# Comet <!-- SOLSIM:BEGIN g31 — Solar System explorer state (hand-built on wt-core, specs/solar/); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Comets in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=comets&embed=1" data-title="Comets in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=comets`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.* <!-- SOLSIM:END --> *Try: set the speed to 1 year/s and watch Encke lap the Sun every 3.3 seconds while Halley crawls round its long ellipse in the opposite direction to the planets; drag the year slider to 1997 to find Hale–Bopp near perihelion; then drag it to 2017 and 2019 and follow ʻOumuamua and Borisov through the inner system on open paths that never close.* A **comet** is a small icy body that, when it comes close enough to the [[Sun]], warms and releases gas and dust. The escaping material forms a coma, a vast, thin atmosphere around the solid nucleus, and often tails that stream away from the Sun under sunlight and the [[Solar_wind|solar wind]]. Nuclei, loose mixtures of ice, dust and rock, range from a few hundred metres to tens of kilometres across.[^greenberg1998][^fernandez2000] Most comets travel on long, eccentric orbits. Short-period comets come mainly from the [[Kuiper_belt|Kuiper belt]] and [[Scattered_disc|scattered disc]] beyond [[Neptune]]; long-period comets come from the [[Oort_cloud|Oort cloud]], whose members, perhaps a trillion of them, are nudged inward by passing stars and the tide of the galaxy.[^duncan2008][^erickson2003] Unlike most [[Asteroid|asteroids]], comets contain volatile ices and so develop comae and tails; they are thought to have formed farther from the Sun, beyond [[Jupiter]].[^esa-faq][^ishii2008] Some 4,584 comets were known by November 2021, and roughly one a year becomes visible to the unaided eye.[^mpc][^licht1999] The explorer at the top of this page shows five of them together: the short-period comets Encke and [[Halley's_Comet|Halley]], the long-period Hale–Bopp, and the interstellar visitors [[1I/ʻOumuamua|ʻOumuamua]] and 2I/Borisov on open, hyperbolic paths. ## Etymology The word comes through Old English and Latin *cometa* from the Greek *komētēs*, "wearing long hair", from *komē*, the hair of the head. Greek writers already used *astēr komētēs*, the long-haired star, for a comet, the hair being its tail.[^etymonline] The old astronomical symbol for a comet, ☄, shows a small disc with three hair-like strands streaming from it.[^americana1920] ## Physical characteristics ### Nucleus The nucleus is the solid body of the comet: rock and dust bound with frozen [[Water|water]], carbon dioxide, carbon monoxide, methane and ammonia.[^greenberg1998] Fred Whipple's 1950 model called it a "dirty snowball"; observations of the Deep Impact collision with comet 9P/Tempel 1 in 2005, including those made by ESA's Rosetta spacecraft, suggested that "icy dirtball", with more dust than ice, may fit better.[^whipple1950][^the2005] The surface is usually dry and dusty, and the ices lie beneath a crust. Nuclei contain organic compounds, and the amino acid glycine was confirmed in comet dust returned by the Stardust mission in 2009.[^meech1997][^elsila2009] Nuclei are among the darkest objects in the [[PORTAL_Solar_System|Solar System]]. Halley's reflects about 4% of the light falling on it, and comet Borrelly less; the dark crust is thought to be tar-like organic residue left after the lighter ices have escaped, and by absorbing sunlight it drives the heating that powers activity.[^asp1986][^jpl-borrelly] Known nuclei have mean densities around 0.6 g/cm³, less than ice, which implies a porous, loosely bound structure.[^britt2006] | Comet | Size (km) | Density (g/cm³) | Mass (kg) | |---|---|---|---| | 1P/Halley | 15 × 8 × 8 | 0.6 | 3 × 10¹⁴[^asp1986][^sagdeev1988] | | 9P/Tempel 1 | 7.6 × 4.9 | 0.62 | 7.9 × 10¹³[^britt2006] | | 67P/Churyumov–Gerasimenko | 4.1 × 3.3 × 1.8 | 0.47 | 1.0 × 10¹³[^esa-67p][^esa-67pmass] | The masses follow from the sizes. An ellipsoid 15 × 8 × 8 km has a volume of about 500 km³, which at 0.6 g/cm³ gives 3 × 10¹⁴ kg (derived). Such small bodies have very weak [[Gravity|gravity]]: the escape speed from the surface of 67P, about 2 km from its centre, is under 1 m/s (derived), and for that reason nuclei keep irregular shapes. Rosetta and its lander Philae found that 67P has no magnetic field, and Philae identified sixteen organic compounds at the surface, four of them new to comets.