Classical_Kuiper_belt_object

# Classical Kuiper belt object  **Microsim — three.js (Wikitube framework):** *The Kuiper belt in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=kuiper&embed=1" data-title="The Kuiper belt in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=kuiper`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: under show, choose small bodies to leave the belt's sampled points and the plutino ring at 39.4 AU on their own; drag to an edge-on view and compare the thin, flat core of the cloud with the few points that stray far above and below it; then set show back to everything and the speed to 100 years/s and watch Neptune lap in about 1.6 seconds, a pace a classical object near 44 AU would take almost twice as long to match.* A **classical Kuiper belt object**, also called a **cubewano**, is a [[Kuiper_belt|Kuiper belt]] object on a low-eccentricity orbit beyond [[Neptune]] that is not held in an orbital [[Resonance|resonance]] with that planet.[^jewitt-classical][^elliot2005] Classical objects have semi-major axes of roughly 40–50 [[Astronomical_unit|AU]] and, unlike [[Pluto]] and many other [[Plutino|plutinos]], never approach Neptune's orbit.[^jewitt2006] The nickname comes from 1992 QB1, now 15760 Albion, the first [[Trans-Neptunian_object|trans-Neptunian object]] found after Pluto and [[Charon_(moon)|Charon]]: later objects like it were called "QB1-os".[^jewitt-classical] Most researchers simply say "classical". Classical objects come in two overlapping populations. A "cold" population on nearly circular, nearly flat orbits is uniformly red, rich in binaries and probably formed where it now orbits; a "hot" population on more inclined and eccentric orbits has a wider range of colours and was probably scattered outward from closer to the Sun.[^levison2003][^noll2008][^peixinho2008] Known members include Albion, the dwarf planet [[Makemake]], [[Quaoar]], 20000 Varuna and 486958 Arrokoth, the only one yet visited by a spacecraft.[^mpc2010][^jhuapl2019] The explorer at the top of this page is locked on the Kuiper belt. Its cloud of points, drawn from 30 to 50 AU, is ILLUSTRATIVE, a sample standing in for the whole belt; the classical region lies in its outer part, beyond the ring that marks the plutinos at 39.4 AU.[^jpl-t1] ## Orbits: 'hot' and 'cold' populations Most classical objects orbit between two resonances with Neptune: the 2:3 resonance, occupied by the plutinos, and the 1:2 resonance. By [[Kepler's_laws_of_planetary_motion|Kepler's third law]] a period 3/2 or 2 times Neptune's corresponds to a semi-major axis 1.5^(2/3) or 2^(2/3) times Neptune's 30.07 AU, that is, 39.4 or 47.7 AU (derived).[^jpl-t1] In between, orbits can remain nearly unchanged for billions of years. Quaoar is typical, with a semi-major axis of 43.2 AU, an eccentricity of 0.035 and an inclination of 8°; its distance from the [[Sun]] varies only between 41.6 and 44.7 AU.[^jpl-sbdb] A plutino such as Pluto, by contrast, swings in to within Neptune's orbit. Most classical objects belong to the cold population, with inclinations below about 5°, near-circular orbits and semi-major axes of about 42–47 AU; a smaller hot population has more inclined and eccentric orbits.[^jewitt2006] "Hot" and "cold" say nothing about temperature. They borrow the language of gases, in which hotter molecules move faster relative to one another: bodies on more inclined and eccentric orbits meet at higher relative speeds.[^levison2003] The Deep Ecliptic Survey described the two as a "core" with inclinations centred near 4.6° and a "halo" whose inclinations extend beyond 30°.[^elliot2005] The two populations are thought to have different histories. In models of Neptune's outward migration, the hot objects formed closer to the Sun and were carried outward and stirred up by the planet, whereas the cold objects formed in place and were disturbed only lightly.