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An interstellar object is an astronomical object (such as an asteroid, a comet, or a rogue planet, but not a star or stellar remnant) in interstellar space that is not gravitationally bound to a star. This term can also be applied to an object that is on an interstellar trajectory but is temporarily passing close to a star, such as certain asteroids and comets (including exoasteroids exocomets). In the latter case, the object may be called an interstellar interloper.

The first interstellar objects discovered were rogue planets, planets ejected from their original stellar system (e.g., OTS 44 or Cha 110913−773444), though they are difficult to distinguish from sub-brown dwarfs, planet-mass objects that formed in interstellar space as stars do.

The first interstellar object which was discovered traveling through the Solar System was 1I/ʻOumuamua in 2017. The second was 2I/Borisov in 2019. They both possess significant hyperbolic excess velocity, indicating they did not originate in the Solar System. The discovery of ʻOumuamua inspired the tentative identification of CNEOS 2014-01-08, also known as the Manus Island fireball, as an interstellar object that impacted the Earth by astronomers Amir Siraj and Avi Loeb in 2019. This was supported by the U.S. Space Command in 2022 based on the object's velocity relative to the Sun, In May 2023, astronomers reported the possible capture of other interstellar objects in Near Earth Orbit (NEO) over the years. however, NASA and Other astronomers doubt this, and still other experts found Earth-related explanations for the purported meteorite impact instead.

The interstellar objects were once bound to a host star and have become unbound since. Different processes can cause planets and smaller objects (planetesimals) to become unbound from their host star.

Nomenclature

With the first discovery of an interstellar object in the Solar System, the IAU has proposed a new series of small-body designations for interstellar objects, the I numbers, similar to the comet numbering system. The Minor Planet Center will assign the numbers. Provisional designations for interstellar objects will be handled using the C/ or A/ prefix (comet or asteroid), as appropriate.

Overview

Interstellar velocity inbound (${\displaystyle v_{\infty }}$)

Object	Velocity
C/2012 S1 (ISON) (weakly hyperbolic Oort Cloud comet)	0.2 km/s 0.04 au/yr
Voyager 1 (For comparison)	16.9 km/s 3.57 au/yr
1I/2017 U1 (ʻOumuamua)	26.33 km/s 5.55 au/yr
2I/Borisov	32.1 km/s 6.77 au/yr
2014Jan08 bolide (in peer review, no widespread consensus)	43.8 km/s 9.24 au/yr

Astronomers estimate that several interstellar objects of extrasolar origin (like ʻOumuamua) pass inside the orbit of Earth each year, and that 10,000 are passing inside the orbit of Neptune on any given day.

Interstellar comets occasionally pass through the inner Solar System and approach with random velocities, mostly from the direction of the constellation Hercules because the Solar System is moving in that direction, called the solar apex. Until the discovery of 'Oumuamua, the fact that no comet with a speed greater than the Sun's escape velocity had been observed was used to place upper limits to their density in interstellar space. A paper by Torbett indicated that the density was no more than 10 (10 trillion) comets per cubic parsec. Other analyses, of data from LINEAR, set the upper limit at 4.5×10/AU, or 10 (1 trillion) comets per cubic parsec. A more recent estimate by David C. Jewitt and colleagues, following the detection of 'Oumuamua, predicts that "The steady-state population of similar, ~100 m scale interstellar objects inside the orbit of Neptune is ~1×10, each with a residence time of ~10 years."

Current models of Oort cloud formation predict that more comets are ejected into interstellar space than are retained in the Oort cloud, with estimates varying from 3 to 100 times as many. Other simulations suggest that 90–99% of comets are ejected. There is no reason to believe comets formed in other star systems would not be similarly scattered. Amir Siraj and Avi Loeb demonstrated that the Oort Cloud could have been formed from ejected planetesimals from other stars in the Sun's birth cluster. Both researchers proposed a search for ʻOumuamua-like objects which are trapped in the Solar System as a result of losing orbital energy through a close encounter with Jupiter.

