220,000,000 km; 140,000,000 mi) from the Sun.[51] At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, and in doing so enlarging the tail.[51] Ion tails have been observed to extend one astronomical unit (150 million km) or more.[50]Both the coma and tail are illuminated by the Sun and may become visible when a comet passes through the inner Solar System, the dust reflects sunlight directly while the gases glow from ionisation.[52] Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye.[53] Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma greatly increases for a period of time. This happened in 2007 to Comet Holmes.[54]In 1996, comets were found to emit X-rays.[55] This greatly surprised astronomers because X-ray emission is usually associated with very high-temperature bodies. The X-rays are generated by the interaction between comets and the solar wind: when highly charged solar wind ions fly through a cometary atmosphere, they collide with cometary atoms and molecules, "stealing" one or more electrons from the atom in a process called "charge exchange". This exchange or transfer of an electron to the solar wind ion is followed by its de-excitation into the ground state of the ion by the emission of X-rays and far ultraviolet photons.[56] Bow shock[edit] Bow shocks form at as a result of the interaction between the solar wind and the cometary ionosphere, which is created by ionization of gases in the coma. As the comet approaches the Sun, increasing outgassing rates cause the coma to expand, and the sunlight ionizes gases in the coma. When the solar wind passes through this ion coma, the bow shock appears. The first observations were made in the 1980s and 90s as several spacecraft flew by comets 21P/Giacobini–Zinner,[57]1P/Halley,[58] and 26P/Grigg–Skjellerup.[59] It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at, for example, Earth. These observations were all made near perihelion when the bow shocks already were fully developed. The Rosetta spacecraft observed the bow shock at comet 67P/Churyumov–Gerasimenko at an early stage of bow shock development when the outgassing increased during the comet's journey toward the Sun. This young bow shock was called the "infant bow shock". The infant bow shock is asymmetric and, relative to the distance to the nucleus, wider than fully developed bow shocks.[60] Tails[edit] Main article: Comet tail Diagram of a comet showing the dust trail (or antitail), the dust tail, and the ion gas tail, which is formed by the solar wind flow. In the outer Solar System, comets remain frozen and inactive and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from observations by the Hubble Space Telescope[61][62] but these detections have been questioned.[63][64] As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. Typical direction of tails over a comet's orbit near the Sun The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail called the type II or dust tail.[52] At the same time, the ion or type I tail, made of gases, always points directly away from the Sun because this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory.[65] On occasions - such as when the Earth passes through a comet's orbital plane, a tail pointing in the opposite direction to the ion and dust tails called the antitail may be seen.[66]The observation of antitails contributed significantly to the discovery of solar wind.[67] The ion tail is formed as a result of the ionisation by solar ultra-violet radiation of particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge, which in turn gives rise to an "induced magnetosphere" around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. Because the relative orbital speed of the comet and the solar wind is supersonic, a bow shock is formed upstream of the comet in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the solar magnetic field with plasma, such that the field lines "drape" around the comet forming the ion tail.[68]If the ion tail loading is sufficient, the magnetic field lines are squeezed together to the point where, at some distance along the ion tail, magnetic reconnection occurs. This leads to a "tail disconnection event".[68] This has been observed on a number of occasions, one notable event being recorded on 20 April 2007, when the ion tail of Encke's Comet was completely severed while the comet passed through a coronal mass ejection. This event was observed by the STEREO space probe.[69]In 2013, ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to the ion tail seen streaming from a comet under similar conditions."[70][71] Jets[edit] Gas and snow jets of 103P/Hartley Uneven heating can cause newly generated gases to break out of a weak spot on the surface of comet's nucleus, like a geyser.[72] These streams of gas and dust can cause the nucleus to spin, and even split apart.[72] In 2010 it was revealed dry ice (frozen carbon dioxide) can power jets of material flowing out of a comet nucleus.[73] Infrared imaging of Hartley 2 shows such jets exiting and carrying with it dust grains into the coma.[74] Orbital characteristics[edit] Most comets are small Solar System bodies with elongated elliptical orbits that take them close to the Sun for a part of their orbit and then out into the further reaches of the Solar System for the remainder.[75] Comets are often classified according to the length of their orbital periods: The longer the period the more elongated the ellipse. Short period[edit] Main articles: List of numbered comets and List of Halley-type comets Periodic comets or short-period comets are generally defined as those having orbital periods of less than 200 years.[76] They usually orbit more-or-less in the ecliptic plane in the same direction as the planets.[77] Their orbits typically take them out to the region of the outer planets (Jupiter and beyond) at aphelion; for example, the aphelion of Halley's Comet is a little beyond the orbit of Neptune. Comets whose aphelia are near a major planet's orbit are called its "family".[78] Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits.