Oort cloud

Distant planetesimals in the Solar System

This article is about the outer Oort cloud. For the inner Oort cloud, see Hills cloud.

The distance from the Oort cloud to the interior of the Solar System, and two of the nearest stars, is measured in astronomical units. The scale is logarithmic: each indicated distance is ten times farther out than the previous distance. The red arrow indicates the projected location, in 2025–2027, of the space probe Voyager 1, which may reach the Oort cloud about 300 years later.

An artist's impression of the Oort cloud and the Kuiper belt (inset); the sizes of objects are over-scaled for visibility.

The Oort cloud (pronounced /ɔːrt/ AWT or /ʊərt/ OORT),[1] sometimes called the Öpik–Oort cloud,[2] is theorized[failed verification] to be a cloud of billions of icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years).[3][4] The cloud was proposed in 1950 by the Dutch astronomer Jan Oort, in whose honor the idea was named.[5][6] Oort proposed that the bodies in this cloud replenish and keep constant the number of long-period comets entering the inner Solar System—where they are eventually consumed and destroyed during close approaches to the Sun.[7]

The cloud is thought to encompass two regions: a disc-shaped inner Oort cloud aligned with the solar ecliptic (also called its Hills cloud) and a spherical outer Oort cloud enclosing the entire Solar System. Both regions lie well beyond the heliosphere and are in interstellar space.[4][8] The innermost portion of the Oort cloud is more than a thousand times farther from the Sun than the Kuiper belt, the scattered disc and the detached objects—three nearer reservoirs of trans-Neptunian objects.[9]

The outer limit of the Oort cloud defines the cosmographic boundary of the Solar System. This area is defined by the Sun's Hill sphere, and hence lies at the interface between solar and galactic gravitational dominion.[10] The outer Oort cloud is only loosely bound to the Solar System and its constituents are easily affected by the gravitational pulls of passing stars, the Milky Way itself and the cloud's own microgravity.[11] These forces served to moderate and render more circular the highly eccentric orbits of material ejected from the inner Solar System during its early phases of development. The circular orbits of material in the Oort disc are largely thanks to this galactic gravitational torquing.[12][13] By the same token, galactic interference in the motion of Oort bodies occasionally dislodges comets from their orbits within the cloud, sending them into the inner Solar System.[4] Based on their orbits, most but not all of the short-period comets appear to have come from the Oort disc. Other short-period comets may have originated from the far larger spherical cloud.[4][14]

Astronomers hypothesize that the material presently in the Oort cloud formed much closer to the Sun, in the protoplanetary disc, and was then scattered far into space through the gravitational influence of the giant planets.[4] No direct observation of the Oort cloud is possible with present imaging technology.[15] Nevertheless, the cloud is thought to be the source that replenishes most long-period and Halley-type comets, which are eventually consumed by their close approaches to the Sun after entering the inner Solar System. The cloud may also serve the same function for many of the centaurs and Jupiter-family comets.[14]

Types of distant minor planets

* Centaurs
* Neptune trojans
* Trans-Neptunian objects (TNOs)
* Kuiper belt objects (KBOs)
* Classical KBOs (cubewanos)
* Resonant KBOs
* Plutinos (2:3 resonance)
* Twotinos (1:2 resonance)
* Scattered disc objects (SDOs)
* Resonant SDOs
* Extreme trans-Neptunian object
* Detached objects
* Sednoids
* Oort cloud objects (ICO/OCOs)

* v
* t
* e

## Development of theory

[edit]

By the early 20th century, astronomers had identified two main types of comets: short-period comets (also called ecliptic comets) and long-period comets (also called nearly isotropic comets).[16] Ecliptic comets have relatively small orbits aligned near the ecliptic plane and are not found much farther than the Kuiper cliff around 50 AU from the Sun (the orbit of Neptune averages about 30 AU and 177P/Barnard has aphelion around 48 AU). Long-period comets, on the other hand, travel in very large orbits thousands of AU from the Sun and are isotropically distributed. This means long-period comets appear from every direction in the sky, both above and below the ecliptic plane.[17] The origin of these comets was not well understood, and many long-period comets were initially assumed to be on parabolic trajectories, making them one-time visitors to the Sun from interstellar space.