It is possible for objects orbiting a star to be ejected due to interaction with a third massive body, thereby becoming interstellar objects. Such a process was initiated in the early 1980s when C/1980 E1, initially gravitationally bound to the Sun, passed near Jupiter and was accelerated sufficiently to reach escape velocity from the Solar System. This changed its orbit from elliptical to hyperbolic and made it the most eccentric known object at the time, with an eccentricity of 1.057. It is heading for interstellar space.

Due to present observational difficulties, an interstellar object can usually only be detected if it passes through the Solar System, where it can be distinguished by its strongly hyperbolic trajectory and hyperbolic excess velocity of more than a few km/s, proving that it is not gravitationally bound to the Sun. In contrast, gravitationally bound objects follow elliptic orbits around the Sun. (There are a few objects whose orbits are so close to parabolic that their gravitationally bound status is unclear.)

An interstellar comet can probably, on rare occasions, be captured into a heliocentric orbit while passing through the Solar System. Computer simulations show that Jupiter is the only planet massive enough to capture one, and that this can be expected to occur once every sixty million years. Comets Machholz 1 and Hyakutake C/1996 B2 are possible examples of such comets. They have atypical chemical makeups for comets in the Solar System.

Recent research suggests that asteroid 514107 Kaʻepaokaʻawela may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun. In addition, comet C/2018 V1 (Machholz-Fujikawa-Iwamoto) has a significant probability (72.6%) of having an extrasolar provenance although an origin in the Oort cloud cannot be excluded. Harvard astronomers suggest that matter—and potentially dormant spores—can be exchanged across vast distances. The detection of ʻOumuamua crossing the inner Solar System confirms the possibility of a material link with exoplanetary systems.

Interstellar visitors in the Solar System cover the whole range of sizes – from kilometer large objects down to submicron particles. Also, interstellar dust and meteoroids carry with them valuable information from their parent systems. Detection of these objects along the continuum of sizes is, however, not evident (see Figure). The smallest interstellar dust particles are filtered out of the solar system by electromagnetic forces, while the largest ones are too sparse to obtain good statistics from in situ spacecraft detectors. Discrimination between interstellar and interplanetary populations can be a challenge for intermediate (0.1–1 micrometer) sizes. These can vary widely in velocity and directionality. The identification of interstellar meteoroids, observed in the Earth's atmosphere as meteors, is highly challenging and requires high accuracy measurements and appropriate error examinations. Otherwise, measurement errors can transfer near-parabolic orbits over the parabolic limit and create an artificial population of hyperbolic particles, often interpreted as of interstellar origin. Large interstellar visitors like asteroids and comets were detected the first time in the solar system in 2017 (1I/'Oumuamua) and 2019 (2I/Borisov) and are expected to be detected more frequently with new telescopes, e.g. the Vera Rubin Observatory. Amir Siraj and Avi Loeb have predicted that the Vera C. Rubin Observatory will be capable of detecting an anisotropy in the distribution of interstellar objects due to the Sun's motion relative to the Local Standard of Rest and identify the characteristic ejection speed of interstellar objects from their parent stars.

In May 2023, astronomers reported the possible capture of other interstellar objects in Near Earth Orbit (NEO) over the years.

Confirmed objects

1I/2017 U1 (ʻOumuamua)

A dim object was discovered on October 19, 2017, by the Pan-STARRS telescope, at an apparent magnitude of 20. The observations showed that it follows a strongly hyperbolic trajectory around the Sun at a speed greater than the solar escape velocity, in turn meaning that it is not gravitationally bound to the Solar System and likely to be an interstellar object. It was initially named C/2017 U1 because it was assumed to be a comet, and was renamed to A/2017 U1 after no cometary activity was found on October 25. After its interstellar nature was confirmed, it was renamed to 1I/ʻOumuamua – "1" because it is the first such object to be discovered, "I" for interstellar, and "'Oumuamua" is a Hawaiian word meaning "a messenger from afar arriving first".

