The Oort cloud (/ɔːrt, ʊərt/),[1] sometimes called the Öpik–Oort cloud,[2] first described in 1950 by Dutch astronomer Jan Oort,[3] is a theoretical cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from 2,000 to 200,000 au (0.03 to 3.2 light-years).[note 1][4] It is divided into two regions: a disc-shaped inner Oort cloud (or Hills cloud) and a spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space.[4][5] The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth as far from the Sun as the Oort cloud.
The outer limit of the Oort cloud defines the cosmographic boundary of the Solar System and the extent of the Sun's Hill sphere.[6] The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way itself. These forces occasionally dislodge comets from their orbits within the cloud and send them toward the inner Solar System.[4] Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.[4][7]
Astronomers conjecture that the matter composing the Oort cloud formed closer to the Sun and was scattered far into space by the gravitational effects of the giant planets early in the Solar System's evolution.[4] Although no confirmed direct observations of the Oort cloud have been made, it may be the source of all long-period and Halley-type comets entering the inner Solar System, and many of the centaurs and Jupiter-family comets as well.[7]
Types of distant minor planets
Cis-Neptunian objects
Centaurs
Neptune trojans
Trans-Neptunian objects (TNOs)
Kuiper belt objects (KBOs)
Classical KBOs (cubewanos)
Resonant KBOs
Plutinos (2:3 resonance)
Scattered disc objects (SDOs)
Resonant SDOs
Detached objects
Extreme trans-Neptunian object
Sednoids
Oort cloud objects (ICO/OCOs)
vte
Hypothesis
There are two main classes of comet: short-period comets (also called ecliptic comets) and long-period comets (also called nearly isotropic comets). Ecliptic comets have relatively small orbits, below 10 au, and follow the ecliptic plane, the same plane in which the planets lie. All long-period comets have very large orbits, on the order of thousands of au, and appear from every direction in the sky.[8]
A. O. Leuschner in 1907 suggested that many comets believed to have parabolic orbits, and thus making single visits to the solar system, actually had elliptical orbits and would return after very long periods.[9] In 1932 Estonian astronomer Ernst Öpik postulated that long-period comets originated in an orbiting cloud at the outermost edge of the Solar System.[10] Dutch astronomer Jan Oort independently revived the idea in 1950 as a means to resolve a paradox:[11]
Over the course of the Solar System's existence the orbits of comets are unstable, and eventually dynamics dictate that a comet must either collide with the Sun or a planet or be ejected from the Solar System by planetary perturbations.
Moreover, their volatile composition means that as they repeatedly approach the Sun, radiation gradually boils the volatiles off until the comet splits or develops an insulating crust that prevents further outgassing.
Thus, Oort reasoned, a comet could not have formed while in its current orbit and must have been held in an outer reservoir for almost all of its existence.[11][12][8] He noted that there was a peak in numbers of long-period comets with aphelia (their farthest distance from the Sun) of roughly 20,000 au, which suggested a reservoir at that distance with a spherical, isotropic distribution. Those relatively rare comets with orbits of about 10,000 au have probably gone through one or more orbits through the Solar System and have had their orbits drawn inward by the gravity of the planets.[8]
Structure and composition
The presumed distance of the Oort cloud compared to the rest of the Solar System
The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 au (0.03 and 0.08 ly)[8] to as far as 50,000 au (0.79 ly)[4] from the Sun. Some estimates place the outer boundary at between 100,000 and 200,000 au (1.58 and 3.16 ly).[8] The region can be subdivided into a spherical outer Oort cloud of 20,000–50,000 au (0.32–0.79 ly), and a torus-shaped inner Oort cloud of 2,000–20,000 au (0.0–0.3 ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune.[4] The inner Oort cloud is also known as the Hills cloud, named after Jack G. Hills, who proposed its existence in 1981.[13] Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo;[13][14][15] it is seen as a possible source of new comets to resupply the 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.[16]
The outer Oort cloud may have trillions of objects larger than 1 km (0.62 mi),[4] and billions with absolute magnitudes[17] brighter than 11 (corresponding to approximately 20-kilometre (12 mi) diameter), with neighboring objects tens of millions of kilometres apart.[7][18] Its total mass is not known, but, assuming that Halley's Comet is a suitable prototype for comets within the outer Oort cloud, roughly the combined mass is 3×1025 kilograms (6.6×1025 lb), or five times that of Earth.[4][19] Earlier it was thought to be more massive (up to 380 Earth masses),[20] but improved knowledge of the size distribution of long-period comets led to lower estimates. No known estimates of the mass of the inner Oort cloud have been published.
If analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of ices such as water, methane, ethane, carbon monoxide and hydrogen cyanide.[21] However, the discovery of the object 1996 PW, an object whose appearance was consistent with a D-type asteroid[22][23] in an orbit typical of a long-period comet, prompted theoretical research that suggests that the Oort cloud population consists of roughly one to two percent asteroids.[24] Analysis of the carbon and nitrogen isotope ratios in both the long-period and Jupiter-family comets shows little difference between the two, despite their presumably vastly separate regions of origin. This suggests that both originated from the original protosolar cloud,[25] a conclusion also supported by studies of granular size in Oort-cloud comets[26] and by the recent impact study of Jupiter-family comet Tempel 1.[27]
Origin
The Oort cloud is thought to have developed after the formation of planets from the primordial protoplanetary disc approximately 4.6 billion years ago.[4] The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to the Sun as part of the same process that formed the planets and minor planets. After formation, strong gravitational interactions with young gas giants, such as Jupiter, scattered the objects into extremely wide elliptical or parabolic orbits that were subsequently modified by perturbations from passing stars and giant molecular clouds into long-lived orbits detached from the gas giant region.[4][28]
Recent research has been cited by NASA hypothesizing that a large number of Oort cloud objects are the product of an exchange of materials between the Sun and its sibling stars as they formed and drifted apart and it is suggested that many—possibly the majority—of Oort cloud objects did not form in close proximity to the Sun.[29] Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800 million years after formation, as the pace of accretion and collision slowed and depletion began to overtake supply.[4]
Models by Julio Ángel Fernández suggest that the scattered disc, which is the main source for periodic comets in the Solar System, might also be the primary source for Oort cloud objects. According to the models, about half of the objects scattered travel outward toward the Oort cloud, whereas a quarter are shifted inward to Jupiter's orbit, and a quarter are ejected on hyperbolic orbits. The scattered disc might still be supplying the Oort cloud with material.[30] A third of the scattered disc's population is likely to end up in the Oort cloud after 2.5 billion years.[31]
Computer models suggest that collisions of cometary debris during the formation period play a far greater role than was previously thought. According to these models, the number of collisions early in the Solar System's history was so great that most comets were destroyed before they reached the Oort cloud. Therefore, the current cumulative mass of the Oort cloud is far less than was once suspected.[32] The estimated mass of the cloud is only a small part of the 50–100 Earth masses of ejected material.[4]
Gravitational interaction with nearby stars and galactic tides modified cometary orbits to make them more circular. This explains the nearly spherical shape of the outer Oort cloud.[4] On the other hand, the Hills cloud, which is bound more strongly to the Sun, has not acquired a spherical shape. Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the Solar System formed as part of an embedded cluster of 200–400 stars. These early stars likely played a role in the cloud's formation, since the number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations.[33]
In June 2010 Harold F. Levison and others suggested on the basis of enhanced computer simulations that the Sun "captured comets from other stars while it was in its birth cluster." Their results imply that "a substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from the protoplanetary discs of other stars."[34][35] In July 2020 Amir Siraj and Avi Loeb found that a captured origin for the Oort Cloud in the Sun's birth cluster could address the theoretical tension in explaining the observed ratio of outer Oort cloud to scattered disc objects, and in addition could increase the chances of a captured Planet Nine.[36][37][38]
Comets
Comet Hale–Bopp, an archetypical Oort-cloud comet