In 1907, Armin Otto Leuschner suggested that many of the comets then thought to have parabolic orbits in fact moved along extremely large elliptical orbits that would return them to the inner Solar System after long intervals during which they were invisible to Earth-based astronomy.[18] In 1932, the Estonian astronomer Ernst Öpik proposed a reservoir of long-period comets in the form of an orbiting cloud at the outermost edge of the Solar System.[19] Dutch astronomer Jan Oort revived this basic idea in 1950 to resolve a paradox about the origin of comets. The following facts are not easily reconcilable with the highly elliptical orbits in which long-period comets are always found:

* Over millions and billions of years the orbits of Oort cloud comets are unstable. Celestial dynamics will eventually dictate that a comet must be pulled away by a passing star, collide with the Sun or a planet, or be ejected from the Solar System through planetary perturbations.
* Moreover, the volatile composition of comets 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.[20]

Oort reasoned that comets with orbits that closely approach the Sun cannot have been doing so since the condensation of the protoplanetary disc, more than 4.5 billion years ago. Hence long-period comets could not have formed in the current orbits in which they are always discovered and must have been held in an outer reservoir for nearly all of their existence.[20][21][17]

Oort also studied tables of ephemerides for long-period comets and discovered that there is a curious concentration of long-period comets whose farthest retreat from the Sun (their aphelia) cluster around 20,000 AU. This suggested a reservoir at that distance with a spherical, isotropic distribution. He also proposed that the relatively rare comets with orbits of about 10,000 AU probably went through one or more orbits into the inner Solar System and there had their orbits drawn inward by the gravity of the planets.[17]

## Structure and composition

[edit]

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 somewhere between 2,000 and 5,000 AU (0.03 and 0.08 ly)[17] from the Sun to as far out as 50,000 AU (0.79 ly) or even 100,000 to 200,000 AU (1.58 to 3.16 ly).[4][17] The region can be subdivided into a spherical outer Oort cloud with a radius of some 20,000–50,000 AU (0.32–0.79 ly) and a torus-shaped inner Oort cloud with a radius of 2,000–20,000 AU (0.03–0.32 ly).

The inner Oort cloud is sometimes known as the Hills cloud, named for Jack G. Hills, who proposed its existence in 1981.[22] Models predict the inner cloud to be much the denser of the two, having tens or hundreds of times as many cometary nuclei as the outer cloud.[22][23][24] The Hills cloud is thought to be necessary to explain the continued existence of the Oort cloud after billions of years.[25]

Because it lies at the interface between the dominion of Solar and galactic gravitation, the objects comprising the outer Oort cloud are only weakly bound to the Sun. This in turn allows small perturbations from nearby stars or the Milky Way itself to inject long-period (and possibly Halley-type) comets inside the orbit of Neptune.[4] This process ought to have depleted the sparser, outer cloud and yet long-period comets with orbits well above or below the ecliptic continue to be observed. The Hills cloud is thought to be a secondary reservoir of cometary nuclei and the source of replenishment for the tenuous outer cloud as the latter's numbers are gradually depleted through losses to the inner Solar System.[26]

The outer Oort cloud may have trillions of objects larger than 1 km (0.6 mi),[4] and billions with diameters of 20-kilometre (12 mi). This corresponds to an absolute magnitude of more than 11.[27] On this analysis, "neighboring" objects in the outer cloud are separated by a significant fraction of 1 AU, tens of millions of kilometres.[14][28] The outer cloud's total mass is not known, but assuming that Halley's Comet is a suitable proxy for the nuclei composing the outer Oort cloud, their combined mass would be roughly 3×1025 kilograms (6.6×1025 lb), or five Earth masses.[4][29] Formerly the outer cloud was thought to be more massive by two orders of magnitude, containing up to 380 Earth masses,[30] but improved knowledge of the size distribution of long-period comets has led to lower estimates. No estimates of the mass of the inner Oort cloud have been published as of 2023.