[79]At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet. Short-period comets with orbital periods less than 20 years and low inclinations (up to 30 degrees) to the ecliptic are called traditional Jupiter-family comets (JFCs).[80][81] Those like Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets (HTCs).[82][83] As of 2018[update], only 82 HTCs have been observed,[84] compared with 659 identified JFCs.[85]Recently discovered main-belt comets form a distinct class, orbiting in more circular orbits within the asteroid belt.[86]Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further gravitational perturbations.[87] Short-period comets have a tendency for their aphelia to coincide with a giant planet's semi-major axis, with the JFCs being the largest group.[81] It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by the gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined. These perturbations can deflect long-period comets into shorter orbital periods.[88][89]Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/scattered disc[90] —a disk of objects in the trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesised its existence).[91] Vast swarms of comet-like bodies are thought to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper belt objects) or nearby stars (in the case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards toward the Sun to form a visible comet. Unlike the return of periodic comets, whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable.[92] Long period[edit] See also: List of long-period comets, List of near-parabolic comets, and List of hyperbolic comets Orbits of Comet Kohoutek (red) and the Earth (blue), illustrating the high eccentricity of its orbit and its rapid motion when close to the Sun. Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands of years.[93] An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System.[94] For example, Comet McNaught had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage epoch in January 2007 but is bound to the Sun with roughly a 92,600-year orbit because the eccentricity drops below 1 as it moves farther from the Sun. The future orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. By definition long-period comets remain gravitationally bound to the Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as Comet West and C/1999 F1 can have aphelion distances of nearly 70,000 AU with orbital periods estimated around 6 million years. Single-apparition or non-periodic comets are similar to long-period comets because they also have parabolic or slightly hyperbolic trajectories[93] when near perihelion in the inner Solar System. However, gravitational perturbations from giant planets cause their orbits to change. Single-apparition comets have a hyperbolic or parabolic osculating orbit which allows them to permanently exit the Solar System after a single pass of the Sun.[95] The Sun's Hill sphere has an unstable maximum boundary of 230,000 AU (1.1 parsecs (3.6 light-years)).[96] Only a few hundred comets have been seen to reach a hyperbolic orbit (e > 1) when near perihelion[97] that using a heliocentric unperturbed two-body best-fit suggests they may escape the Solar System. As of 2018, 1I/ʻOumuamua is the only object with an eccentricity significantly greater than one that has been detected, indicating an origin outside the Solar System. While ʻOumuamua showed no optical signs of cometary activity during its passage through the inner Solar System in October 2017, changes to its trajectory—which suggests outgassing—indicate that it is indeed a comet.[98] Comet C/1980 E1 had an orbital period of roughly 7.1 million years before the 1982 perihelion passage, but a 1980 encounter with Jupiter accelerated the comet giving it the largest eccentricity (1.057) of any known hyperbolic comet.[99] Comets not expected to return to the inner Solar System include C/1980 E1, C/2000 U5, C/2001 Q4 (NEAT), C/2009 R1, C/1956 R1, and C/2007 F1 (LONEOS). Some authorities use the term "periodic comet" to refer to any comet with a periodic orbit (that is, all short-period comets plus all long-period comets),[100] whereas others use it to mean exclusively short-period comets.[93] Similarly, although the literal meaning of "non-periodic comet" is the same as "single-apparition comet", some use it to mean all comets that are not "periodic" in the second sense (that is, to also include all comets with a period greater than 200 years). Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. If comets pervaded interstellar space, they would be moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). If such objects entered the Solar System, they would have positive specific orbital energy and would be observed to have genuinely hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century within Jupiter's orbit, give or take one and perhaps two orders of magnitude.[101] Hyperbolic comet discoveries[102] Year 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 Number 12 7 8 4 13 10 16 9 16 5 18 3 Oort cloud and Hills cloud[edit] Main article: Oort cloud The Oort cloud thought to surround the Solar System The Oort cloud is thought to occupy a vast space starting from between 2,000 and 5,000 AU (0.03 and 0.08 ly)[103] to as far as 50,000 AU (0.79 ly)[82] from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 AU (1.58 and 3.16 ly).[103] The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 AU (0.32–0.79 ly), and a doughnut-shaped inner cloud, the Hills cloud, of 2,000–20,000 AU (0.03–0.32 ly).[104] The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets that fall to inside the orbit of Neptune.[82] The inner Oort cloud is also known as the Hills cloud, named after J. G. Hills, who proposed its existence in 1981.[105] Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo;[105][106][107] it is seen as a possible source of new comets that resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years.[108] Exocomets[edit] Main article: Exocomet Exocomets beyond the Solar System have also been detected and may be common in the Milky Way.[109] The first exocomet system detected was around Beta Pictoris, a very young A-type main-sequence star, in 1987.