Editing Comet (section)

== Orbital characteristics ==

Most comets are [[small Solar System bodies]] with elongated [[elliptical orbit]]s 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.<ref>{{cite web |url=http://www.st-andrews.ac.uk/~bds2/ltsn/ljm/JAVA/COMETORB/COMET.HTM |title=The Orbit of a Comet |publisher=University of St Andrews |access-date=1 September 2013}}</ref> Comets are often classified according to the length of their [[orbital period]]s: The longer the period the more elongated the ellipse.

=== {{anchor|Short-period comet}} Short period ===
{{Main|List of numbered comets|List of Halley-type comets}}

[[List of periodic comets|Periodic comets]] or short-period comets are generally defined as those having orbital periods of less than 200 years.<ref>{{cite journal |title=The origin of short-period comets |journal=The Astrophysical Journal Letters |first1=Martin |last1=Duncan |first2=Thomas |last2=Quinn |first3=Scott |last3=Tremaine |display-authors=1 |volume=328 |pages=L69–L73 |date=May 1988 |doi=10.1086/185162 |bibcode=1988ApJ...328L..69D|doi-access=free }}</ref> They usually orbit more-or-less in the [[ecliptic]] plane in the same direction as the planets.<ref>{{cite book |url=https://books.google.com/books?id=Ox5hCOc9A2AC&pg=PA117 |page=117 |title=Our Cosmic Origins: From the Big Bang to the Emergence of Life and Intelligence |isbn=978-0-521-79480-0 |last=Delsemme |first=Armand H. |date=2001|publisher=Cambridge University Press }}</ref> 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".<ref name=Wilson1909>{{cite journal |last=Wilson |first=H. C. |title=The Comet Families of Saturn, Uranus and Neptune |journal=Popular Astronomy |volume=17 |pages=629–633 |date=1909 |bibcode=1909PA.....17..629W}}</ref> Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits.<ref>{{cite web |url=http://www.uwgb.edu/dutchs/PLANETS/Comets.HTM |title=Comets |first=Steven |last=Dutch |publisher=Natural and Applied Sciences, University of Wisconsin |access-date=31 July 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130729122906/http://www.uwgb.edu/dutchs/PLANETS/Comets.HTM |archive-date=29 July 2013}}</ref>

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).<ref>{{cite web |url=http://www.dtm.ciw.edu/users/sheppard/satellites/jf.html |title=The Jupiter Family Comets |publisher=Department of Terrestrial Magnetism Carnegie Institution of Washington |access-date=11 August 2013}}</ref><ref name="britastro">{{cite web |url=http://www.britastro.org/projectalcock/Comets%20where%20are%20they.htm |title=Comets – where are they ? |date=6 November 2012 |publisher=British Astronomical Association |access-date=11 August 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130805211248/http://www.britastro.org/projectalcock/Comets%20where%20are%20they.htm |archive-date=5 August 2013}}</ref> 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).<ref name="Morbidelli2006">{{cite journal |doi=10.1007/s11214-008-9405-5 |title=Dynamical Origin of Comets and Their Reservoirs |date=2008 |last1=Duncan |first1=Martin J. |journal=Space Science Reviews |volume=138 |issue=1–4 |pages=109–126 |bibcode=2008SSRv..138..109D|s2cid=121848873 }}</ref><ref name=jewitt2002>{{Cite journal |doi=10.1086/338692 |title=From Kuiper Belt Object to Cometary Nucleus: The Missing Ultrared Matter |date=2002 |last1=Jewitt |first1=David C. |journal=The Astronomical Journal |volume=123 |issue=2 |pages=1039–1049 |bibcode=2002AJ....123.1039J|s2cid=122240711 |doi-access=free }}</ref> {{As of| January 2025}} there are 73 known Encke-type comets (six of which are classified as [[Near-earth objects]] (NEOs)), 106 HTCs (36 of which are NEOs), and 815 JFCs (153 of which are NEOs).<ref name="SSD-JPL">{{cite web |title=Small-Body Database Query |url=https://ssd.jpl.nasa.gov/tools/sbdb_query.html#!#results |website=Solar System Dynamics - Jet Propulsion Laboratory |publisher=NASA - California Institute of Technology |access-date=2025-01-28}}</ref>