[^esa-magnet][^bibring2015] ### Coma Gas and dust leaving the nucleus form the coma. Within about 3–4 AU of the Sun, water makes up as much as 90% of the escaping volatiles; sunlight breaks the water molecules apart, mainly by photodissociation.[^combi2004] The nucleus is seldom more than a few tens of kilometres across, but the coma can grow far larger: a month after its outburst of October 2007, comet 17P/Holmes had a thin dust cloud larger than the Sun.[^jewitt-holmes] In 1996 comet Hyakutake was found to emit X-rays, unexpected from so cold a body. Thomas Cravens explained them in 1997: highly charged ions in the solar wind capture electrons from the coma's gas and then emit X-rays as they settle.[^lisse1996][^cravens1997][^lisse2001] ### Bow shock Ultraviolet sunlight ionises the coma's gas, and the solar wind, meeting these ions, is slowed over a large region upstream of the comet, forming a bow shock. Comets have no magnetic field of their own; like [[Venus]] and [[Mars]], they have an induced magnetosphere, built from the solar wind's field as it drapes around the ionised gas.[^tsurutani2023] ### Tails A comet can show a dust tail, an ion tail, both or neither. Radiation pressure pushes dust grains about the width of a human hair away from the Sun, and because each grain continues on its own orbit the dust tail curves gently. Gas ionised by sunlight is caught by the magnetic field carried in the solar wind, and the ion tail, a stream of [[Plasma_(physics)|plasma]], points straight away from the Sun.[^lang2011] Larger, pebble-sized particles stay close to the comet's orbit, and when Earth lies near the plane of that orbit they can appear as an antitail pointing toward the Sun. ### Jets Uneven heating can make gas burst from weak spots in the surface like geysers; such jets can change a nucleus's spin and even split it.[^hubble-jets] Images of comet Hartley 2 in 2010 showed jets driven by sublimating carbon dioxide ice carrying dust and chunks of water ice into the coma.[^baldwin2010][^chang2010] ## Orbital characteristics Most comets follow elongated ellipses that bring them close to the Sun briefly and carry them far out for the rest of each [[Orbit|orbit]].[^st-andrews] By [[Kepler's_laws_of_planetary_motion|Kepler's laws]], a comet spends most of its time near aphelion, moving slowly. ### Encke-type comet Comet Encke's orbit stays inside Jupiter's: its perihelion is 0.34 AU and its aphelion 4.1 AU, and it returns every 3.3 years.[^jpl-sbdb] Comets of this kind, with aphelia below 4 AU, are called Encke-type.[^horner2003] Jupiter-family comets (JFCs) have periods under 20 years and inclinations below about 30°; Halley-type comets (HTCs) have periods of 20–200 years and inclinations of any value. As of July 2025 there were 74 known Encke-type comets, 109 HTCs and 815 JFCs.[^sheppard-jfc][^duncan2008][^jpl-sbdbq] Main-belt comets form a separate group on nearly circular orbits within the [[Asteroid_belt|asteroid belt]].[^andrews2022] ### Short period Short-period comets have periods under 200 years, and most orbit in the same direction as the planets, close to the [[Ecliptic|ecliptic]].[^duncan1988][^delsemme2001] Many have aphelia near the orbit of a giant planet and are said to belong to its family, Jupiter's being the largest; they are thought to have been captured from longer orbits by that planet.[^wilson1909][^horner2003] Their orbits point to a source in the Kuiper belt and scattered disc.[^duncan1988] ### Intermediate period Comets with periods between about 30 and 200 years have been called intermediate-period comets, although definitions vary; in one scheme they are those with aphelia beyond about 35 AU but not far beyond.[^horner2003] ### Long period Long-period comets have periods from 200 years to millions of years, highly eccentric orbits and inclinations spread in all directions, as Jan Oort found in 1950.