[110][111] A total of 10 such exocomet systems have been identified as of 2013[update], using the absorption spectrum caused by the large clouds of gas emitted by comets when passing close to their star.[109][110] Effects of comets[edit] Connection to meteor showers[edit] Diagram of Perseids meteors As a result of outgassing, comets leave in their wake a trail of solid debris too large to be swept away by radiation pressure and the solar wind.[112] If the Earth's orbit sends it through that debris, there are likely to be meteor showers as Earth passes through. The Perseid meteor shower, for example, occurs every year between 9 and 13 August, when Earth passes through the orbit of Comet Swift–Tuttle.[113]Halley's Comet is the source of the Orionid shower in October.[113] Comets and impact on life[edit] Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding the young Earth about 4 billion years ago brought the vast quantities of water that now fill the Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea.[114] The detection of organic molecules, including polycyclic aromatic hydrocarbons,[16] in significant quantities in comets has led to speculation that comets or meteorites may have brought the precursors of life—or even life itself—to Earth.[115] In 2013 it was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the amino acids that make up proteins through shock synthesis.[116] In 2015, scientists found significant amounts of molecular oxygen in the outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed.[117]It is suspected that comet impacts have, over long timescales, also delivered significant quantities of water to the Earth's Moon, some of which may have survived as lunar ice.[118] Comet and meteoroid impacts are also thought to be responsible for the existence of tektites and australites.[119] Fear of comets[edit] Fear of comets as acts of God and signs of impending doom was highest in Europe from AD 1200 to 1650.[citation needed] The year after the Great Comet of 1618, for example, Gotthard Arthusius published a pamphlet stating that it was a sign that the Day of Judgment was near.[120] He listed ten pages of comet-related disasters, including "earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices". By 1700 most scholars concluded that such events occurred whether a comet was seen or not. Using Edmund Halley's records of comet sightings, however, William Whiston in 1711 wrote that the Great Comet of 1680 had a periodicity of 574 years and was responsible for the worldwide flood in the Book of Genesis, by pouring water on the Earth. His announcement revived for another century fear of comets, now as direct threats to the world instead of signs of disasters.[121] Spectroscopic analysis in 1910 found the toxic gas cyanogen in the tail of Halley's Comet,[122] causing panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.[123] Fate of comets[edit] Departure (ejection) from Solar System[edit] If a comet is traveling fast enough, it may leave the Solar System. Such comets follow the open path of a hyperbola, and as such they are called hyperbolic comets. To date, comets are only known to be ejected by interacting with another object in the Solar System, such as Jupiter.[124] An example of this is thought to be Comet C/1980 E1, which was shifted from a predicted orbit of 7.1 million years around the Sun, to a hyperbolic trajectory, after a 1980 close pass by the planet Jupiter.[125] Volatiles exhausted[edit] Main article: Extinct comet Jupiter-family comets and long-period comets appear to follow very different fading laws. The JFCs are active over a lifetime of about 10,000 years or ~1,000 orbits whereas long-period comets fade much faster. Only 10% of the long-period comets survive more than 50 passages to small perihelion and only 1% of them survive more than 2,000 passages.[30] Eventually most of the volatile material contained in a comet nucleus evaporates, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid.[126] Some asteroids in elliptical orbits are now identified as extinct comets.[127][128][129][130] Roughly six percent of the near-Earth asteroids are thought to be extinct comet nuclei.[30] Breakup and collisions[edit] The nucleus of some comets may be fragile, a conclusion supported by the observation of comets splitting apart.[131] A significant cometary disruption was that of Comet Shoemaker–Levy 9, which was discovered in 1993. A close encounter in July 1992 had broken it into pieces, and over a period of six days in July 1994, these pieces fell into Jupiter's atmosphere—the first time astronomers had observed a collision between two objects in the Solar System.[132][133] Other splitting comets include 3D/Biela in 1846 and 73P/Schwassmann–Wachmann from 1995 to 2006.[134] Greek historian Ephorus reported that a comet split apart as far back as the winter of 372–373 BC.[135] Comets are suspected of splitting due to thermal stress, internal gas pressure, or impact.[136]Comets 42P/Neujmin and 53P/Van Biesbroeck appear to be fragments of a parent comet. Numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical.[137]Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki. Biela's Comet was one significant example, when it broke into two pieces during its passage through the perihelion in 1846. These two comets were seen separately in 1852, but never again afterward. Instead, spectacular meteor showers were seen in 1872 and 1885 when the comet should have been visible. A minor meteor shower, the Andromedids, occurs annually in November, and it is caused when the Earth crosses the orbit of Biela's Comet.[138]Some comets meet a more spectacular end – either falling into the Sun[139] or smashing into a planet or other body. Collisions between comets and planets or moons were common in the early Solar System: some of the many craters on the Moon, for example, may have been caused by comets. A recent collision of a comet with a planet occurred in July 1994 when Comet Shoemaker–Levy 9 broke up into pieces and collided with Jupiter.