The lack of cometary activity from ʻOumuamua suggests an origin from the inner regions of whatever stellar system it came from, losing all surface volatiles within the frost line, much like the rocky asteroids, extinct comets and damocloids we know from the Solar System. This is only a suggestion, as ʻOumuamua might very well have lost all surface volatiles to eons of cosmic radiation exposure in interstellar space, developing a thick crust layer after it was expelled from its parent system.

ʻOumuamua has an eccentricity of 1.199, which was the highest eccentricity ever observed for any non-artificial object in the Solar System by a wide margin prior to the discovery of comet 2I/Borisov in August 2019.

In September 2018, astronomers described several possible home star systems from which ʻOumuamua may have begun its interstellar journey.

2I/Borisov

The object was discovered on 30 August 2019 at MARGO, Nauchnyy, Crimea by Gennadiy Borisov using his custom-built 0.65-meter telescope. On 13 September 2019, the Gran Telescopio Canarias obtained a low-resolution visible spectrum of 2I/Borisov that revealed that this object has a surface composition not too different from that found in typical Oort Cloud comets. The IAU Working Group for Small Body Nomenclature kept the name Borisov, giving the comet the interstellar designation of 2I/Borisov. On 12 March 2020, astronomers reported observational evidence of "ongoing nucleus fragmentation" from Borisov.

Candidates

In 2007, Afanasiev et al. reported the likely detection of a multi-centimeter intergalactic meteor hitting the atmosphere above the Special Astrophysical Observatory of the Russian Academy of Sciences on July 28, 2006.

In November 2018, Harvard astronomers Amir Siraj and Avi Loeb reported that there should be hundreds of 'Oumuamua-size interstellar objects in the Solar System, based on calculated orbital characteristics, and presented several centaur candidates such as 2017 SV₁₃ and 2018 TL₆. These are all orbiting the Sun, but may have been captured in the distant past. Both researchers have proposed methods for increasing the discovery rate of interstellar objects that include stellar occultations, optical signatures from impacts with the moon or the Earth's atmosphere, and radio flares from collisions with neutron stars.

2014 interstellar meteor

CNEOS 2014-01-08 (also known as Interstellar meteor 1; IM1), a meteor with a mass of 0.46 tons and width of 0.45 m (1.5 ft), burned up in the Earth's atmosphere on January 8, 2014. A 2019 preprint suggested this meteor had been of interstellar origin. It had a heliocentric speed of 60 km/s (37 mi/s) and an asymptotic speed of 42.1 ± 5.5 km/s (26.2 ± 3.4 mi/s), and it exploded at 17:05:34 UTC near Papua New Guinea at an altitude of 18.7 km (61,000 ft). After declassifying the data in April 2022, the U.S. Space Command, based on information collected from its planetary defense sensors, confirmed the velocity of the potential interstellar meteor. In 2023, The Galileo Project completed an expedition to retrieve small fragments of the apparently peculiar meteor. Claims about their findings have been doubted by their peers according to a report in The New York Times. Further related studies were reported on 1 September 2023.

Other astronomers doubt the interstellar origin because the meteoroid catalog used does not report uncertainties on the incoming velocity. The validity of any single data point (especially for smaller meteoroids) remains questionable. In November 2022, a paper was published, claiming the anomalous properties (including its high strength and strongly hyperbolic trajectory) of CNEOS 2014-01-08 are better described as measurement error rather than genuine parameters. Successful retrieval of any meteoroid fragments is highly unlikely. Common micrometeorites would be indistinguishable from one another.