[^oort1950] Hale–Bopp, with an aphelion of about 354 AU and an inclination of 89°, is an example.[^jpl-sbdb] Galactic tides and passing stars suffice to send such comets inward from the Oort cloud, and about half are ejected from the Solar System by the planets on their first pass.[^vokrouhlicky2019][^rickman2014] Three objects have been found on orbits with eccentricities well above 1, showing they came from outside the Solar System: [[1I/ʻOumuamua|ʻOumuamua]] (e ≈ 1.20), 2I/Borisov (3.36) and 3I/ATLAS (6.14).[^jpl-sbdb] ʻOumuamua showed no coma, though its non-gravitational acceleration suggests outgassing; Borisov and ATLAS both have comae.[^gohd2018][^grossman2019] ### Exocomets Comets orbiting other stars were first found around the young star Beta Pictoris in 1987, through absorption by gas released as they fell toward it.[^beust1990] Transits of comet tails were identified in data from the Kepler space telescope in 2018 and from TESS at Beta Pictoris in 2019.[^rappaport2018][^zieba2019] Exocomets now appear to be common around other stars.[^iglesias2025] ## Effects of comets ### Connection to meteor showers Dust grains too large to be blown away spread along a comet's orbit, and when [[Earth]] crosses such a trail a [[Meteor_shower|meteor shower]] results; recent, dense trails give brief, intense showers, and older ones longer, weaker displays.[^lyzenga1999] The Perseids come from Comet Swift–Tuttle each August, and Halley's Comet feeds the Orionids in October.[^meteorshowersonline] ### Comets and impact on life Many comets struck the young Earth. Some scientists think they brought much of the water in Earth's oceans; others doubt that they supplied more than a small share.[^muir2007] Comets contain organic molecules, which has led to proposals that they carried ingredients for life to Earth, and laboratory impacts of icy targets produce amino acids by shock synthesis.[^fernandez2006][^martins2013] Comet impacts may also have delivered some of the water found in lunar samples.[^nasa-lunarwater] ### Fear of comets In Europe, fear of comets as divine warnings peaked between about 1200 and 1650. After the Great Comet of 1618, Gotthard Arthusius published a list of disasters that comets supposedly foretold.[^arthusius1619] Using Edmond Halley's orbits, William Whiston argued in 1711 that the comet of 1680 had a 574-year period and had caused the biblical flood, which revived fear of comets as physical threats.[^ley1967] In 1910 cyanogen was found in the spectrum of Halley's Comet, and with Earth due to pass through its tail, some people bought "anti-comet pills".[^nyt1910][^coffey2009] ## Formation Comets are thought to be leftover building blocks of the outer planetary system, condensed from the gas and dust of the [[Protoplanetary_disk|protoplanetary disc]]. How microscopic grains grew into kilometre-sized nuclei is debated. In one model small particles stick together in successive collisions, but growth stalls near a metre. In another, centimetre-sized pebbles are concentrated by streaming in the gas until the cloud collapses under its own gravity, though keeping such a pebble pile cold and fragile against radioactive heating is a problem.[^weissman2020] As the giant planets' orbits shifted, the planetesimals were scattered into the Kuiper belt, the scattered disc and the Oort cloud, and some were trapped as trojans of Jupiter and Neptune. These regions act as cold stores, at about 40 K in the Kuiper belt and scattered disc and about 10 K in the Oort cloud.[^weissman2020] ## Reservoirs Active comets are on unstable orbits and last only a few hundred thousand years, so they must be continually replaced from distant reservoirs.[^levison2007] ### Oort cloud The Oort cloud is a roughly spherical swarm beginning somewhere between 2,000 and 5,000 AU and extending to about 50,000 AU, with some estimates of the outer edge at 100,000–200,000 AU.[^levison2007][^duncan2008] Its outer part is only weakly bound to the Sun and supplies long-period and possibly Halley-type comets. The inner part, the [[Hills_cloud|Hills cloud]] proposed by Jack Hills in 1981, may hold tens or hundreds of times more nuclei and could restock the outer cloud.