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.[31] However, the discovery of the object 1996 PW, an object whose appearance was consistent with a D-type asteroid[32][33] 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.[34] 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,[35] a conclusion also supported by studies of granular size in Oort-cloud comets[36] and by the recent impact study of Jupiter-family comet Tempel 1.[37]

In 2020 researchers discovered an unexpected spiral-shaped pattern in the inner part of the Oort Cloud. This discovery sheds light on how gravity shapes the outer edges of the Solar System.[38]

## Origin

[edit]

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][39]

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.[40] 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.[41][42] A third of the scattered disc's population is likely to end up in the Oort cloud after 2.5 billion years.[43]

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.[44] 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.[45]

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."[46][47] 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.[48][49][50]

## Comets

[edit]

Further information: Halley-type comet and List of Halley-type comets

Further information: Jupiter-family comet and List of periodic comets § List of unnumbered Jupiter-Family comets

Further information: List of centaurs (small Solar System bodies)

Comets are remnants from the formation of the Solar system around 4 billion years ago, stored in two separate areas, the Kuiper belt and the Oort cloud.[51] 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. Very long-period comets, such as C/1999 F1 (Catalina), whose orbits last for millions of years, are thought to originate directly from the outer Oort cloud.[52] Other comets modeled to have come directly from the outer Oort cloud include C/2006 P1 (McNaught), C/2010 X1 (Elenin), Comet ISON, C/2013 A1 (Siding Spring), C/2017 K2, and C/2017 T2 (PANSTARRS). The orbits within the Kuiper belt are relatively stable, 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.[17] Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs.[53][54] These centaurs are then sent farther inward to become the short-period comets.[55]

There are two main types of short-period comets: Jupiter-family comets (with orbits smaller than 5 AU) and Halley-family comets. Halley-family comets, named after Halley's Comet, are distinct because, even though they are short-period comets, they are thought to come from the Oort Cloud rather than the scattered disc.[56][57] 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.[21] 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.[14]

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.[58] No dynamical process is 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.[59] 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.[60] An example of a typical dynamically old comet with an origin in the Oort cloud could be C/2018 F4.[61]

## Sedna and similar objects

[edit]

Main article: Sedna (dwarf planet)

Several observed objects have been proposed as members of the inner Oort cloud.[62] Sedna, first reported in 2004, has a highly eccentric orbit with a perihelion distances of 76AU.[63] 2012 VP113, observed in 2012, has a larger perihelion (closest approach to the Sun) but its aphelion is half of Sedna's.[64][65] Other candidate objects[66] include 2010 GB174[67] and 474640 Alicanto (originally 2004 VN112).[68]

## Tidal effects

[edit]

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.[69] 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 Galactic Center compresses it along the other two axes; these small perturbations can shift orbits in the Oort cloud to bring objects close to the Sun.[70] 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.[17]

Some scholars theorize 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).[71] 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.[72] 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.[73]

## Stellar perturbations and stellar companion hypotheses

[edit]

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.[60] 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 70,000 years ago Scholz's Star passed through the outer Oort cloud (although its low mass and high relative velocity limited its effect).[74][75] During the next 10 million years the known star with the greatest possibility of perturbing the Oort cloud is Gliese 710.[76] This process could also scatter Oort cloud objects out of the ecliptic plane, potentially also explaining its spherical distribution.[76][77]

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.[78] 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.[79][80] Recent scientific analysis no longer supports the idea that extinctions on Earth happen at regular, repeating intervals.[81] Thus, the Nemesis hypothesis is no longer needed to explain current assumptions.[81]

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.[82] 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.[81] In 2014, NASA announced that the WISE survey had ruled out any object as they had defined it.[83]

## Future exploration

[edit]

Artist's impression of the Voyager spacecraft

Space probes have yet to reach the area of the Oort cloud. Voyager 1, the fastest[84] and farthest[85][86] of the interplanetary space probes currently leaving the Solar System, will reach the Oort cloud in about 300 years[8][87] and would take about 30,000 years to pass through it.[88][89] 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 have either already stopped functioning (Pioneer 10, Pioneer 11) or are predicted to also stop functioning before they reach the Oort cloud (Voyager 2, New Horizons).