Recently discovered [[main-belt comets]] form a distinct class, orbiting in more circular orbits within the [[asteroid belt]].<ref name="NYT-20221118">{{cite news |last=Andrews |first=Robin George |title=The Mysterious Comets That Hide in the Asteroid Belt - Comets normally fly in from the far reaches of space. Yet astronomers have found them seemingly misplaced in the asteroid belt. Why are they there? |url=https://www.nytimes.com/2022/11/18/science/comet-asteroid-belt-space.html |date=18 November 2022 |work=[[The New York Times]] |accessdate=18 November 2022 }}</ref><ref>{{cite web |last=Reddy |first=Francis |title=New comet class in Earth's backyard |url=http://www.astronomy.com/sitecore/content/Home/News-Observing/News/2006/04/New%20comet%20class%20in%20Earths%20backyard.aspx?sc_lang=en |work=Astronomy |date=3 April 2006 |access-date=31 July 2013 |archive-date=24 May 2014 |archive-url=https://web.archive.org/web/20140524023305/http://www.astronomy.com/sitecore/content/Home/News-Observing/News/2006/04/New%20comet%20class%20in%20Earths%20backyard.aspx?sc_lang=en |url-status=dead }}</ref>

Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further [[Perturbation (astronomy)|gravitational perturbations]].<ref>{{cite web |url=https://www.e-education.psu.edu/astro801/content/l11_p9.html |title=Comets |publisher=The Pennsylvania State University |access-date=8 August 2013}}</ref> 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.<ref name="britastro"/> 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.<ref>{{harvnb|Sagan|Druyan|1997|pp=102–104}}</ref><ref>{{cite book |url=https://books.google.com/books?id=w7E_uwj0Lc8C&pg=PA246 |page=246 |title=In Quest of the Solar System |isbn=978-0-7637-9477-4 |last=Koupelis |first=Theo |date=2010|publisher=Jones & Bartlett Publishers }}</ref>

Based on their orbital characteristics, short-period comets are thought to originate from the [[Centaur (minor planet)|centaurs]] and the Kuiper belt/[[scattered disc]]<ref>{{cite web |last=Davidsson |first=Björn J. R. |title=Comets – Relics from the birth of the Solar System |url=http://www.astro.uu.se/~bjorn/eng_comet.html |publisher=Uppsala University |date=2008 |access-date=30 July 2013 |archive-url=https://web.archive.org/web/20130119065421/http://www.astro.uu.se/~bjorn/eng_comet.html |archive-date=19 January 2013 |url-status=dead }}</ref> —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 hypothesized its existence).<ref>{{cite journal |bibcode=1950BAN....11...91O |title=The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin |last1=Oort |first1=J. H. |volume=11 |date=1950 |pages=91 |journal=Bulletin of the Astronomical Institutes of the Netherlands}}</ref> 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.<ref>{{cite book |url=https://books.google.com/books?id=PRqVqQKao9QC&pg=PA152 |page=152 |title=Habitability and Cosmic Catastrophes |isbn=978-3-540-76945-3 |last=Hanslmeier |first=Arnold |date=2008|publisher=Springer }}</ref> When flung into the orbit of the sun, and being continuously dragged towards it, tons of matter are stripped from the comets which greatly influence their lifetime; the more stripped, the shorter they live and vice versa.<ref>{{Cite web|url=http://planetfacts.org/short-period-comet/|title=What is A Short Period Comet – Less than 200 Year Orbital Cycle|last=Rocheleau|first=Jake|date=2011-09-12|website=Planet Facts|language=en|access-date=2019-12-01}}</ref>

=== Long period ===
{{See also|List of long-period comets|List of near-parabolic comets|List of hyperbolic comets}}
[[File:Comet Kohoutek orbit p391.svg|thumb|Orbits of [[Comet Kohoutek]] (red) and Earth (blue), illustrating the high [[Orbital eccentricity|eccentricity]] of its orbit and its rapid motion when close to the Sun.]]