[^hills1981][^levison2001] ### Kuiper Belt Nearer the Sun, the Kuiper belt and the scattered disc hold the reservoir of inactive nuclei from which [[Neptune]]'s gravity gradually releases the short-period comets, by way of the centaurs.[^levison2007] ## Fate The most common end for a comet is ejection from the Solar System, followed by disintegration, tidal break-up, loss of its volatiles, and collision with a larger body.[^weissman2020] ### Departure (ejection) from Solar System A comet travelling faster than the local escape speed leaves on a hyperbola. Comets native to the Solar System are ejected only by encounters, mostly with Jupiter: C/1980 E1 (Bowell), once on an orbit of about 7 million years, reached an eccentricity of 1.057 after passing Jupiter in 1980.[^hughes1991][^horizons-bowell] ### Extinction A comet that has lost its surface volatiles becomes dormant or extinct: a dark, inert body that can look like an asteroid.[^jewitt2004] Jupiter-family comets stay active for about 10,000 years, or roughly 1,000 orbits, while long-period comets fade much faster: only 10% survive more than 50 close passages.[^whitman2006] About 6% of near-Earth asteroids are thought to be extinct comet nuclei.[^whitman2006] ### Breakup and collisions Nuclei can be fragile. Comet Shoemaker–Levy 9 was torn apart by Jupiter in July 1992, and in July 1994 its fragments struck the planet over six days, the first collision between two Solar System bodies to be observed.[^kronk-sl9][^jpl-sl9] Biela's Comet split in 1846 and was never seen after 1852, though meteor showers appeared in 1872 and 1885 at its expected returns.[^andromedids] 73P/Schwassmann–Wachmann broke into many pieces from 1995 to 2006.[^spitzer2006] Thermal stress, gas pressure and impacts are all suspected causes.[^boehnhardt2004] ## Nomenclature Halley's Comet was the first named after an astronomer, because Edmond Halley showed that the comets of 1531, 1607 and 1682 were one body and predicted its return.[^ridpath-halley] Encke's and Biela's comets were likewise named for those who computed their orbits; later, periodic comets usually took their discoverers' names.[^icq-names] Since 1995 the IAU has used designations modelled on those of minor planets: a prefix, such as P/ for periodic or C/ for non-periodic comets, then the year and a code for the half-month of discovery.[^iau-naming] In 2019 the second interstellar object was named 2I/Borisov after its discoverer, Gennadiy Borisov.[^iau2019] ## History of study ### Early observations and thought Comets appear in records as old as Chinese oracle bones.[^cam-oracle] Aristotle placed them in the upper atmosphere, below the Moon, and this view dominated European thought for nearly two thousand years.[^heidarzadeh2008][^barker1988] Seneca the Younger objected in the 1st century CE that comets move too regularly to be atmospheric.[^sagan1997] In India, the 6th-century astronomers Varāhamihira and Bhadrabahu regarded comets as periodic.[^kelley2011][^sharma1987] In 1301 Giotto painted Halley's Comet, with unusual realism, as the Star of Bethlehem.[^olson1984] ### Modern astronomy Tycho Brahe and Michael Maestlin measured the parallax of the Great Comet of 1577 and showed it to be at least four times as distant as the [[Moon]], well beyond the atmosphere.[^barker2002][^eso-history] [[Isaac_Newton|Isaac Newton]] showed in the *Principia* in 1687 that a body moving under inverse-square gravity follows a conic section, and fitted a parabola to the comet of 1680.[^newton1687] Halley applied the method to the comets recorded between 1337 and 1698 and predicted the return of the one now named for him; Alexis Clairaut, Jérôme Lalande and Nicole-Reine Lepaute refined the date of its 1759 perihelion to within a month.[^halley1705][^broughton1985] Friedrich Bessel proposed in 1836 that jets of evaporating gas could alter a comet's orbit, and in 1950 Whipple's icy-nucleus model explained both activity and such non-gravitational forces.