Comets are thought to have two separate points of origin in the Solar System. Short-period comets (those with orbits of up to 200 years) are generally accepted to have emerged from either the Kuiper belt or the scattered disc, which are two linked flat discs of icy debris beyond Neptune's orbit at 30 au and jointly extending out beyond 100 au from the Sun. Long-period comets, such as comet Hale–Bopp, whose orbits last for thousands of years, are thought to originate in the Oort cloud. Comets modeled to be coming directly from the Oort cloud include C/2010 X1 (Elenin), Comet ISON, C/2013 A1 (Siding Spring), and C/2017 K2. The orbits within the Kuiper belt are relatively stable, and so very few comets are thought to originate there. The scattered disc, however, is dynamically active, and is far more likely to be the place of origin for comets.[8] Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs.[39] These centaurs are then sent farther inward to become the short-period comets.[40]
There are two main varieties of short-period comet: Jupiter-family comets (those with semi-major axes of less than 5 AU) and Halley-family comets. Halley-family comets, named for their prototype, Halley's Comet, are unusual in that although they are short-period comets, it is hypothesized that their ultimate origin lies in the Oort cloud, not in the scattered disc. Based on their orbits, it is suggested they were long-period comets that were captured by the gravity of the giant planets and sent into the inner Solar System.[12] This process may have also created the present orbits of a significant fraction of the Jupiter-family comets, although the majority of such comets are thought to have originated in the scattered disc.[7]
Oort noted that the number of returning comets was far less than his model predicted, and this issue, known as "cometary fading", has yet to be resolved. No dynamical process are known to explain the smaller number of observed comets than Oort estimated. Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatiles, rendering some comets invisible, or the formation of a non-volatile crust on the surface.[41] Dynamical studies of hypothetical Oort cloud comets have estimated that their occurrence in the outer-planet region would be several times higher than in the inner-planet region. This discrepancy may be due to the gravitational attraction of Jupiter, which acts as a kind of barrier, trapping incoming comets and causing them to collide with it, just as it did with Comet Shoemaker–Levy 9 in 1994.[42] An example of typical Oort cloud comet could be C/2018 F4.[43]
Tidal effects
Main article: Galactic tide
Most of the comets seen close to the Sun seem to have reached their current positions through gravitational perturbation of the Oort cloud by the tidal force exerted by the Milky Way. Just as the Moon's tidal force deforms Earth's oceans, causing the tides to rise and fall, the galactic tide also distorts the orbits of bodies in the outer Solar System. In the charted regions of the Solar System, these effects are negligible compared to the gravity of the Sun, but in the outer reaches of the system, the Sun's gravity is weaker and the gradient of the Milky Way's gravitational field has substantial effects. Galactic tidal forces stretch the cloud along an axis directed toward the galactic centre and compress it along the other two axes; these small perturbations can shift orbits in the Oort cloud to bring objects close to the Sun.[44] The point at which the Sun's gravity concedes its influence to the galactic tide is called the tidal truncation radius. It lies at a radius of 100,000 to 200,000 au, and marks the outer boundary of the Oort cloud.[8]
Some scholars theorise that the galactic tide may have contributed to the formation of the Oort cloud by increasing the perihelia (smallest distances to the Sun) of planetesimals with large aphelia (largest distances to the Sun).[45] The effects of the galactic tide are quite complex, and depend heavily on the behaviour of individual objects within a planetary system. Cumulatively, however, the effect can be quite significant: up to 90% of all comets originating from the Oort cloud may be the result of the galactic tide.[46] Statistical models of the observed orbits of long-period comets argue that the galactic tide is the principal means by which their orbits are perturbed toward the inner Solar System.[47]
Stellar perturbations and stellar companion hypotheses