[140] Brown spots mark impact sites of Comet Shoemaker–Levy 9 on JupiterThe break up of 73P/Schwassmann–Wachmann within three days (1995)Ghost tail of C/2015 D1 (SOHO) after passage at the sunDisintegration of P/2013 R3 (2014)[141] Nomenclature[edit] Main article: Naming of comets Halley's Comet in 1910 The names given to comets have followed several different conventions over the past two centuries. Prior to the early 20th century, most comets were simply referred to by the year when they appeared, sometimes with additional adjectives for particularly bright comets; thus, the "Great Comet of 1680", the "Great Comet of 1882", and the "Great January Comet of 1910". After Edmund Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759 by calculating its orbit, that comet became known as Halley's Comet.[142] Similarly, the second and third known periodic comets, Encke's Comet[143] and Biela's Comet,[144] were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their appearance.[145]In the early 20th century, the convention of naming comets after their discoverers became common, and this remains so today. A comet can be named after its discoverers, or an instrument or program that helped to find it.[145] History of study[edit] Main article: Observational history of comets Early observations and thought[edit] Halley's Comet appeared in 1066, prior to the Battle of Hastings (Bayeux Tapestry). From ancient sources, such as Chinese oracle bones, it is known that comets have been noticed by humans for millennia.[146] Until the sixteenth century, comets were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants.[147][148]Aristotle believed that comets were atmospheric phenomena, due to the fact that they could appear outside of the Zodiac and vary in brightness over the course of a few days.[149]Pliny the Elder believed that comets were connected with political unrest and death.[150]In India, by the 6th century astronomers believed that comets were celestial bodies that re-appeared periodically. This was the view expressed in the 6th century by the astronomers Varāhamihira and Bhadrabahu, and the 10th-century astronomer Bhaṭṭotpala listed the names and estimated periods of certain comets, but it is not known how these figures were calculated or how accurate they were.[151]In the 16th century Tycho Brahe demonstrated that comets must exist outside the Earth's atmosphere by measuring the parallax of the Great Comet of 1577 from observations collected by geographically separated observers. Within the precision of the measurements, this implied the comet must be at least four times more distant than from the Earth to the Moon.[152][153] Orbital studies[edit] Further information: Observational history of comets § Orbital studies The orbit of the comet of 1680, fitted to a parabola, as shown in Isaac Newton's Principia Isaac Newton, in his Principia Mathematica of 1687, proved that an object moving under the influence of gravity must trace out an orbit shaped like one of the conic sections, and he demonstrated how to fit a comet's path through the sky to a parabolic orbit, using the comet of 1680 as an example.[154]In 1705, Edmond Halley (1656–1742) applied Newton's method to twenty-three cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar orbital elements, and he was further able to account for the slight differences in their orbits in terms of gravitational perturbation caused by Jupiter and Saturn. Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–9.[155] Halley's predicted return date was later refined by a team of three French mathematicians: Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute, who predicted the date of the comet's 1759 perihelion to within one month's accuracy.[156][157] When the comet returned as predicted, it became known as Halley's Comet (with the latter-day designation of 1P/Halley). It will next appear in 2061.[158] Studies of physical characteristics[edit] Further information: Observational history of comets § Studies of physical characteristics From his huge vapouring train perhaps to shakeReviving moisture on the numerous orbs,Thro' which his long ellipsis winds; perhapsTo lend new fuel to declining suns,To light up worlds, and feed th' ethereal fire. James Thomson The Seasons (1730; 1748)[159] Isaac Newton described comets as compact and durable solid bodies moving in oblique orbit and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the Sun. Newton suspected that comets were the origin of the life-supporting component of air.[160]As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, Immanuel Kant hypothesized that comets are composed of some volatile substance, whose vaporization gives rise to their brilliant displays near perihelion.[161] In 1836, the German mathematician Friedrich Wilhelm Bessel, after observing streams of vapor during the appearance of Halley's Comet in 1835, proposed that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit, and he argued that the non-gravitational movements of Encke's Comet resulted from this phenomenon.[162]In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock.[163] This "dirty snowball" model soon became accepted and appeared to be supported by the observations of an armada of spacecraft (including the European Space Agency's Giotto probe and the Soviet Union's Vega 1 and Vega 2) that flew through the coma of Halley's Comet in 1986, photographed the nucleus, and observed jets of evaporating material.[164]On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on the dwarf planet Ceres, the largest object in the asteroid belt.[165] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.[166] The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."[166] On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, H2CO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).[167][168] Spacecraft missions[edit] See also: List of comets visited by spacecraft The Halley Armada describes the collection of spacecraft missions that visited and/or made observations of Halley's Comet 1980s perihelion. Deep Impact. Debate continues about how much ice is in a comet. In 2001, the Deep Space 1 spacecraft obtained high-resolution images of the surface of Comet Borrelly. It was found that the surface of comet Borrelly is hot and dry, with a temperature of between 26 to 71 °C (79 to 160 °F), and extremely dark, suggesting that the ice has been removed by solar heating and maturation, or is hidden by the soot-like material that covers Borrelly.