[^sagan1997][^whipple1950] ### Spacecraft missions A fleet of spacecraft, including ESA's Giotto and the Soviet Vega 1 and 2, met Halley's Comet in 1986 and photographed its nucleus.[^kerr1986] Deep Space 1 found the surface of Borrelly hot, dry and very dark in 2001.[^jpl-borrelly] Deep Impact struck Tempel 1 in July 2005 and found that most water ice lies below the surface.[^brown2006] Stardust returned dust from comet Wild 2 that included minerals formed at high temperature, evidence that material from the hot inner disc was mixed outward.[^rincon2006][^llnl2008] Rosetta orbited 67P from 2014, and on 12 November 2014 its lander Philae made the first landing on a comet.[^esa-philae] ## Classification Astronomers classify comets by orbit, using the Tisserand parameter with respect to Jupiter and the planets that control their perihelia and aphelia, and more informally by appearance.[^horner2003] ### Great comets About once a decade a comet becomes bright enough for casual observers to notice, and is called a great comet.[^yeomans2007] Brightness is hard to predict: Kohoutek in 1973 was expected to be spectacular and disappointed, while West in 1976 exceeded expectations.[^atkinson2012][^kronk-west] Hyakutake in 1996 and Hale–Bopp in 1997 ended a long gap, and C/2006 P1 (McNaught) in January 2007 was the brightest in over 40 years.[^hubble-mcnaught] ### Sungrazing comets Sungrazers pass within a few million kilometres of the Sun. Small ones evaporate, and tidal forces often fragment larger ones.[^mobberley2010][^opik1966] About 90% of the sungrazers seen by the SOHO spacecraft belong to the Kreutz group, the fragments of one giant comet.[^bailey1992] The Marsden and Kracht groups appear related to comet 96P/Machholz.[^sekanina2005] ### Unusual comets Comet 29P/Schwassmann–Wachmann travels on a nearly circular orbit between Jupiter and [[Saturn]].[^kronk-29p] 2060 Chiron, between Saturn and [[Uranus]], was classed as an asteroid until a faint coma was found.[^kronk-chiron] ### Centaurs Centaurs share traits of asteroids and comets. Some are classed as both: 60558 Echeclus was found inactive and later developed a coma, earning the comet designation 174P.[^horner2004][^choi2006] ## Observation In the outer Solar System comets are frozen, inactive and too small to detect directly; reported statistical detections of comet-sized objects in the Kuiper belt with the Hubble Space Telescope have been questioned.[^cochran1995][^brown1997] Most comets are telescopic, but a few each decade become visible to the unaided eye.[^pasachoff2000] Amateurs still find them, including online: SOHO's 2,000th comet was found by Michał Kusiak in images downloaded on 26 December 2010.[^soho2010] ### Naming convention The Minor Planet Center assigns designations. P/ marks a period under 200 years and C/ a longer or open orbit; X/ is used when no reliable orbit exists and D/ for a periodic comet that has disappeared. The year and a letter for the half-month of discovery follow.[^mpc-designation] ## In popular culture Popular images of comets draw on the old tradition of comets as omens. Mark Twain, born in a year when Halley's Comet appeared, predicted that he would "go out with it", and died in 1910 at its next return.[^vanriper2002] In 1997 the appearance of Hale–Bopp was linked to the mass suicide of the Heaven's Gate group.[^ayres1997] Fiction has used comet impacts as disasters averted by heroism, as in the 1998 films *Deep Impact* and *Armageddon*, and as apocalypse, as in *Lucifer's Hammer*; Arthur C. Clarke's *2061: Odyssey Three* sends a crewed expedition to Halley's Comet.[^vanriper2002][^brin1987] ## Gallery Comets look very different from one another. Close-up images from spacecraft show dark, irregular nuclei, from the elongated body of Halley to the two-lobed shape of 67P, while ground-based images show everything from faint fuzzy spots to great comets whose tails stretch across the sky.