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.[90]

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.[91] It would monitor distant stars with a photometer, looking for transits up to 10,000 AU away.[91] The observatory was proposed for halo orbiting around L2 with a suggested 5-year mission.[91] It was also suggested that the Kepler space telescope could have been capable of detecting objects in the Oort cloud.[92]

## Further reading

[edit]

* Brasser, Ramon; Morbidelli, Alessandro (2021). "Chronology of Oort Cloud formation". Astronomy & Astrophysics. 650: A44. doi:10.1051/0004-6361/202140096 (inactive 23 March 2025).`{{cite journal}}`: CS1 maint: DOI inactive as of March 2025 (link)
* Fouchard, M.; Rickman, H.; Froeschlé, C.; Valsecchi, G. B. (2023). "What long-period comets tell us about the Oort Cloud". Astronomy & Astrophysics. 671: A36. Bibcode:2023A&A...676A.104F. doi:10.1051/0004-6361/202243728.
* Hands, T. O.; Dehnen, W.; Gration, A. (2021). "Formation of extrasolar Oort clouds and the origin of interstellar objects". Astronomy & Astrophysics. 647: A96. arXiv:2011.08257. doi:10.1051/0004-6361/202038888.
* Batygin, Konstantin; Raush, Dennis (2024). "Formation of the inner Oort cloud in the presence of an early solar binary". Monthly Notices of the Royal Astronomical Society: Letters. 533 (1): L43 – L47. arXiv:2305.00999. doi:10.1093/mnrasl/slad107.

## See also

[edit]

* Heliosphere
* Interstellar object
* List of possible dwarf planets
* List of trans-Neptunian objects
* Planets beyond Neptune
* Scattered disc
* Tyche (hypothetical planet)
* Nemesis (hypothetical star)
* Hills cloud

## References

[edit]

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27. ^ Absolute magnitude is a measure of how bright an object would be if it were 1 au from the Sun and Earth; as opposed to apparent magnitude, which measures how bright an object appears from Earth. Because all measurements of absolute magnitude assume the same distance, absolute magnitude is in effect a measurement of an object's brightness. The lower an object's absolute magnitude, the brighter it is.
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* Oort Cloud Profile Archived 2015-11-10 at the Wayback Machine 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.
* Oort, Jan H. (1950). "The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin". Bulletin of the Astronomical Institutes of the Netherlands. 11: 91–110\. Bibcode:1950BAN....11...91O.

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Consensus|

* Ceres
* Geology
* Atmosphere
* Orcus
* Moon
* Pluto
* Geology
* Atmosphere
* Moons
* Haumea
* Moons
* Ring
* Makemake
* Moon
* Quaoar
* Moon
* Rings
* Eris
* Moon
* Gonggong
* Moon
* Sedna

Candidate
(for TNOs, D+1σ ≥ 700 km
or H ≤ 4.2)|

| Asteroids|

* Hygiea
* Interamnia

|

Plutinos|

* Ixion

Cubewanos|

* Salacia
* Varda
* 2002 AW197
* 2002 MS4
* 2004 GV9
* 2005 RN43

Other KBOs|

* 2013 FZ27

Scattered disc
objects|

* 2010 KZ39
* 2010 RE64
* 2010 RF43
* 2010 JO179
* 2013 FY27
* 2014 EZ51
* 2014 UZ224
* 2015 KH162
* 2015 RR245
* 2017 OF201
* 2018 AG37
* 2018 VG18
* 2021 DR15
* 2021 LL37

Detached objects|

* 2007 JJ43
* 2008 ST291

Sednoids|

* 2012 VP113

* Category

* 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/2025 F2 (SWAN)
* 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)

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
* 489P/Denning

|

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
* D/1978 R1 (Haneda–Campos)