[169] In July 2005, the Deep Impact probe blasted a crater on Comet Tempel 1 to study its interior. The mission yielded results suggesting that the majority of a comet's water ice is below the surface and that these reservoirs feed the jets of vaporised water that form the coma of Tempel 1.[170] Renamed EPOXI, it made a flyby of Comet Hartley 2 on 4 November 2010. Stardust. Data from the Stardust mission show that materials retrieved from the tail of Wild 2 were crystalline and could only have been "born in fire," at extremely high temperatures of over 1,000 °C (1,830 °F).[171][172] Although comets formed in the outer Solar System, radial mixing of material during the early formation of the Solar System is thought to have redistributed material throughout the proto-planetary disk.[173] As a result, comets also contain crystalline grains that formed in the early, hot inner Solar System. This is seen in comet spectra as well as in sample return missions. More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials".[174] These new results have forced scientists to rethink the nature of comets and their distinction from asteroids.[175] Rosetta. The Rosetta probe orbited Comet Churyumov–Gerasimenko. On 12 November 2014, its lander Philae successfully landed on the comet's surface, the first time a spacecraft has ever landed on such an object in history.[176]Great comets[edit] Main article: Great comet Woodcut of the Great Comet of 1577 Approximately once a decade, a comet becomes bright enough to be noticed by a casual observer, leading such comets to be designated as great comets.[135] Predicting whether a comet will become a great comet is notoriously difficult, as many factors may cause a comet's brightness to depart drastically from predictions.[177] Broadly speaking, if a comet has a large and active nucleus, will pass close to the Sun, and is not obscured by the Sun as seen from the Earth when at its brightest, it has a chance of becoming a great comet. However, Comet Kohoutek in 1973 fulfilled all the criteria and was expected to become spectacular but failed to do so.[178]Comet West, which appeared three years later, had much lower expectations but became an extremely impressive comet.[179]The late 20th century saw a lengthy gap without the appearance of any great comets, followed by the arrival of two in quick succession—Comet Hyakutake in 1996, followed by Hale–Bopp, which reached maximum brightness in 1997 having been discovered two years earlier. The first great comet of the 21st century was C/2006 P1 (McNaught), which became visible to naked eye observers in January 2007. It was the brightest in over 40 years.[180] Sungrazing comets[edit] Main article: Sungrazing comet A sungrazing comet is a comet that passes extremely close to the Sun at perihelion, generally within a few million kilometres.[181] Although small sungrazers can be completely evaporated during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong tidal forces they experience often lead to their fragmentation.[182]About 90% of the sungrazers observed with SOHO are members of the Kreutz group, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner Solar System.[183] The remainder contains some sporadic sungrazers, but four other related groups of comets have been identified among them: the Kracht, Kracht 2a, Marsden, and Meyer groups. The Marsden and Kracht groups both appear to be related to Comet 96P/Machholz, which is also the parent of two meteor streams, the Quadrantids and the Arietids.[184] Unusual comets[edit] Euler diagram showing the types of bodies in the Solar System. Of the thousands of known comets, some exhibit unusual properties. Comet Encke (2P/Encke) orbits from outside the asteroid belt to just inside the orbit of the planet Mercury whereas the Comet 29P/Schwassmann–Wachmann currently travels in a nearly circular orbit entirely between the orbits of Jupiter and Saturn.[185]2060 Chiron, whose unstable orbit is between Saturn and Uranus, was originally classified as an asteroid until a faint coma was noticed.[186] Similarly, Comet Shoemaker–Levy 2 was originally designated asteroid 1990 UL3.[187](See also Fate of comets, above) Centaurs[edit] Main article: Centaur (minor planet) Centaurs typically behave with characteristics of both asteroids and comets.[188] Centaurs can be classified as comets such as 60558 Echeclus, and 166P/NEAT. 166P/NEAT was discovered while it exhibited a coma, and so is classified as a comet despite its orbit, and 60558 Echeclus was discovered without a coma but later became active,[189] and was then classified as both a comet and an asteroid (174P/Echeclus). One plan for Cassini involved sending it to a centaur, but NASA decided to destroy it instead.[190] Observation[edit] A comet may be discovered photographically using a wide-field telescope or visually with binoculars. However, even without access to optical equipment, it is still possible for the amateur astronomer to discover a sungrazing comet online by downloading images accumulated by some satellite observatories such as SOHO.[191] SOHO's 2000th comet was discovered by Polish amateur astronomer Michał Kusiak on 26 December 2010[192] and both discoverers of Hale-Bopp used amateur equipment (although Hale was not an amateur). Lost[edit] Main article: Lost comet A number of periodic comets discovered in earlier decades or previous centuries are now lost comets. Their orbits were never known well enough to predict future appearances or the comets have disintegrated. However, occasionally a "new" comet is discovered, and calculation of its orbit shows it to be an old "lost" comet. An example is Comet 11P/Tempel–Swift–LINEAR, discovered in 1869 but unobservable after 1908 because of perturbations by Jupiter. It was not found again until accidentally rediscovered by LINEAR in 2001.[193] There are at least 18 comets that fit this category.