Besides the galactic tide, the main trigger for sending comets into the inner Solar System is thought to be interaction between the Sun's Oort cloud and the gravitational fields of nearby stars[4] or giant molecular clouds.[42] The orbit of the Sun through the plane of the Milky Way sometimes brings it in relatively close proximity to other stellar systems. For example, it is hypothesized that 70 thousand years ago, perhaps Scholz's Star passed through the outer Oort cloud (although its low mass and high relative velocity limited its effect).[48] During the next 10 million years the known star with the greatest possibility of perturbing the Oort cloud is Gliese 710.[49] This process could also scatter Oort cloud objects out of the ecliptic plane, potentially also explaining its spherical distribution.[49][50]
In 1984, physicist Richard A. Muller postulated that the Sun has an as-yet undetected companion, either a brown dwarf or a red dwarf, in an elliptical orbit within the Oort cloud. This object, known as Nemesis, was hypothesized to pass through a portion of the Oort cloud approximately every 26 million years, bombarding the inner Solar System with comets. However, to date no evidence of Nemesis has been found, and many lines of evidence (such as crater counts), have thrown its existence into doubt.[51][52] Recent scientific analysis no longer supports the idea that extinctions on Earth happen at regular, repeating intervals.[53] Thus, the Nemesis hypothesis is no longer needed to explain current assumptions.[53]
A somewhat similar hypothesis was advanced by astronomer John J. Matese of the University of Louisiana at Lafayette in 2002. He contends that more comets are arriving in the inner Solar System from a particular region of the postulated Oort cloud than can be explained by the galactic tide or stellar perturbations alone, and that the most likely cause would be a Jupiter-mass object in a distant orbit.[54] This hypothetical gas giant was nicknamed Tyche. The WISE mission, an all-sky survey using parallax measurements in order to clarify local star distances, was capable of proving or disproving the Tyche hypothesis.[53] In 2014, NASA announced that the WISE survey had ruled out any object as they had defined it.[55]
Future exploration
Artist's impression of the TAU spacecraft
Space probes have yet to reach the area of the Oort cloud. Voyager 1, the fastest[56] and farthest[57][58] of the interplanetary space probes currently leaving the Solar System, will reach the Oort cloud in about 300 years[5][59] and would take about 30,000 years to pass through it.[60][61] However, around 2025, the radioisotope thermoelectric generators on Voyager 1 will no longer supply enough power to operate any of its scientific instruments, preventing any further exploration by Voyager 1. The other four probes currently escaping the Solar System either are already or are predicted to be non-functional when they reach the Oort cloud; however, it may be possible to find an object from the cloud that has been knocked into the inner Solar System.
In the 1980s, there was a concept for a probe that could reach 1,000 AU in 50 years, called TAU; among its missions would be to look for the Oort cloud.[62]
In the 2014 Announcement of Opportunity for the Discovery program, an observatory to detect the objects in the Oort cloud (and Kuiper belt) called the "Whipple Mission" was proposed.[63] It would monitor distant stars with a photometer, looking for transits up to 10,000 AU away.[63] The observatory was proposed for halo orbiting around L2 with a suggested 5-year mission.[63] It was also suggested that the Kepler observatory could have been capable of detecting objects in the Oort cloud.[64]
See also
Solar System portal Astronomy portal
Heliosphere
Interstellar comet
List of possible dwarf planets
List of trans-Neptunian objects
Planets beyond Neptune
Scattered disc
Tyche (hypothetical planet)
Nemesis (hypothetical star)
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John J. Matese & Jack J. Lissauer (2002-05-06). "Continuing Evidence of an Impulsive Component of Oort Cloud Cometary Flux" (PDF). Proceedings of Asteroids, Comets, Meteors - ACM 2002. International Conference, 29 July - 2 August 2002, Berlin, Germany. Asteroids. 500. University of Louisiana at Lafayette, and NASA Ames Research Center. p. 309. Bibcode:2002ESASP.500..309M. Retrieved 2008-03-21.