[^levison2003] ### Distribution More than two-thirds of the classical objects have inclinations under 5° and eccentricities under 0.1, and their semi-major axes cluster in the middle of the region. Near the limiting resonances, smaller objects have either been captured into resonance or had their orbits altered by Neptune.[^jewitt2006] The resulting picture is a well-defined band outside Neptune's orbit. Plutinos, in contrast, have more evenly spread orbits, with moderate eccentricities of about 0.15–0.2 and inclinations commonly 5–10°, and many approach or cross Neptune's orbit.[^jewitt-plutino] High-inclination hot classicals stand out clearly, since plutino inclinations generally stay under 20°; how the hot population acquired such steep orbits is still debated.[^jewitt-plutino][^levison2003] The distribution also has an outer edge. Surveys noted a lack of low-inclination objects beyond about 47–49 AU as early as 1998, and Chadwick Trujillo and Michael Brown showed with more data in 2001 that the drop is real rather than an observational bias.[^trujillo2001] This edge, close to the 1:2 resonance, bounds the classical belt on the outside. ## Cold and hot populations: physical characteristics The populations differ physically as well as dynamically. By 2002 surveys had shown that low-inclination classicals are uniformly red while high-inclination ones range from grey to red.[^doressoundiram2002] A larger sample analysed by Nuno Peixinho, Pedro Lacerda and David Jewitt in 2008 placed the colour break at an inclination of about 12°, not 5°, and confirmed the contrast between the homogeneous red cold objects and the bluer hot ones.[^peixinho2008] Binaries differ too. On low-inclination orbits, binaries are common and usually made of two components of similar brightness; on high-inclination orbits they are rarer and their components more unequal.[^noll2008] A widely separated, loosely bound binary would be split by a close encounter with Neptune, so the survival of many such pairs in the cold population supports the idea that it was never strongly disturbed.[^parker2010] Taken together, colours and binaries indicate at least two populations with separate origins that now share the same region.[^noll2008] Size may follow the same division. The largest classicals, such as Makemake and Quaoar, belong to the hot population, while the cold population lacks very large bodies.[^levison2001] ## Toward a formal definition No official definition of "classical" or "cubewano" exists. In practice the terms mean Kuiper belt objects free from significant perturbation by Neptune, excluding those in resonance ([[Resonant_trans-Neptunian_object|resonant trans-Neptunian objects]]).[^jewitt-classical] Catalogues apply this differently. The Minor Planet Center lists Makemake as a classical object, while the Deep Ecliptic Survey (DES) classes it as "scattered-near", an object possibly scattered by Neptune.[^mpc2010][^elliot2005] Makemake's current orbit, with an eccentricity of 0.16 and an inclination of 29°, shows why the call is borderline.[^jpl-sbdb] Haumea, provisionally listed as classical in 2006, was later found to be on a resonant orbit.[^mpc2006][^mpc2010] Traditional usage relies on the semi-major axis, taking objects between the 2:3 and 1:2 resonances, about 39.4–47.8 AU, and excluding those resonances and the weaker ones in between.[^jewitt2006] The boundary with the [[Scattered_disc|scattered disc]] remains blurred. A simple orbital cut gives a sense of the population: on 18 September 2026 the JPL Small-Body Database held 1,176 objects with perihelion beyond 40 AU and aphelion inside 48 AU.[^jpl-sbdb] ### DES classification The DES, described by James Elliot and colleagues in 2005, uses averaged orbital elements from a forward integration.