Long-period comets have highly [[Orbital eccentricity|eccentric]] orbits and periods ranging from 200 years to thousands or even millions of years.<ref name="SBP"/> An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System.<ref name=Elenin2011>{{cite web |url=http://spaceobs.org/en/2011/03/07/vliyanie-planet-gigantov-na-orbitu-komety-c2010-x1-elenin/ |title=Influence of giant planets on the orbit of comet C/2010 X1 |first=Leonid |last=Elenin |date=7 March 2011 |access-date=11 August 2013 |archive-date=19 March 2012 |archive-url=https://web.archive.org/web/20120319014011/http://spaceobs.org/en/2011/03/07/vliyanie-planet-gigantov-na-orbitu-komety-c2010-x1-elenin/ |url-status=dead }}</ref> For example, [[C/2006 P1|Comet McNaught]] had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage [[Epoch (astronomy)|epoch]] in January 2007 but is bound to the Sun with roughly a 92,600-year orbit because the [[Orbital eccentricity|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 [[Barycentric coordinates (astronomy)|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 [[C/1999 F1]] and [[C/2017 T2 (PANSTARRS)]] can have aphelion distances of nearly {{convert|70000|AU|pc ly|abbr=on}} with orbital periods estimated around 6&nbsp;million years.

Single-apparition or non-periodic comets are similar to long-period comets because they have [[parabolic trajectory|parabolic]] or slightly [[hyperbolic trajectory|hyperbolic]] trajectories<ref name="SBP">{{cite web |title=Small Bodies: Profile |url=http://pds.jpl.nasa.gov/planets/special/smbod.htm |publisher=NASA/JPL |date=29 October 2008 |access-date=11 August 2013}}</ref> 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.<ref>{{cite book |url=https://books.google.com/books?id=3K9Fhu2q-8gC&pg=PA21 |title=Astronomy and Astrophysics |last1=Joardar |first1=S. |last2=Bhattacharya |first2=A. B. |last3=Bhattacharya |first3=R. |display-authors=1 |page=21 |date=2008 |publisher=Jones & Bartlett Learning |isbn=978-0-7637-7786-9}}</ref> The Sun's [[Hill sphere]] has an [[unstable]] maximum boundary of {{convert|230000|AU|pc ly|abbr=on}}.<ref name=Chebotarev1964>{{cite journal |bibcode=1964SvA.....7..618C |title=Gravitational Spheres of the Major Planets, Moon and Sun |last1=Chebotarev |first1=G. A. |volume=7 |date=1964 |pages=618 |journal=Soviet Astronomy}}</ref> Only a few hundred comets have been seen to reach a hyperbolic orbit (e > 1) when near perihelion<ref name="e1">{{cite web |title=JPL Small-Body Database Search Engine: e > 1 |publisher=JPL |url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;OBJ_field=0;ORB_field=0;c1_group=ORB;c1_item=Bg;c1_op=%3E;c1_value=1;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBgBiBjBqChCk;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=BgD |access-date=13 August 2013}}</ref> that using a heliocentric unperturbed [[Two-body problem|two-body]] [[curve fitting|best-fit]] suggests they may escape the Solar System.