2017 interstellar meteor

CNEOS 2017-03-09 (aka Interstellar meteor 2; IM2), a meteor with a mass of roughly 6.3 tons, burned up in the Earth's atmosphere on March 9, 2017. Similar to IM1, it has a high mechanical strength. In September 2022, astronomers Amir Siraj and Avi Loeb reported the discovery of a candidate interstellar meteor, CNEOS 2017-03-09, that impacted Earth in 2017 and is considered, based in part on the high material strength of the meteor, to be a possible interstellar object.

Hypothetical missions

With current space technology, close visits and orbital missions are challenging due to their high speeds, though not impossible.

The Initiative for Interstellar Studies (i4is) launched in 2017 Project Lyra to assess the feasibility of a mission to ʻOumuamua. Several options for sending a spacecraft to ʻOumuamua within a time-frame of 5 to 25 years were suggested. One option is using first a Jupiter flyby followed by a close solar flyby at 3 solar radii (2.1×10^ km; 1.3×10^ mi) in order to take advantage of the Oberth effect. Different mission durations and their velocity requirements were explored with respect to the launch date, assuming direct impulsive transfer to the intercept trajectory.

The Comet Interceptor spacecraft by ESA and JAXA, planned to launch in 2029, will be positioned at the Sun-Earth L₂ point to wait for a suitable long-period comet to intercept and flyby for study. In case that no suitable comet is identified during its 3-year wait, the spacecraft could be tasked to intercept an interstellar object in short notice, if reachable.

See also

• Global catastrophic risk – Hypothetical global-scale disaster risk
• Hyperbolic asteroid – Astronomical object not orbiting the Sun
• List of artificial objects leaving the Solar System
• List of hyperbolic comets – Comets that may not be orbiting the Sun
• List of Solar System objects by greatest aphelion
• Rogue black hole

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66. Siraj, Amir; Loeb, Abraham (2020-02-26). "Detecting Interstellar Objects through Stellar Occultations". The Astrophysical Journal. 891 (1): L3. arXiv:2001.02681. Bibcode:2020ApJ...891L...3S. doi:10.3847/2041-8213/ab74d9. ISSN 2041-8213. S2CID 210116475.
67. Siraj, Amir; Loeb, Abraham (2020-08-01). "A real-time search for interstellar impacts on the moon". Acta Astronautica. 173: 53–55. arXiv:1908.08543. Bibcode:2020AcAau.173...53S. doi:10.1016/j.actaastro.2020.04.006. ISSN 0094-5765. S2CID 201645069.
68. Siraj, Amir; Loeb, Abraham (2019-09-19). "Radio Flares from Collisions of Neutron Stars with Interstellar Asteroids". Research Notes of the AAS. 3 (9): 130. arXiv:1908.11440. Bibcode:2019RNAAS...3..130S. doi:10.3847/2515-5172/ab43de. ISSN 2515-5172. S2CID 201698501.
69. August 2019, Mike Wall 30 (30 August 2019). "A Telescope Orbiting the Moon Could Spy 1 Interstellar Visitor Per Year". Space.com. Retrieved 2020-11-14.{{cite web}}: CS1 maint: numeric names: authors list (link)
70. Pultarova, Tereza (3 November 2022). "Confirmed! A 2014 meteor is Earth's 1st known interstellar visitor - Interstellar space rocks might be falling to Earth every 10 years". Space.com. Retrieved 4 November 2022.
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72. ^ Loeb, Avi (23 September 2022). "The discovery of a second interstellar meteor". TheDebrief.org. Retrieved 24 September 2022.
73. Billings, Lee (23 April 2019). "Did a Meteor from Another Star Strike Earth in 2014? – Questionable data cloud the potential discovery of the first known interstellar fireball". Scientific American. Retrieved 12 April 2022.
74. Choi, Charles Q. (16 April 2019). "The First Known Interstellar Meteor May Have Hit Earth in 2014 – The 3-foot-wide rock rock visited us three years before 'Oumuamua". Space.com. Retrieved 12 April 2022.
75. Specktor, Brandon (11 April 2022). "An interstellar object exploded over Earth in 2014, declassified government data reveal – Classified data prevented scientists from verifying their discovery for 3 years". Live Science. Retrieved 12 April 2022.
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External links