[^elliot2005] An object is classical if it is not resonant, its average Tisserand parameter with respect to Neptune exceeds 3, and its average eccentricity is below 0.2. Informally, this picks out objects that have never crossed Neptune's orbit.[^elliot2005] ### SSBN07 classification Brett Gladman, Brian Marsden and Christa Van Laerhoven, writing in *The Solar System Beyond Neptune* (2008), replace the Tisserand criterion with a 10-million-year integration.[^gladman2008] Classical objects are those that are non-resonant, have semi-major axes between Neptune's 30.1 AU and 2,000 AU (excluding [[Centaur_(small_Solar_System_body)|centaurs]] and the inner [[Oort_cloud|Oort cloud]]), are not currently being scattered by Neptune, and have eccentricities below 0.24, to exclude [[Detached_object|detached objects]]. The scheme extends the class inward of the 2:3 resonance, as the inner classical belt, and outward of the 1:2 resonance, as the outer classical belt, reserving "main classical belt" for the region between.[^gladman2008] ## Families A collisional family is a group of bodies that share similar orbits because they are fragments of one parent. Collisions among Kuiper belt objects are slow and rare today, so a family records an unusual event, and its fragments stay close together in orbital elements for long periods. The first identified in the Kuiper belt is the [[Haumea]] family: Haumea, its moons and several smaller bodies, all with similar orbits and similar surfaces.[^brown2007] The family sits among the hot classical objects; Haumea itself has a semi-major axis of 43.1 AU, an eccentricity of 0.19 and an inclination of 28°.[^jpl-sbdb] Haumea spins once every 3.9 hours and is strongly elongated, properties consistent with a violent past.[^rabinowitz2006] Family members show neutral colours and deep [[Water|water]]-ice absorptions at 1.5 and 2.0 μm in their infrared spectra, and little of the red organic material common on other Kuiper belt objects.[^pinilla2009][^pinilla2007] Their shared orbits and fresh icy surfaces point to a single collision that broke the icy mantle off a differentiated parent.[^brown2007] Other possible families in the classical belt have been proposed, from similarities in orbits and surfaces, but none is as secure.[^chiang2002][^delafuente2018] ## Exploration Before the belt was discovered, both Voyager spacecraft crossed the region without being aimed at any object there; no one then knew of a target to aim for, and their trajectories had been set by their planetary encounters.[^stern2018] New Horizons, after flying past Pluto in July 2015, became the first mission to visit a classical object. Its extended-mission target had to be found first: ground-based telescopes could not locate a reachable object, and it took a dedicated search with the Hubble Space Telescope in 2014 to find candidates along the spacecraft's path.[^jhuapl2014] The object now called Arrokoth was selected in August 2015, and NASA approved the extended mission on 1 July 2016.[^mckinnon2015][^nasa2016] On 1 January 2019 it passed about 3,500 km from 486958 Arrokoth, a small cold classical with a semi-major axis of 44.1 AU and an inclination of only 2.5°.[^lakdawalla2018][^jhuapl2019][^jpl-sbdb] Arrokoth proved to be a contact binary about 32 km long, with two flattened lobes joined at a narrow neck.[^corum2019] ## List Among the many classical objects, the following are well studied: 15760 Albion, the prototype; 20000 Varuna and 50000 Quaoar, each considered the largest trans-Neptunian object known at the time of its discovery; the dwarf planet 136472 Makemake; 19521 Chaos, 58534 Logos, 53311 Deucalion, 66652 Borasisi, 88611 Teharonhiawako, 55565 Aya and 55637 Uni; the binary 79360 Sila–Nunam; 120347 Salacia; and 486958 Arrokoth.[^mpc2010][^jhuapl2019] Their orbits illustrate the range of the class: Albion has a = 44.1 AU, e = 0.07 and i = 2.2°, a cold orbit, while Varuna, at a = 43.2 AU, is inclined 17°, placing it in the hot population.