[194] In popular culture[edit] See also: Comets in fiction and Category:Impact events in fiction The depiction of comets in popular culture is firmly rooted in the long Western tradition of seeing comets as harbingers of doom and as omens of world-altering change.[195] Halley's Comet alone has caused a slew of sensationalist publications of all sorts at each of its reappearances. It was especially noted that the birth and death of some notable persons coincided with separate appearances of the comet, such as with writers Mark Twain (who correctly speculated that he'd "go out with the comet" in 1910)[195] and Eudora Welty, to whose life Mary Chapin Carpenter dedicated the song "Halley Came to Jackson".[195]In times past, bright comets often inspired panic and hysteria in the general population, being thought of as bad omens. More recently, during the passage of Halley's Comet in 1910, the Earth passed through the comet's tail, and erroneous newspaper reports inspired a fear that cyanogen in the tail might poison millions,[196] whereas the appearance of Comet Hale–Bopp in 1997 triggered the mass suicide of the Heaven's Gate cult.[197]In science fiction, the impact of comets has been depicted as a threat overcome by technology and heroism (as in the 1998 films Deep Impact and Armageddon), or as a trigger of global apocalypse (Lucifer's Hammer, 1979) or zombies (Night of the Comet, 1984).[195] In Jules Verne's Off on a Comet a group of people are stranded on a comet orbiting the Sun, while a large manned space expedition visits Halley's Comet in Sir Arthur C. Clarke's novel 2061: Odyssey Three.[198] Gallery[edit] Comet C/2006 P1 (McNaught) taken from Victoria, Australia 2007 The Great Comet of 1882 is a member of the Kreutz group Great Comet 1861 Comet Hyakutake (X-ray, ROSAT satellite) "Active asteroid" 311P/PANSTARRS with several tails[199] Comet Siding Spring (Hubble; 11 March 2014) Mosaic of 20 comets discovered by the WISE space telescope NEOWISE – first four years of data starting in December 2013 C/2011 W3 (Lovejoy) heads towards the Sun View from the impactor in its last moments before hitting Comet Tempel 1 during the Deep Impact mission Videos Play media NASA is developing a comet harpoon for returning samples to Earth Play media Comet Encke loses its tail See also[edit] Book: Solar System Comet vintages Lists of comets List of impact craters on Earth List of unconfirmed impact craters on Earth The Big SplashReferences[edit] ^ Randall, Lisa (2015). Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe. 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Retrieved 14 August 2013. ^ Sagan & Druyan 1997, p. 14 ^ Sagan & Druyan 1997, p. 24 ^ Sagan & Druyan 1997, pp. 27–28 ^ Kelley, David H.; Milone, Eugene F. (2011). Exploring Ancient Skies: A Survey of Ancient and Cultural Astronomy (2nd ed.). Springer Science+Business Media. p. 293. doi:10.1007/978-1-4419-7624-6. ISBN 978-1-4419-7624-6. OCLC 710113366. ^ "A Brief History of Comets I (until 1950)". European Southern Observatory. Retrieved 14 August 2013. ^ Sagan & Druyan 1997, p. 37 ^ Newton, Isaac (1687). "Lib. 3, Prop. 41". Philosophiæ Naturalis Principia Mathematica. Royal Society of London. ISBN 0-521-07647-1. ^ Halleio, E. (1704). "Astronomiae Cometicae Synopsis, Autore Edmundo Halleio apud Oxonienses. Geometriae Professore Saviliano, & Reg. Soc. S" (PDF). Philosophical Transactions of the Royal Society of London. 24 (289–304): 1882. doi:10.1098/rstl.1704.0064. ^ On 1758 November 14, Alexis Clairaut announced to the Royal Academy of Sciences in Paris his prediction of the date at which Halley's comet would return: Clairaut (January 1759) "Mémoire sur la cométe de 1682," Le Journal des Sçavans, pp. 38–45. On p. 44, Clairaut predicted that Halley's comet would return in mid April 1759. From p. 44: " … il me paroît que la Cométe attendue doit passer à son périhélie vers le milieu du mois d'Avril prochain." ( … it seems to me that the expected comet must pass its perihelion towards the middle of next April.) On p. 40, Clairaut stated that his prediction might be slightly incorrect due to the presence of unknown planets beyond Saturn: "Un corps qui passe dans des régions aussi éloignées, & qui échappe à nos yeux pendant des intervalles aussi longs, pourroit être soumis à des forces totalement inconnues; telles que l'action d'autres Cométes, ou même de quelque planéte toujours trop distante du Soleil pour être jamais apperçue." (A body [i.e., Halley's comet] which passes into regions so remote, and which escapes our eyes during such long intervals, might be subjected to totally unknown forces; such as the action of other comets, or even of some planet always too far from the sun to ever be perceived.) On 1759 April 7, the French astronomer Joseph-Nicolas Delisle announced to the Royal Academy of Sciences in Paris that he and his assistant Charles Messier had observed the return of Halley's comet, as predicted: de l'Isle (June 1759) "Lettre de M. de l'Isle … contenant la découverte du retour de la Comète de 1682, … " (Letter from Mr. de l'Isle … containing the discovery of the return of the comet of 1682), Le Journal des Sçavans, pp. 356–364. De l'Isle subsequently admitted that the comet's return had first been seen by a German amateur astronomer and farmer, Georg Palitzsch: de l'Isle (August 1759) "Seconde lettre de M. de l'Isle," Le Journal des Sçavans, pp. 523–529. From p. 526: " … j'ai reçu une Lettre d'Heidelberg le premier Avril au soir, dans laquelle l'on m'écrit que l'on a publié à Leipsick le 24 Janvier de cette année un Mémoire Allemand dans lequel il est dit que cette Comète a été vue en Saxe par un Paysan, nommé Palisch, le 25 & 26 Décembre de l'année dernière; j'ai bien de la peine à concevoir comment ce Paysan aura pû la découvrir, cette Comète, … " ( … I received a letter from Heidelberg on the first of April in the evening, in which it is written to me that there had been published at Leipzig on the 24th of January of this year a German memoir in which it is said that this comet had been seen in Saxony by a peasant, named Palisch, on the 25th and 26th of December of last year; I