K. L., Luhman (7 March 2014). "A Search For A Distant Companion To The Sun With The Wide-field Infrared Survey Explorer". The Astrophysical Journal. 781 (1): 4. Bibcode:2014ApJ...781....4L. doi:10.1088/0004-637X/781/1/4.
"New Horizons Salutes Voyager". New Horizons. August 17, 2006. Archived from the original on November 13, 2014. Retrieved November 3, 2009. "Voyager 1 is escaping the solar system at 17 kilometers per second."
Clark, Stuart (September 13, 2013). "Voyager 1 leaving solar system matches feats of great human explorers". The Guardian.
"Voyagers are leaving the Solar System". Space Today. 2011. Retrieved May 29, 2014.
"It's Official: Voyager 1 Is Now In Interstellar Space". UniverseToday. 2013-09-12. Retrieved April 27, 2014.
Ghose, Tia (September 13, 2013). "Voyager 1 Really Is In Interstellar Space: How NASA Knows". Space.com. TechMedia Network. Retrieved September 14, 2013.
Cook, J.-R (September 12, 2013). "How Do We Know When Voyager Reaches Interstellar Space?". NASA / Jet Propulsion Lab. Retrieved September 15, 2013.
TAU (Thousand Astronomical Unit) mission
Charles Alcock; et al. "The Whipple Mission: Exploring the Oort Cloud and the Kuiper Belt" (PDF). Archived from the original (PDF) on 2015-11-17. Retrieved 2015-11-12.
Scientific American – Kepler Spacecraft May Be Able to Spot Elusive Oort Cloud Objects – 2010
Notes
The Oort cloud's outer limit is difficult to define as it varies over the millennia as different stars pass the Sun and thus is subject to variation. Estimates of its distance range from 50,000 to 200,000 au.
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Oort Cloud Profile by NASA's Solar System Exploration
Arnett, Bill (March 2007). "The Kuiper Belt and The Oort Cloud". Nine Planets.
Matthews, R. A. J. (1994). "The close approach of stars in the solar neighbourhood". Quarterly Journal of the Royal Astronomical Society. 35: 1. Bibcode:1994QJRAS..35....1M.
Brasser, R.; Schwamb, M. E. (2015). "Re-assessing the formation of the inner Oort cloud in an embedded star cluster - II. Probing the inner edge". Monthly Notices of the Royal Astronomical Society. 446 (4): 3788. arXiv:1411.1844. Bibcode:2015MNRAS.446.3788B. doi:10.1093/mnras/stu2374. S2CID 17001564.
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Huya Ixion Orcus 2001 QF298 2002 VR128 2002 XV93 2003 AZ84 2003 UZ413 2003 VS2 2007 JH43
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Possible
Gǃkúnǁʼhòmdímà Dziewanna 1996 GQ21 1996 TL66 2001 UR163 2002 TC302 2004 XA192 2005 QU182 2005 RM43 2006 QH181 2008 OG19 2010 KZ39 2010 RE64 2010 RF43 2010 TJ 2010 VZ98 2013 FY27 2014 AN55 2014 WK509 2018 VG18
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Possible
2003 FY128 2003 QX113 2004 XR190 2005 TB190 2008 ST291
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Possible
FarFarOut Gonggong 1999 CD158 1999 DE9 2000 YW134 2002 XW93 2010 JO179 2010 VK201 2011 FW62 2011 GM27 2013 FZ27 2014 UM33 2015 AM281 2015 RR245
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Periodic
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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 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/Shoemaker
After 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 362P P/1997 B1 (Kobayashi) P/2010 B2 (WISE) P/2011 NO1 (Elenin)
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 P/2010 A2 (LINEAR) P/2012 F5 (Gibbs) P/2012 T1 (PANSTARRS) P/2013 R3 (Catalina-PANSTARRS) (300163) 2006 VW139
Lost
Recovered
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/Blanpain
Destroyed
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/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)
Non-Periodic
comets
(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) 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/2003 A2 (Gleason) 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) C/2019 E3 (ATLAS) 2I/Borisov
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 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
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