[^jpl-sbdb] A cold object at 44 AU takes about 44^1.5 ≈ 292 years to orbit the Sun, 1.77 of Neptune's orbital periods (derived). ## See also - [[Kuiper_belt]] · [[Trans-Neptunian_object]] - [[Plutino]] · [[Resonant_trans-Neptunian_object]] - [[Scattered_disc]] · [[Detached_object]] - [[Dwarf_planet]] ## Footnotes Derived values: resonance distances follow from Kepler's third law with Neptune's semi-major axis of 30.07 AU (JPL Table 1). The period of an object at 44 AU is 44^1.5 ≈ 292 years; Neptune's is 30.07^1.5 ≈ 165 years. Orbital elements from the JPL Small-Body Database are osculating values at the database epoch; database counts change as new objects are found. ## References [^jewitt-classical]: Jewitt, D. "Classical Kuiper belt objects". UCLA. http://www2.ess.ucla.edu/~jewitt/kb/def_classical.html [^elliot2005]: Elliot, J. L.; Kern, S. D.; Clancy, K. B.; et al. (2005). "The Deep Ecliptic Survey: a search for Kuiper belt objects and Centaurs. II. Dynamical classification, the Kuiper belt plane, and the core population". *The Astronomical Journal* 129: 1117–1162. https://doi.org/10.1086/427395 [^jewitt2006]: Jewitt, D.; Delsanti, A. (2006). "The Solar System beyond the planets". In *Solar System Update*. Springer-Praxis. ISBN 978-3-540-26056-1. http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf [^levison2003]: Levison, H. F.; Morbidelli, A. (2003). "The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration". *Nature* 426: 419–421. https://doi.org/10.1038/nature02120 [^noll2008]: Noll, K. S.; Grundy, W. M.; Stephens, D. C.; Levison, H. F.; Kern, S. D. (2008). "Evidence for two populations of classical transneptunian objects: the strong inclination dependence of classical binaries". *Icarus* 194: 758–768. https://doi.org/10.1016/j.icarus.2007.10.022 [^peixinho2008]: Peixinho, N.; Lacerda, P.; Jewitt, D. (2008). "Color–inclination relation of the classical Kuiper belt objects". *The Astronomical Journal* 136: 1837–1845. https://doi.org/10.1088/0004-6256/136/5/1837 [^mpc2010]: Marsden, B. G. (30 January 2010). "MPEC 2010-B62: Distant minor planets". Minor Planet Center. http://www.minorplanetcenter.org/mpec/K10/K10B62.html [^mpc2006]: Minor Planet Center (12 December 2006). "MPEC 2006-X45: Distant minor planets". https://minorplanetcenter.net//mpec/K06/K06X45.html [^jhuapl2019]: Johns Hopkins University Applied Physics Laboratory (1 January 2019). "New Horizons successfully explores Ultima Thule". http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20190101 [^levison2001]: Levison, H. F.; Stern, S. A. (2001). "On the size dependence of the inclination distribution of the main Kuiper belt". *The Astronomical Journal* 121: 1730–1735. https://doi.org/10.1086/319420 [^parker2010]: Parker, A. H.; Kavelaars, J. J. (2010). "Destruction of binary minor planets during Neptune scattering". *The Astrophysical Journal Letters* 722: L204–L208. https://doi.org/10.1088/2041-8205/722/2/L204 [^rabinowitz2006]: Rabinowitz, D. L.; Barkume, K.; Brown, M. E.; et al. (2006). "Photometric observations constraining the size, shape, and albedo of 2003 EL61, a rapidly rotating, Pluto-sized object in the Kuiper belt". *The Astrophysical Journal* 639: 1238–1251. https://doi.org/10.1086/499575 [^jhuapl2014]: Johns Hopkins University Applied Physics Laboratory (15 October 2014). "NASA's Hubble telescope finds potential Kuiper belt targets for New Horizons Pluto mission" (press release). http://www.jhuapl.edu/newscenter/pressreleases/2014/141015_2.asp [^mckinnon2015]: McKinnon, M. (28 August 2015). "New Horizons locks onto next target: let's explore the Kuiper belt!". *Gizmodo*. http://space.gizmodo.com/new-horizons-locks-onto-next-target-lets-explore-the-k-1727298103 [^nasa2016]: Brown, D.; Cantillo, L. (1 July 2016). "New Horizons receives mission extension to Kuiper belt, Dawn to remain at Ceres". NASA. https://www.nasa.gov/feature/new-horizons-receives-mission-extension-to-kuiper-belt-dawn-to-remain-at-ceres [^jpl-t1]: JPL Solar System Dynamics. "Approximate Positions of the Planets", Table 1. https://ssd.jpl.nasa.gov/planets/approx_pos.html [^jpl-sbdb]: JPL Solar System Dynamics. "Small-Body Database" (elements of 136108 Haumea, 15760 Albion, 20000 Varuna, 50000 Quaoar, 136472 Makemake and 486958 Arrokoth; query of objects with q > 40 AU and Q < 48 AU), fetched 2026-09-18. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html [^jewitt-plutino]: Jewitt, D. (2004). "The plutinos". University of Hawaii. http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html [^trujillo2001]: Trujillo, C. A.; Brown, M. E. (2001). "The radial distribution of the Kuiper belt". *The Astrophysical Journal* 554: L95–L98. https://doi.org/10.1086/320917 [^doressoundiram2002]: Doressoundiram, A.; Peixinho, N.; de Bergh, C.; et al. (2002). "The color distribution in the Edgeworth–Kuiper belt". *The Astronomical Journal* 124: 2279–2296. https://doi.org/10.1086/342447 [^gladman2008]: Gladman, B.; Marsden, B. G.; Van Laerhoven, C. (2008). "Nomenclature in the outer Solar System". In *The Solar System Beyond Neptune*. University of Arizona Press, pp. 43–57. ISBN 978-0-8165-2755-7. http://www.lpi.usra.edu/books/ssbn2008/7002.pdf [^brown2007]: Brown, M. E.; Barkume, K. M.; Ragozzine, D.; Schaller, E. L. (2007). "A collisional family of icy objects in the Kuiper belt". *Nature* 446: 294–296. https://doi.org/10.1038/nature05619 [^pinilla2009]: Pinilla-Alonso, N.; Brunetto, R.; Licandro, J.; Gil-Hutton, R.; Roush, T. L.; Strazzulla, G. (2009). "The surface of (136108) Haumea (2003 EL61), the largest carbon-depleted object in the trans-Neptunian belt". *Astronomy and Astrophysics* 496: 547–556. https://doi.org/10.1051/0004-6361/200809733 [^pinilla2007]: Pinilla-Alonso, N.; Licandro, J.; Gil-Hutton, R.; Brunetto, R. (2007). "The water ice rich surface of (145453) 2005 RR43: a case for a carbon-depleted population of TNOs?". *Astronomy and Astrophysics* 468: L25–L28. https://doi.org/10.1051/0004-6361:20077294 [^chiang2002]: Chiang, E. I. (2002). "A collisional family in the classical Kuiper belt". *The Astrophysical Journal* 573: L65–L68. https://doi.org/10.1086/342089 [^delafuente2018]: de la Fuente Marcos, C.; de la Fuente Marcos, R. (2018). "Dynamically correlated minor bodies in the outer Solar system". *Monthly Notices of the Royal Astronomical Society* 474: 838–846. https://doi.org/10.1093/mnras/stx2765 [^stern2018]: Stern, A. (28 February 2018). "The PI's perspective: why didn't Voyager explore the Kuiper belt?". New Horizons, JHUAPL. https://pluto.jhuapl.edu/News-Center/PI-Perspectives.php?page=piPerspective_02_28_2018 [^lakdawalla2018]: Lakdawalla, E. (24 January 2018). "New Horizons prepares for encounter with 2014 MU69". The Planetary Society. https://www.planetary.org/blogs/emily-lakdawalla/2018/0124-new-horizons-prepares-for-2014mu69.html [^corum2019]: Corum, J. (10 February 2019). "New Horizons glimpses the flattened shape of Ultima Thule". *The New York Times*. https://www.nytimes.com/interactive/2018/12/31/science/new-horizons-ultima-thule-flyby.html ## External links - David Jewitt: classical Kuiper belt objects (UCLA). http://www2.ess.ucla.edu/~jewitt/kb/def_classical.html - Minor Planet Center: list of trans-Neptunian objects. https://minorplanetcenter.net/iau/lists/TNOs.html - JPL Small-Body Database. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html - New Horizons mission (JHUAPL). https://pluto.jhuapl.edu/ ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Classical_Kuiper_belt_object) : [Wikitube](https://en.wikitube.io/wiki/Classical_Kuiper_belt_object) · pinned revision [1372864597](https://en.wikipedia.org/w/index.php?oldid=1372864597) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-066 · explorer state `?obj=kuiper`.*