can hardly conceive how this peasant could have discovered it, this comet, … ) The story behind the rediscovery of Halley's comet was given by Joseph Lalande in: Delalande, Tables astronomiques de M. Halley, … Et l'Histoire de la Comete de 1759. [Astronomical tables of Mr. Halley, … and the history of the comet of 1759.] (Paris, France: Durand, 1759), pp. 91 ff. Lalande acknowledged the contributions of Madame Lepaute to predicting the return of Halley's comet on p. 110. From p. 110: " … mais il faut convenir que cette suite immense de détails m'eût semblé effrayante, si Madame LEPAUTE, appliquée depuis long-temps & avec succès aux calculs Astronomiques, n'en eût partagé le travail." ( … but it must be admitted that this immense series of details would have seemed frightening to me if Madame LEPAUTE, [who has] long applied [herself] successfully to astronomical calculations, had not shared in the work.) See also: Broughton, Peter (1985) "The first predicted return of comet Halley," Journal for the History of Astronomy, 16 : 123–132. Available at: Astrophysics Data System See also: Clairaut, Théorie du mouvement des comètes, … [Theory of the movement of comets, … ] (Paris, France: Michel Lambert, 1760); see especially the preface. ^ Sagan & Druyan 1997, p. 93 ^ Wong, Yau-Chuen (2008). The Greatest Comets in History: Broom Stars and Celestial Scimitars. p. 35. ISBN 978-0-387-09513-4. ^ McKillop, Alan Dugald (1942). The Background of Thomson's Seasons. p. 67. ISBN 978-0-8166-5950-0. ^ Sagan & Druyan 1997, pp. 306–307 ^ Sagan & Druyan 1997, p. 85 ^ Sagan & Druyan 1997, p. 126 ^ Whipple, F. L. (1950). "A comet model. I. The acceleration of Comet Encke". The Astrophysical Journal. 111: 375. Bibcode:1950ApJ...111..375W. doi:10.1086/145272. ^ Calder, Nigel (13 October 2005). Magic Universe:A Grand Tour of Modern Science. p. 156. ISBN 978-0-19-162235-9. ^ Küppers, Michael; O'Rourke, Laurence; Bockelée-Morvan, Dominique; Zakharov, Vladimir; Lee, Seungwon; von Allmen, Paul; Carry, Benoît; Teyssier, David; Marston, Anthony; Müller, Thomas; Crovisier, Jacques; Barucci, M. Antonietta; Moreno, Raphael (2014). "Localized sources of water vapour on the dwarf planet (1) Ceres". Nature. 505 (7484): 525–527. Bibcode:2014Natur.505..525K. doi:10.1038/nature12918. ISSN 0028-0836. PMID 24451541. ^ a b Harrington, J.D. (22 January 2014). "Herschel Telescope Detects Water on Dwarf Planet - Release 14-021". NASA. Retrieved 22 January 2014. ^ Zubritsky, Elizabeth; Neal-Jones, Nancy (11 August 2014). "RELEASE 14-038 - NASA's 3-D Study of Comets Reveals Chemical Factory at Work". NASA. Retrieved 12 August 2014. ^ Cordiner, M.A.; et al. (11 August 2014). "Mapping the Release of Volatiles in the Inner Comae of Comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) Using the Atacama Large Millimeter/Submillimeter Array". 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The Catalogue of Comet Discoveries. Retrieved 18 July 2015. ^ a b c d Bowdoin Van Riper, A (2002). Science in Popular Culture: A Reference Guide. pp. 27–29. ISBN 978-0-313-31822-1. ^ Ridpath, Ian (3 July 2008). "Awaiting the Comet". A brief history of Halley's Comet. Retrieved 15 August 2013. ^ Ayres Jr, B. Drummond (29 March 1997). "Families Learning of 39 Cultists Who Died Willingly". New York Times. Retrieved 20 August 2013. According to material the group posted on its Internet site, the timing of the suicides were probably related to the arrival of the Hale–Bopp comet, which members seemed to regard as a cosmic emissary beckoning them to another world ^ Brin, David (6 December 1987). "The View From Halley's Comet : 2061: ODYSSEY THREE by Arthur C. Clarke". Los Angeles Times. ^ Active Asteroid P/2013 P5 Bibliography[edit] Sagan, Carl; Druyan, Ann (1997). Comet. London: Headline. ISBN 978-0-7472-7664-7.Further reading[edit] Schechner, Sara J. (1997). Comets, Popular Culture, and the Birth of Modern Cosmology. Princeton University Press. ISBN 978-0-691-01150-9. Brandt, John C.; Chapman, Robert D. (2004). Introduction to Comets (2nd ed.). Cambridge University Press. ISBN 978-0-521-80863-7.External links[edit] Cometat Wikipedia's sister projects Definitions from Wiktionary Media from Wikimedia Commons Quotations from Wikiquote Texts from Wikisource Textbooks from Wikibooks Resources from Wikiversity Comets at Curlie Comets at NASA's Solar System Exploration International Comet Quarterly by Harvard University Catalogue of the Solar System Small Bodies Orbital Evolution Science Demos: Make a Comet by the National High Magnetic Field LaboratoryvteCometsFeatures Nucleus Coma Tails Antitail Comet dust Meteor showerTypes Periodic Numbered Lost Long period Halley-type Jupiter-family Encke-type Main-belt Non-periodic Near-parabolic Hyperbolic Unknown-orbit Great Comet Sungrazing (Kreutz) Extinct Rock Exocomet InterstellarRelated Naming of comets Centaur Comet discoverers LINEAR Extraterrestrial atmosphere Oort cloud Small Solar System body AsteroidExploration List of missions to comets List of comets visited by spacecraftLatest C/2018 C2 (Lemmon) C/2017 U7 1I/2017 U1 ʻOumuamua C/2016 U1 (NEOWISE) C/2015 G2 (MASTER) C/2015 F5 (SWAN-XingMing) C/2015 F3 C/2015 ER61 (PANSTARRS) C/2014 Q2 (Lovejoy) C/2014 E2 (Jacques) C/2013 US10 (Catalina) C/2013 A1 (Siding Spring) C/2012 S4 (PANSTARRS) C/2012 K1 (PANSTARRS)Culture andspeculation Antimatter comet Comets in fiction list Comet vintagesLists of comets (more)PeriodiccometsUntil 1985(all) 1P/Halley 2P/Encke 3D/Biela 4P/Faye 5D/Brorsen 6P/d'Arrest 7P/Pons–Winnecke 8P/Tuttle 9P/Tempel 10P/Tempel 11P/Tempel–Swift–LINEAR 12P/Pons–Brooks 13P/Olbers 14P/Wolf 15P/Finlay 16P/Brooks 17P/Holmes 18D/Perrine–Mrkos 19P/Borrelly 20D/Westphal 21P/Giacobini–Zinner 22P/Kopff 23P/Brorsen–Metcalf 24P/Schaumasse 25D/Neujmin 26P/Grigg–Skjellerup 27P/Crommelin 28P/Neujmin 29P/Schwassmann–Wachmann 30P/Reinmuth 31P/Schwassmann–Wachmann 32P/Comas Solà 33P/Daniel 34D/Gale 35P/Herschel–Rigollet 36P/Whipple 37P/Forbes 38P/Stephan–Oterma 39P/Oterma 40P/Väisälä 41P/Tuttle–Giacobini–Kresák 42P/Neujmin 43P/Wolf–Harrington 44P/Reinmuth 45P/Honda–Mrkos–Pajdušáková 46P/Wirtanen 47P/Ashbrook–Jackson 48P/Johnson 