{{As of|2022}}, only two objects have been discovered with an [[Eccentricity (mathematics)|eccentricity]] significantly greater than one: [[ʻOumuamua|1I/ʻOumuamua]] and [[2I/Borisov]], indicating an origin outside the Solar System. While ʻOumuamua, with an eccentricity of about 1.2, 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 probably a comet.<ref name="Oumuamua">{{cite news |url=https://www.space.com/41015-interstellar-visitor-oumuamua-comet-after-all.html |title=Interstellar Visitor 'Oumuamua Is a Comet After All |work=Space.com |first=Chelsea |last=Gohd |date=27 June 2018 |access-date=27 September 2018}}</ref> On the other hand, 2I/Borisov, with an estimated eccentricity of about 3.36, has been observed to have the coma feature of comets, and is considered the first detected [[interstellar object|interstellar comet]].<ref>{{Cite news |url=https://www.sciencenews.org/article/astronomy-interstellar-comet-space |title=Astronomers have spotted a second interstellar object |work=Science News |last=Grossman |first=Lisa |date=12 September 2019 |access-date=16 September 2019}}</ref><ref name="cnn">{{cite news |url=https://www.cnn.com/2019/09/24/world/second-interstellar-visitor-confirmed-scn-trnd/ |title=2nd interstellar visitor to our solar system confirmed and named |publisher=CNN |last1=Strickland |first1=Ashley |date=27 September 2019}}</ref> Comet [[C/1980 E1]] had an orbital period of roughly 7.1&nbsp;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 solar comet with a reasonable observation arc.<ref name="C/1980E1-jpl">{{cite web |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1980E1 |title=C/1980 E1 (Bowell) |work=[[JPL Small-Body Database]] |type=1986-12-02 last obs |access-date=13 August 2013}}</ref> 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),<ref>{{cite encyclopedia |title=Comet |url=https://www.britannica.com/eb/article-54344/comet |encyclopedia=[[Encyclopædia Britannica Online]] |access-date=13 August 2013}}</ref> whereas others use it to mean exclusively short-period comets.<ref name="SBP"/> 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 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. Comets from [[interstellar space]] are moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). When such objects enter the Solar System, they have a positive [[specific orbital energy]] resulting in a positive [[hyperbolic excess velocity|velocity at infinity]] (<math>v_{\infty}\!</math>) and have notably 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 [[Order of magnitude|magnitude]].<ref>{{cite journal |title=On the nondetection of extrasolar comets |journal=The Astrophysical Journal |last1=McGlynn |first1=Thomas A. |last2=Chapman |first2=Robert D. |name-list-style=amp |volume=346 |at=L105 |date=1989 |doi=10.1086/185590 |bibcode=1989ApJ...346L.105M|doi-access=free }}</ref>

{| class="wikitable" style="width: 600px; text-align: center; font-size: 1em; margin: 0.4em auto;"
|-
|+ [[Hyperbolic comet]] discoveries<ref name="e1-name">{{cite web |title=JPL Small-Body Database Search Engine: e > 1 (sorted by name) |publisher=JPL |url=https://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;OBJ_field=0;ORB_field=0;c1_group=ORB;c1_item=Bg;c1_op=%3E;c1_value=1;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBgBiBjBqCiCkCn;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=AcD |access-date=7 December 2020}}</ref>
|-
! Year !! 2007 !! 2008 !! 2009 !! 2010 !! 2011 !! 2012 !! 2013 !! 2014 !! 2015 !! 2016 !! 2017 !! 2018 !! 2019 !! 2020
|-
! Number
| 12 || 7 || 8 || 4 || 13 || 10 || 16 || 9 || 16 || 5 || 18 || 10 || 15 || 17
|}