• Engelhardt, Toni; Jedicke, Robert; Vereš, Peter; Fitzsimmons, Alan; Denneau, Larry; Beshore, Ed; Meinke, Bonnie (2017). "An Observational Upper Limit on the Interstellar Number Density of Asteroids and Comets". The Astronomical Journal. 153 (3): 133. arXiv:1702.02237. Bibcode:2017AJ....153..133E. doi:10.3847/1538-3881/aa5c8a. S2CID 54893830.

v t e Comets
Features Nucleus Coma Tails Antitail Comet dust Meteor shower Types 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 Exocomet Interstellar Related Naming of comets Observational history of comets Centaur Comet discoverers LINEAR Extraterrestrial atmosphere Oort cloud Small Solar System body Asteroid Exploration List of missions to comets List of comets visited by spacecraft Latest C/2024 S1 (ATLAS) C/2024 G3 (ATLAS) C/2023 P1 (Nishimura) C/2023 H2 (Lemmon) C/2023 E1 (ATLAS) C/2023 A3 (Tsuchinshan–ATLAS) C/2022 E3 (ZTF) C/2021 O3 (PanSTARRS) C/2021 J1 (Maury-Attard) C/2021 A1 (Leonard) C/2020 F8 (SWAN) C/2020 F5 (MASTER) C/2020 F3 (NEOWISE) C/2019 Y4 (ATLAS) C/2019 Y1 (ATLAS) C/2019 U6 (Lemmon) 2I/Borisov P/2019 LD2 (ATLAS) C/2018 Y1 (Iwamoto) C/2018 C2 (Lemmon) C/2017 U7 C/2017 K2 (PanSTARRS) C/2016 U1 (NEOWISE) C/2015 V2 (Johnson) C/2015 G2 (MASTER) C/2015 ER61 (PanSTARRS) C/2014 UN271 (Bernardinelli–Bernstein) C/2014 Q2 (Lovejoy) C/2014 Q1 (PanSTARRS) Culture and speculation Antimatter comet Comets in fiction Comet vintages
Lists of comets (more) Periodic comets Until 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 After 1985 (notable) 88P/Howell 92P/Sanguin 96P/Machholz 97P/Metcalf–Brewington 103P/Hartley 107P/Wilson–Harrington 108P/Ciffréo 109P/Swift–Tuttle 122P/de Vico 126P/IRAS 141P/Machholz 144P/Kushida 147P/Kushida–Muramatsu 153P/Ikeya–Zhang 156P/Russell–LINEAR 161P/Hartley–IRAS 162P/Siding Spring 168P/Hergenrother 169P/NEAT 177P/Barnard 178P/Hug–Bell 205P/Giacobini 209P/LINEAR 238P/Read 246P/NEAT 249P/LINEAR 252P/LINEAR 255P/Levy 273P/Pons–Gambart 289P/Blanpain 311P/PanSTARRS 322P/SOHO 323P/SOHO 332P/Ikeya–Murakami 333P/LINEAR 354P/LINEAR 362P 460P/PanSTARRS Comet-like asteroids 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 331P/Gibbs 354P/LINEAR 358P/PANSTARRS P/2013 R3 (Catalina-PANSTARRS) (300163) 2006 VW139 Lost Recovered 9P/Tempel 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 113P/Spitaler 122P/de Vico 157P/Tritton 205P/Giacobini 206P/Barnard–Boattini 226P/Pigott–LINEAR–Kowalski 271P/van Houten–Lemmon 289P/Blanpain Destroyed 3D/Biela 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/Boethin Visited by spacecraft 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) Near-Parabolic comets (notable) Until 1990 C/-43 K1 (Caesar's Comet) X/1106 C1 (Great Comet of 1106) C/1264 N1 (Great Comet of 1264) C/1402 D1 (Great Comet of 1402) C/1471 Y1 (Great Comet of 1472) 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/1901 G1 (Great Comet of 1901) C/1910 A1 (Great January Comet of 1910) C/1911 O1 (Brooks) C/1911 S3 (Beljawsky) C/1927 X1 (Skjellerup–Maristany) C/1931 P1 (Ryves) C/1941 B2 (de Kock-Paraskevopoulos) C/1947 X1 (Southern Comet) C/1948 V1 (Eclipse) C/1956 R1 (Arend–Roland) C/1957 P1 (Mrkos) C/1961 O1 (Wilson-Hubbard) [de] C/1961 R1 (Humason) C/1962 C1 (Seki-Lines) C/1963 A1 (Ikeya) C/1963 R1 (Pereyra) C/1964 N1 (Ikeya) C/1965 S1 (Ikeya-Seki) C/1969 T1 (Tago-Sato-Kosaka) [de] 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 W1 (Aarseth-Brewington) C/1989 X1 (Austin) C/1989 Y1 (Skorichenko–George) After 1990 C/1990 K1 (Levy) 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 WM1 (LINEAR) C/2001 A2 (LINEAR) C/2001 OG108 (LONEOS) C/2001 Q4 (NEAT) C/2002 T7 (LINEAR) C/2002 V1 (NEAT) C/2004 F4 (Bradfield) 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 N3 (Lulin) C/2007 Q3 (Siding Spring) C/2007 W1 (Boattini) 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/2013 A1 (Siding Spring) C/2013 R1 (Lovejoy) C/2013 US10 (Catalina) C/2013 V5 (Oukaimeden) C/2014 E2 (Jacques) C/2014 Q1 (PanSTARRS) C/2014 Q2 (Lovejoy) C/2015 ER61 (PanSTARRS) C/2015 V2 (Johnson) C/2017 K2 (PanSTARRS) 1I/2017 U1 ʻOumuamua C/2018 Y1 (Iwamoto) 2I/Borisov C/2019 U6 (Lemmon) C/2019 Y4 (ATLAS) C/2020 F3 (NEOWISE) C/2020 F8 (SWAN) C/2021 A1 (Leonard) C/2022 E3 (ZTF) C/2023 A3 (Tsuchinshan–ATLAS) C/2023 P1 (Nishimura) After 1910 (by name) Aarseth-Brewington Arend–Roland Austin Beljawsky Bennett Boattini Borisov Bowell Bradfield Brooks Catalina C/1999 F1 C/2013 US10 de Kock–Paraskevopoulos Eclipse Elenin Hale-Bopp Humason Hyakutake Ikeya C/1963 A1 C/1964 N1 Ikeya-Seki IRAS–Araki–Alcock ISON Iwamoto Jacques Johnson Kohoutek Lemmon C/2012 F6 C/2018 C2 C/2019 U6 Leonard Levy LINEAR C/1999 S4 C/2000 WM1 C/2001 A2 C/2002 T7 LONEOS C/2001 OG108 C/2007 F1 Lovejoy C/2007 E2 C/2011 W3 C/2013 R1 C/2014 Q2 Lulin Machholz McNaught C/2006 P1 C/2009 R1 McNaught–Russell Mrkos NEAT C/2001 Q4 C/2002 V1 NEOWISE Nishimura Oukaimeden ʻOumuamua Pan-STARRS C/2011 L4 C/2012 K1 311P/PanSTARRS C/2014 Q1 C/2015 ER61 C/2017 K2 Pereyra Pojmański Ryves Seki–Lines Siding Spring C/2007 Q3 C/2013 A1 Skjellerup–Maristany Skorichenko–George SOHO Southern Spacewatch–Rabinowitz Stonehouse SWAN C/2006 M4 C/2012 E2 C/2020 F8 Tago-Sato-Kosaka [de] Tsuchinshan–ATLAS West White–Ortiz–Bolelli Wilson–Hubbard [de] Yi–SWAN Zhu–Balam ZTF
Category