49P/Arend–Rigaux 50P/Arend 51P/Harrington 52P/Harrington–Abell 53P/Van Biesbroeck 54P/de Vico–Swift–NEAT 55P/Tempel–Tuttle 56P/Slaughter–Burnham 57P/du Toit–Neujmin–Delporte 58P/Jackson–Neujmin 59P/Kearns–Kwee 60P/Tsuchinshan 61P/Shajn–Schaldach 62P/Tsuchinshan 63P/Wild 64P/Swift–Gehrels 65P/Gunn 66P/du Toit 67P/Churyumov–Gerasimenko 68P/Klemola 69P/Taylor 70P/Kojima 71P/Clark 72P/Denning–Fujikawa 73P/Schwassmann–Wachmann 74P/Smirnova–Chernykh 75D/Kohoutek 76P/West–Kohoutek–Ikemura 77P/Longmore 78P/Gehrels 79P/du Toit–Hartley 80P/Peters–Hartley 81P/Wild 82P/Gehrels 83D/Russell 84P/Giclas 85D/Boethin 86P/Wild 87P/Bus 88P/Howell 89P/Russell 90P/Gehrels 91P/Russell 92P/Sanguin 93P/Lovas 94P/Russell 95P/Chiron 96P/Machholz 97P/Metcalf–Brewington 98P/Takamizawa 99P/Kowal 100P/Hartley 101P/Chernykh 102P/ShoemakerAfter 1985(notable) 103P/Hartley 105P/Singer Brewster 107P/Wilson–Harrington 109P/Swift–Tuttle 111P/Helin–Roman–Crockett 114P/Wiseman–Skiff 128P/Shoemaker–Holt 139P/Väisälä–Oterma 144P/Kushida 147P/Kushida–Muramatsu 153P/Ikeya–Zhang 163P/NEAT 168P/Hergenrother 169P/NEAT 177P/Barnard 178P/Hug–Bell 205P/Giacobini 209P/LINEAR 238P/Read 246P/NEAT 252P/LINEAR 255P/Levy 273P/Pons–Gambart 276P/Vorobjov 289P/Blanpain 311P/PANSTARRS 322P/SOHO 332P/Ikeya-Murakami 354P/LINEAR 362PP/1997 B1 (Kobayashi) P/2010 B2 (WISE) P/2011 NO1 (Elenin)Comet-likeasteroids 596 Scheila 2060 Chiron (95P) 4015 Wilson–Harrington (107P) 7968 Elst–Pizarro (133P) 165P/LINEAR 166P/NEAT 167P/CINEOS 60558 Echeclus (174P) 118401 LINEAR (176P) 238P/Read 259P/Garradd 311P/PANSTARRS 324P/La Sagra P/2010 A2 (LINEAR) P/2012 F5 (Gibbs) P/2012 T1 (PANSTARRS) P/2013 R3 (Catalina-PANSTARRS) (300163) 2006 VW139LostRecovered 11P/Tempel–Swift–LINEAR 15P/Finlay 17P/Holmes 27P/Crommelin 54P/de Vico–Swift–NEAT 55P/Tempel–Tuttle 57P/du Toit–Neujmin–Delporte 69P/Taylor 72P/Denning–Fujikawa 80P/Peters–Hartley 97P/Metcalf–Brewington 107P/Wilson–Harrington 109P/Swift–Tuttle 113P/Spitaler 122P/de Vico 157P/Tritton 177P/Barnard 205P/Giacobini 206P/Barnard–Boattini 271P/van Houten–Lemmon 273P/Pons–Gambart 289P/BlanpainDestroyed 3D/Biela 73P/Schwassmann–Wachmann D/1993 F2 (Shoemaker–Levy 9)Not found D/1770 L1 (Lexell) 5D/Brorsen 18D/Perrine–Mrkos 20D/Westphal 25D/Neujmin 34D/Gale 75D/Kohoutek 83D/Russell 85D/BoethinVisited byspacecraft 21P/Giacobini–Zinner (1985) 1P/Halley (1986) 26P/Grigg–Skjellerup (1992) 19P/Borrelly (2001) 81P/Wild (2004) 9P/Tempel (2005, 2011) C/2006 P1 (2007) 103P/Hartley (2010) 67P/Churyumov–Gerasimenko (2014)Non-Periodiccomets(notable)Until 1910 C/-43 K1 (Caesar's Comet) X/1106 C1 (Great Comet of 1106) C/1577 V1 (Great Comet of 1577) C/1652 Y1 C/1680 V1 (Great Comet of 1680, Kirsch's Comet, Newton's Comet)) C/1702 H1 (Comet of 1702) C/1729 P1 (Comet of 1729, Comet Sarabat) C/1743 X1 (Great Comet of 1744, Comet Klinkenberg-Chéseaux) C/1760 A1 (Great Comet of 1760) C/1769 P1 (Great Comet of 1769) C/1807 R1 (Great Comet of 1807) C/1811 F1 (Great Comet of 1811) C/1819 N1 (Great Comet of 1819) C/1823 Y1 (Great Comet of 1823) C/1843 D1 (Great March Comet of 1843) C/1847 T1 (Miss Mitchell's Comet) C/1858 L1 (Comet Donati) C/1861 G1 (Comet Thatcher) C/1861 J1 (Great Comet of 1861) C/1865 B1 (Great Southern Comet of 1865) X/1872 X1 (Pogson's Comet) C/1874 H1 (Comet Coggia) C/1881 K1 (Comet Tebbutt) C/1882 R1 (Great Comet of 1882) C/1887 B1 (Great Southern Comet of 1887) C/1890 V1 (Comet Zona) C/1901 G1 (Great Comet of 1901) C/1910 A1 (Great January Comet of 1910)After 1910 C/1911 O1 (Brooks) C/1911 S3 (Beljawsky) C/1927 X1 (Skjellerup–Maristany) C/1931 P1 (Ryves) C/1941 B2 (de Kock-Paraskevopoulos) [de] C/1947 X1 (Southern Comet) [de] C/1948 V1 (Eclipse) C/1956 R1 (Arend–Roland) C/1957 P1 (Mrkos) [de] C/1961 O1 (Wilson-Hubbard) [de] C/1961 R1 (Humason) C/1962 C1 (Seki-Lines) [de] C/1963 R1 (Pereyra) C/1965 S1 (Ikeya-Seki) C/1969 Y1 (Bennett) C/1970 K1 (White–Ortiz–Bolelli) C/1973 E1 (Kohoutek) C/1975 V1 (West) C/1980 E1 (Bowell) C/1983 H1 (IRAS–Araki–Alcock) C/1989 X1 (Austin) C/1989 Y1 (Skorichenko–George) C/1992 J1 (Spacewatch–Rabinowitz) C/1993 Y1 (McNaught–Russell) C/1995 O1 (Hale–Bopp) C/1996 B2 (Hyakutake) C/1997 L1 (Zhu–Balam) C/1998 H1 (Stonehouse) C/1998 J1 (SOHO) C/1999 F1 (Catalina) C/1999 S4 (LINEAR) C/2000 U5 (LINEAR) C/2000 W1 (Utsunomiya-Jones) C/2001 OG108 (LONEOS) C/2001 Q4 (NEAT) C/2002 T7 (LINEAR) C/2004 F4 (Bradfield) [de] C/2004 Q2 (Machholz) C/2006 A1 (Pojmański) C/2006 M4 (SWAN) C/2006 P1 (McNaught) C/2007 E2 (Lovejoy) C/2007 F1 (LONEOS) C/2007 K5 (Lovejoy) C/2007 N3 (Lulin) C/2007 Q3 (Siding Spring) C/2007 W1 (Boattini) C/2008 Q1 (Matičič) C/2009 F6 (Yi–SWAN) C/2009 R1 (McNaught) C/2010 X1 (Elenin) C/2011 L4 (PANSTARRS) C/2011 W3 (Lovejoy) C/2012 E2 (SWAN) C/2012 F6 (Lemmon) C/2012 K1 (PANSTARRS) C/2012 S1 (ISON) C/2012 S4 (PANSTARRS) C/2013 A1 (Siding Spring) C/2013 R1 (Lovejoy) C/2013 US10 (Catalina) C/2013 V5 (Oukaimeden) C/2014 E2 (Jacques) C/2014 Q2 (Lovejoy) C/2015 ER61 (PANSTARRS) C/2015 V2 (Johnson) 1I/2017 U1 ʻOumuamua C/2017 U7 C/2018 C2 (Lemmon)After 1910(by name) Arend–Roland Austin Beljawsky Bennett Boattini Bowell Bradfield [de] Brooks Catalina C/1999 F1 C/2013 US10 de Kock–Paraskevopoulos [de] Eclipse Elenin Hale-Bopp Humason Hyakutake Ikeya-Seki IRAS–Araki–Alcock ISON Jacques Johnson Kohoutek Lemmon C/2012 F6 C/2018 C2 LINEAR C/1999 S4 C/2000 U5 C/2002 T7 LONEOS C/2001 OG108 C/2007 F1 Lovejoy C/2007 E2 C/2007 K5 C/2011 W3 C/2013 R1 C/2014 Q2 Lulin Machholz Matičič McNaught C/2006 P1 C/2009 R1 McNaught–Russell Mrkos [de] NEAT Oukaimeden ʻOumuamua Pan-STARRS C/2011 L4 C/2012 K1 C/2012 S4 311P C/2015 ER61 Pereyra Pojmański Ryves Seki–Lines [de] Siding Spring C/2007 Q3 C/2013 A1 Skjellerup–Maristany Skorichenko–George SOHO Southern [de] Spacewatch–Rabinowitz Stonehouse SWAN C/2006 M4 C/2012 E2 Utsunomiya–Jones West White–Ortiz–Bolelli Wilson–Hubbard [de] Yi–SWAN Zhu–Balam Category Commons Wikinews vteThe 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For more information about comet check the Wikipedia article here

ZME Science posts about comet

Gosse Bluff – the resting place of a comet

Tue, Sep 15, 2009

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