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/1739 K1 (Zanotti)
* 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/1846 J1 (Brorsen)
* C/1847 T1 (Miss Mitchell's Comet)
* C/1852 K1 (Chacornac)
* C/1853 G1 (Schweizer)
* C/1858 L1 (Comet Donati)
* C/1861 G1 (Comet Thatcher)
* C/1861 J1 (Great Comet of 1861)
* C/1862 N1 (Schmidt)
* C/1864 N1 (Tempel)
* 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/1893 U1 (Brooks)
* C/1901 G1 (Great Comet of 1901)
* C/1907 G1 (Grigg–Mellish)
* C/1910 A1 (Great January Comet of 1910)
* C/1911 N1 (Kiess)
* C/1911 O1 (Brooks)
* C/1911 S3 (Beljawsky)
* C/1915 C1 (Mellish)
* C/1917 F1 (Mellish)
* C/1927 X1 (Skjellerup–Maristany)
* C/1931 P1 (Ryves)
* C/1936 O1 (Kaho–Kozik–Lis)
* C/1939 H1 (Jurlof–Achmarof–Hassel)
* C/1941 B2 (de Kock-Paraskevopoulos)
* C/1947 X1 (Southern Comet)
* C/1948 L1 (Honda–Bernasconi)
* C/1948 V1 (Eclipse)
* C/1956 R1 (Arend–Roland)
* C/1957 P1 (Mrkos)
* C/1961 O1 (Wilson-Hubbard)
* C/1961 R1 (Humason)
* C/1961 T1 (Seki)
* 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)
* C/1969 Y1 (Bennett)
* C/1970 K1 (White–Ortiz–Bolelli)
* C/1973 E1 (Kohoutek)
* C/1975 T2 (Suzuki–Saigusa–Mori)
* C/1975 V1 (West)
* C/1979 Y1 (Bradfield)
* C/1980 E1 (Bowell)
* C/1983 H1 (IRAS–Araki–Alcock)
* C/1983 J1 (Sugano–Saigusa–Fujikawa)
* 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/2014 UN271 (Bernardinelli–Bernstein)
* 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)
* C/2024 G3 (ATLAS)
* C/2024 S1 (ATLAS)

After 1910
(by name)|

* Aarseth-Brewington
* Arend–Roland
* ATLAS
* C/2019 Y4 (ATLAS)
* C/2024 G3 (ATLAS)
* C/2024 S1 (ATLAS)
* Austin
* Beljawsky
* Bennett
* Bernardinelli–Bernstein
* Boattini
* Borisov
* Bowell
* Bradfield
* C/1979 Y1
* C/2004 F4
* Brooks
* Catalina
* C/1999 F1
* C/2013 US10
* de Kock–Paraskevopoulos
* Eclipse
* Elenin
* Hale-Bopp
* Honda–Bernasconi
* Humason
* Hyakutake
* Ikeya
* C/1963 A1
* C/1964 N1
* Ikeya-Seki
* IRAS–Araki–Alcock
* ISON
* Iwamoto
* Jacques
* Johnson
* Jurlof–Achmarof–Hassel
* Kaho–Kozik–Lis
* Kiess
* 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
* John E. Mellish
* C/1915 C1 (Mellish)
* C/1917 F1 (Mellish)
* 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
* Seki–Lines
* Siding Spring
* C/2007 Q3
* C/2013 A1
* Skjellerup–Maristany
* Skorichenko–George
* SOHO
* Southern
* Spacewatch–Rabinowitz
* Stonehouse
* Sugano–Saigusa–Fujikawa
* Suzuki–Saigusa–Mori
* SWAN
* C/2006 M4
* C/2012 E2
* C/2020 F8
* Tago-Sato-Kosaka
* Tsuchinshan–ATLAS
* West
* White–Ortiz–Bolelli
* Wilson–Hubbard
* Yi–SWAN
* Zhu–Balam
* ZTF

* Category

Portals:

* Astronomy
* Stars
* Spaceflight
* Outer space
* Solar system

Authority control databases

International|

* VIAF
* FAST

National|

* United States
* Israel

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