v t e Exoplanets
Planet Definition IAU Planetary science
Main topics	Exoplanet Exoplanet orbital and physical parameters Methods of detecting exoplanets Planetary system Planet-hosting stars
Sizes and types	Terrestrial Carbon planet Coreless planet Desert planet Dwarf planet Hycean planet Ice planet Iron planet (Super-Mercury) Lava planet Ocean world Mega-Earth Sub-Earth Super-Earth Gaseous Eccentric Jupiter Mini-Neptune (Gas dwarf) Helium planet Hot Jupiter Hot Neptune Gas giant Ice giant Super-Jupiter Super-Neptune Super-puff Ultra-hot Jupiter Ultra-hot Neptune Other types Blanet Brown dwarf Chthonian planet Circumbinary planet Circumtriple planet Disrupted planet Double planet Ecumenopolis Eyeball planet Giant planet Mesoplanet Planemo Planet/Brown dwarf boundary Planetesimal Protoplanet Pulsar planet Sub-brown dwarf Sub-Neptune Toroidal planet Ultra-cool dwarf Ultra-short period planet (USP)
Formation and evolution	Accretion Accretion disk Asteroid belt Circumplanetary disk Circumstellar disc Circumstellar envelope Cosmic dust Debris disk Detached object Disrupted planet Excretion disk Exozodiacal dust Extraterrestrial materials Extraterrestrial sample curation Giant-impact hypothesis Gravitational collapse Hills cloud Internal structure Interplanetary dust cloud Interplanetary medium Interplanetary space Interstellar cloud Interstellar dust Interstellar medium Interstellar space Kuiper belt List of interstellar and circumstellar molecules Merging stars Molecular cloud Nebular hypothesis Oort cloud Outer space Planetary migration Planetary system Planetesimal Planet formation Protoplanetary disk Ring system Rubble pile Sample-return mission Scattered disc Star formation
Systems	Exocomet Interstellar Exomoon Tidally detached Rogue planet Orbits Retrograde Trojan Mean-motion resonances Titius–Bode law
Host stars	A B Binary star Brown dwarfs F/Yellow-white dwarfs G/Yellow dwarfs Herbig Ae/Be K/Orange dwarfs M/Red dwarfs Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giants
Detection	Astrometry Direct imaging list Microlensing list Polarimetry Timing list Radial velocity list Transit method list Transit-timing variation
Habitability	Astrobiology Astrooceanography Circumstellar habitable zone Earth analog Extraterrestrial liquid water Galactic habitable zone Habitability of binary star systems Habitability of F-type main-sequence star systems Habitability of K-type main-sequence star systems Habitability of natural satellites Habitability of neutron star systems Habitability of red dwarf systems Habitability of yellow dwarf systems Habitable zone for complex life List of potentially habitable exoplanets Tholin Superhabitable planet
Catalogues	Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database Open Exoplanet Catalogue
Lists	Exoplanetary systems Host stars Multiplanetary systems Stars with proto-planetary discs Exoplanets Discoveries Extremes Firsts Nearest Largest Heaviest Terrestrial candidates Kepler 1–500 501–1000 1001–1500 1501–2000 K2 Potentially habitable Proper names Discovered exoplanets by year before 2000 2000–2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Other	Carl Sagan Institute Exoplanet naming convention Exoplanet phase curves Exoplanetary Circumstellar Environments and Disk Explorer Extragalactic planet Extrasolar planets in fiction Geodynamics of terrestrial exoplanets Neptunian desert Nexus for Exoplanet System Science Planets in globular clusters Small planet radius gap Sudarsky's gas giant classification
Discoveries of exoplanets Search projects

• Astronomy
• Stars
• Spaceflight
• Outer space
• Solar System

• Interstellar objects
• Exoplanetology
• Stellar astronomy