=== Oort cloud and Hills cloud ===
[[File:Small objects in the Solar System ESA25188647.jpg|thumb|upright=1.5|The [[Oort cloud]] thought to surround the Solar System. Showed with Kuiper Belt and Asteroid Belt for comparison.]]
{{Main|Oort cloud|Hills cloud}}
The Oort cloud is thought to occupy a vast space starting from between {{convert|2000|and|5000|AU|ly|2|abbr=on}}<ref name=book>{{cite book |chapter=Comet Populations and Cometary Dynamics |title=Encyclopedia of the Solar System |publisher=Academic Press |first1=Harold F. |last1=Levison |first2=Luke |last2=Donnes |name-list-style=amp |editor1-first=Lucy-Ann Adams |editor1-last=McFadden |editor2-first=Torrence V. |editor2-last=Johnson |editor3-first=Paul Robert |editor3-last=Weissman |edition=2nd |pages=[https://archive.org/details/encyclopediaofso0000unse_u6d1/page/575 575–588] |date=2007 |isbn=978-0-12-088589-3 |chapter-url=https://archive.org/details/encyclopediaofso0000unse_u6d1/page/575 }}</ref> to as far as {{convert|50000|AU|ly|2|abbr=on}}<ref name=Morbidelli2006/> from the Sun. This cloud encases the celestial bodies that start at the middle of the Solar System—the Sun, all the way to outer limits of the Kuiper Belt. The Oort cloud consists of viable materials necessary for the creation of celestial bodies. The Solar System's planets exist only because of the planetesimals (chunks of leftover space that assisted in the creation of planets) that were condensed and formed by the gravity of the Sun. The eccentric made from these trapped planetesimals is why the Oort Cloud even exists.<ref>{{Cite web|url=https://solarsystem.nasa.gov/solar-system/oort-cloud/in-depth|title=In Depth {{!}} Oort Cloud|website=NASA Solar System Exploration|date=14 November 2017 |access-date=2019-12-01}}</ref> Some estimates place the outer edge at between {{convert|100000|and|200000|AU|ly|2|abbr=on}}.<ref name= book /> The region can be subdivided into a spherical outer Oort cloud of {{convert|20000|-|50000|AU|ly|2|abbr=on}}, and a doughnut-shaped inner cloud, the Hills cloud, of {{convert|2000|-|20000|AU|ly|2|abbr=on}}.<ref>{{cite book |first=Lisa |last=Randall |title=Dark matter and the dinosaurs: The astounding interconnectedness of the universe |date=2015 |publisher=Harper Collins Publishers |isbn=978-0-06-232847-2 |pages=115}}</ref> 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]].<ref name=Morbidelli2006/> The inner Oort cloud is also known as the Hills cloud, named after [[Jack G. Hills]], who proposed its existence in 1981.<ref name="hills1981" /> Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo;<ref name="hills1981">{{cite journal |first=Jack G. |last=Hills |date=1981 |title=Comet showers and the steady-state infall of comets from the Oort Cloud |journal=[[The Astronomical Journal]] |volume=86 |pages=1730–1740 |bibcode=1981AJ.....86.1730H |doi=10.1086/113058|doi-access=free }}</ref><ref name="levison2001">{{cite journal |title=The Origin of Halley-Type Comets: Probing the Inner Oort Cloud |journal=[[The Astronomical Journal]] |first1=Harold F. |last1=Levison |first2=Luke |last2=Dones |first3=Martin J. |last3=Duncan |display-authors=1 |volume=121 |issue=4 |pages=2253–2267 |date=2001 |bibcode=2001AJ....121.2253L |doi=10.1086/319943|doi-access=free }}</ref><ref name="Donahue1991">{{cite book |editor-first=Thomas M. | editor-last=Donahue |others=Trivers, Kathleen Kearney and Abramson, David M. |date=1991 |title=Planetary Sciences: American and Soviet Research, Proceedings from the U.S.–U.S.S.R. Workshop on Planetary Sciences |url=http://books.nap.edu/openbook.php?record_id=1790&page=R1 |publisher=National Academy Press |page=251 |isbn=0-309-04333-6 |access-date=18 March 2008|doi=10.17226/1790 | bibcode=1991psas.conf.....D }}</ref> 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.<ref name="Julio1997">{{cite journal |first=Julio A. |last=Fernéndez |date=1997 |title=The Formation of the Oort Cloud and the Primitive Galactic Environment |url=http://www.gps.caltech.edu/classes/ge133/reading/oort.pdf |journal=[[Icarus (journal)|Icarus]] |volume=219 |issue=1 |pages=106–119 |access-date=18 March 2008 |bibcode=1997Icar..129..106F |doi=10.1006/icar.1997.5754 |archive-date=24 July 2012 |archive-url=https://web.archive.org/web/20120724192955/http://www.gps.caltech.edu/classes/ge133/reading/oort.pdf |url-status=dead }}</ref>