[^kerr1986][^esa-67p] ## See also - [[Halley's_Comet]] · [[Interstellar_object]] · [[1I/ʻOumuamua]] - [[Oort_cloud]] · [[Kuiper_belt]] · [[Scattered_disc]] · [[Centaur_(small_Solar_System_body)]] - [[Meteor_shower]] · [[Meteoroid]] · [[Near-Earth_object]] ## References ### Footnotes Derived values: the ellipsoid volume is (4/3)π × 7.5 × 4 × 4 km³ ≈ 503 km³; at 600 kg/m³ this gives 3.0 × 10¹⁴ kg. The escape speed from 67P uses v = √(2GM/r) with M = 1.0 × 10¹³ kg and r ≈ 2 km, giving about 0.8 m/s. ### Citations [^greenberg1998]: Greenberg, J. M. (1998). "Making a comet nucleus". *Astronomy & Astrophysics* 330: 375. Bibcode 1998A&A...330..375G. [^fernandez2000]: Fernández, Y. R. (2000). "The nucleus of comet Hale–Bopp (C/1995 O1): size and activity". *Earth, Moon, and Planets* 89: 3–25. https://doi.org/10.1023/A:1021545031431 [^duncan2008]: Duncan, M. J. (2008). "Dynamical origin of comets and their reservoirs". *Space Science Reviews* 138: 109–126. https://doi.org/10.1007/s11214-008-9405-5 [^erickson2003]: Erickson, J. (2003). *Asteroids, Comets, and Meteorites: Cosmic Invaders of the Earth*. Infobase, p. 123. ISBN 978-0-8160-4873-1. [^esa-faq]: European Space Agency. "What is the difference between asteroids and comets?". Rosetta frequently asked questions. https://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions [^ishii2008]: Ishii, H. A.; Bradley, J. P.; Dai, Z. R.; Chi, M.; Kearsley, A. T.; Burchell, M. J.; et al. (2008). "Comparison of comet 81P/Wild 2 dust with interplanetary dust from comets". *Science* 319: 447–450. https://doi.org/10.1126/science.1150683 [^mpc]: Minor Planet Center. 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"NASA spacecraft finds comet has hot, dry surface". http://www.jpl.nasa.gov/releases/2002/release_2002_80.html [^britt2006]: Britt, D. T.; Consolmagno, G. J.; Merline, W. J. (2006). "Small body density and porosity: new data, new insights". *37th Lunar and Planetary Science Conference*, abstract 2214. https://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf [^sagdeev1988]: Sagdeev, R. Z.; Elyasberg, P. E.; Moroz, V. I. (1988). "Is the nucleus of Comet Halley a low density body?". *Nature* 331: 240. https://doi.org/10.1038/331240a0 [^esa-67p]: European Space Agency (22 January 2015). "Comet vital statistics". https://www.esa.int/spaceinimages/Images/2015/01/Comet_vital_statistics [^esa-67pmass]: Baldwin, E. (21 August 2014). "Determining the mass of comet 67P/C-G". ESA Rosetta blog. http://blogs.esa.int/rosetta/2014/08/21/determining-the-mass-of-comet-67pc-g/ [^esa-magnet]: Bauer, M. (14 April 2015). "Rosetta and Philae find comet not magnetised". 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The bulk statistics". *Monthly Notices of the Royal Astronomical Society* 354: 798–810. https://doi.org/10.1111/j.1365-2966.2004.08240.x [^choi2006]: Choi, Y.-J.; Weissman, P. R.; Polishook, D. (2006). "(60558) 2000 EC98". *IAU Circular* 8656: 2. [^cochran1995]: Cochran, A. L.; Levison, H. F.; Stern, S. A.; Duncan, M. J. (1995). "The discovery of Halley-sized Kuiper belt objects using the Hubble Space Telescope". *The Astrophysical Journal* 455: 342. https://doi.org/10.1086/176581 [^brown1997]: Brown, M. E.; Kulkarni, S. R.; Liggett, T. J. (1997). "An analysis of the statistics of the Hubble Space Telescope Kuiper belt object search". *The Astrophysical Journal* 490: L119–L122. https://doi.org/10.1086/311009 [^pasachoff2000]: Pasachoff, J. M. (2000). *A Field Guide to the Stars and Planets*. Houghton Mifflin, p. 75. ISBN 978-0-395-93432-6. [^soho2010]: NASA SOHO (28 December 2010). 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University of Arizona Press. - Sagan, C.; Druyan, A. (1997). *Comet*. Random House. ## External links - NASA Science: Comets. https://science.nasa.gov/solar-system/comets/ - *International Comet Quarterly* (Harvard). http://www.icq.eps.harvard.edu/ - Minor Planet Center: cometary designation system. https://www.minorplanetcenter.net/iau/lists/CometResolution.html - ESA Rosetta mission. https://www.esa.int/Science_Exploration/Space_Science/Rosetta - JPL Small-Body Database. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Comet) : [Wikitube](https://en.wikitube.io/wiki/Comet) · pinned revision [1374859653](https://en.wikipedia.org/w/index.php?oldid=1374859653) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-026 · explorer state `?obj=comets`.* <!-- hub_tags: Life_Physics · PORTAL_Solar_System -->