=== Exocomets ===
{{Main|Exocomet}}
[[Exocomet]]s beyond the Solar System have been detected and may be common in the [[Milky Way]].<ref name="berk">{{cite web |title=Exocomets may be as common as exoplanets |url=http://newscenter.berkeley.edu/2013/01/07/exocomets-may-be-as-common-as-exoplanets/ |date=7 January 2013 |publisher=UC Berkeley |access-date=30 July 2013 |last=Sanders |first=Robert}}</ref> The first exocomet system detected was around [[Beta Pictoris]], a very young [[A-type main-sequence star]], in 1987.<ref name="Space-20130107">{{cite web |title='Exocomets' Common Across Milky Way Galaxy |url=http://www.space.com/19156-exocomets-alien-solar-systems.html |date=7 January 2013 |publisher=Space.com |access-date=8 January 2013 |url-status=dead |archive-url=https://web.archive.org/web/20140916085824/http://www.space.com/19156-exocomets-alien-solar-systems.html |archive-date=16 September 2014 }}</ref><ref name="Beust1990">{{cite journal |bibcode=1990A&A...236..202B |title=The Beta Pictoris circumstellar disk. X – Numerical simulations of infalling evaporating bodies |last1=Beust |first1=H. |last2=Lagrange-Henri |first2=A.M. |last3=Vidal-Madjar |first3=A. |last4=Ferlet |first4=R. |display-authors=1 |volume=236 |date=1990 |pages=202–216 |journal=[[Astronomy & Astrophysics]] |issn=0004-6361}}</ref> A total of 11 such exocomet systems have been identified {{as of|lc=y|2013}}, using the [[Absorption spectroscopy|absorption spectrum]] caused by the large clouds of gas emitted by comets when passing close to their star.<ref name="berk"/><ref name="Space-20130107" /> For ten years the [[Kepler space telescope]] was responsible for searching for planets and other forms outside of the solar system. The first transiting exocomets were found in February 2018 by a group consisting of professional astronomers and [[Citizen science|citizen scientists]] in light curves recorded by the Kepler Space Telescope.<ref>{{Cite web|url=https://www.newsweek.com/comets-detected-outside-our-solar-system-first-time-696446|title=Astronomers have detected comets outside our solar system for the first time ever|first=Meghan|last=Bartels|date=2017-10-30|website=Newsweek|language=en|access-date=2019-12-01}}</ref><ref>{{Cite journal|last1=Rappaport|first1=S.|last2=Vanderburg|first2=A.|last3=Jacobs|first3=T.|last4=LaCourse|first4=D.|last5=Jenkins|first5=J.|last6=Kraus|first6=A.|last7=Rizzuto|first7=A.|last8=Latham|first8=D. W.|last9=Bieryla|first9=A.|last10=Lazarevic|first10=M.|last11=Schmitt|first11=A.|date=2018-02-21|title=Likely transiting exocomets detected by Kepler|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=474|issue=2|pages=1453–1468|arxiv=1708.06069|doi=10.1093/mnras/stx2735|doi-access=free |pmid=29755143|pmc=5943639|bibcode=2018MNRAS.474.1453R|issn=0035-8711}}</ref> After Kepler Space Telescope retired in October 2018, a new telescope called TESS Telescope has taken over Kepler's mission. Since the launch of TESS, astronomers have discovered the transits of comets around the star Beta Pictoris using a light curve from TESS.<ref>{{Cite web|url=https://astronomy.com/news/2019/04/tess-spots-its-first-exocomet-around-one-of-the-skys-brightest-stars|title=TESS spots its first exocomet around one of the sky's brightest stars|first=Jake|last=Parks|date=April 3, 2019|website=Astronomy.com|access-date=2019-11-25}}</ref><ref>{{Cite journal|last1=Zieba|first1=S.|last2=Zwintz|first2=K.|last3=Kenworthy|first3=M. A.|last4=Kennedy|first4=G. M.|date=2019-05-01|title=Transiting exocomets detected in broadband light by TESS in the β Pictoris system|journal=Astronomy & Astrophysics|language=en|volume=625|pages=L13|arxiv=1903.11071|doi=10.1051/0004-6361/201935552|bibcode=2019A&A...625L..13Z|s2cid=85529617|issn=0004-6361}}</ref> Since TESS has taken over, astronomers have since been able to better distinguish exocomets with the spectroscopic method. New planets are detected by the white light curve method which is viewed as a symmetrical dip in the charts readings when a planet overshadows its parent star. However, after further evaluation of these light curves, it has been discovered that the asymmetrical patterns of the dips presented are caused by the tail of a comet or of hundreds of comets.<ref>{{Cite web|url=https://www.sciencealert.com/nasa-s-new-planet-hunter-has-detected-its-first-exocomet-orbiting-an-alien-star|title=NASA's New Planet Hunter Has Detected an 'Exocomet' Orbiting an Alien Star|last=Starr|first=Michelle|website=ScienceAlert|date=2 April 2019 |language=en-gb|access-date=2019-12-01}}</ref>