Classical Kuiper belt object

{{Short description|Kuiper belt object, not controlled by an orbital resonance with Neptune}}

File:UltimaThule_CA06_color_20190516.png, the first classical Kuiper belt object visited by a spacecraft.]]

File:Cubewanos.png (blue) and Pluto (pink)]]

A classical Kuiper belt object, also called a cubewano ({{IPAc-en|ˌ|k|juː|b|iː|ˈ|w|ʌ|n|oʊ}} "QB1-o"),{{efn|Somewhat old-fashioned, but "cubewano" is still used by the Minor Planet Center for their list of Distant Minor Planets.{{cite web |url=http://www.minorplanetcenter.org/mpec/K10/K10S44.html |title=Distant Minor Planets}}}} is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axes in the 40–50 AU range and, unlike Pluto, do not cross Neptune's orbit. That is, they have low-eccentricity and sometimes low-inclination orbits like the classical planets.

The name "cubewano" derives from the first trans-Neptunian object (TNO) found after Pluto and Charon: 15760 Albion, which until January 2018 had only the provisional designation (15760) {{mp|1992 QB|1}}.{{cite web |url=http://www2.ess.ucla.edu/~jewitt/kb/def_classical.html |title=Classical Kuiper Belt Objects |author-link=David Jewitt |first=David |last=Jewitt |publisher=UCLA |access-date=1 July 2013}} Similar objects found later were often called "QB1-os", or "cubewanos", after this object, though the term "classical" is much more frequently used in the scientific literature.

Objects identified as cubewanos include:

15760 Albion (aka {{mp|1992 QB|1}} and gave rise to term 'Cubewano')
136472 Makemake, the largest known cubewano{{Citation needed|reason=This conflicts with the main page for Makemake, which claims that Makemake is the second largest cubewano.|date=January 2024}} and a dwarf planet
50000 Quaoar and 20000 Varuna, each considered the largest TNO at the time of discovery
19521 Chaos, 58534 Logos, 53311 Deucalion, 66652 Borasisi, 88611 Teharonhiawako
{{mpl|(33001) 1997 CU|29}}, {{mpl|(55636) 2002 TX|300}}, {{mpl|(55565) 2002 AW|197}}, {{mpl|(55637) 2002 UX|25}}
486958 Arrokoth

136108 Haumea was provisionally listed as a cubewano by the Minor Planet Center in 2006,{{cite web |date=2006-12-12 |title=MPEC 2006-X45: Distant Minor Planets |url=https://minorplanetcenter.net//mpec/K06/K06X45.html |access-date=2008-10-03 |df=dmy-all |publisher=IAU Minor Planet Center & Tamkin Foundation Computer Network}} but was later found to be in a resonant orbit.

{{cite web |date=2010-01-30 |title=MPEC 2010-B62: Distant Minor Planets (2010 FEB. 13.0 TT) |author=Brian G. Marsden |department=IAU Minor Planet Center |publisher=Harvard-Smithsonian Center for Astrophysics |url=http://www.minorplanetcenter.org/mpec/K10/K10B62.html |archive-url=https://archive.today/20120904012403/http://www.minorplanetcenter.org/mpec/K10/K10B62.html |url-status=dead |archive-date=2012-09-04 |df=dmy-all |access-date=2010-07-26}}

File:TheKuiperBelt 55AU Classical.svg and inclination of cubewanos (blue) compared to resonant TNOs (red).]]

There are two basic dynamical classes of classical Kuiper-belt bodies: those with relatively unperturbed ('cold') orbits, and those with markedly perturbed ('hot') orbits.

Most cubewanos are found between the 2:3 orbital resonance with Neptune (populated by plutinos) and the 1:2 resonance. 50000 Quaoar, for example, has a near-circular orbit close to the ecliptic. Plutinos, on the other hand, have more eccentric orbits bringing some of them closer to the Sun than Neptune.

The majority of classical objects, the so-called cold population, have low inclinations (< 5°) and near-circular orbits, lying between 42 and 47 AU. A smaller population (the hot population) is characterised by highly inclined, more eccentric orbits.{{cite book |last1=Jewitt |first1=D. |author1-link=David Jewitt |last2=Delsanti |first2=A. |year=2006 |chapter=The Solar System Beyond The Planets |title=Solar System Update : Topical and Timely Reviews in Solar System Sciences |publisher=Springer-Praxis |chapter-url=http://www2.ess.ucla.edu/~jewitt/papers/2006/DJ06.pdf |isbn=978-3-540-26056-1 |url=http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |access-date=March 2, 2006 |archive-url=https://web.archive.org/web/20070129151907/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |archive-date=2007-01-29 |df=dmy-all |url-status=dead}}) The terms 'hot' and 'cold' has nothing to do with surface or internal temperatures, but rather refer to the orbits of the objects, by analogy to molecules in a gas, which increase their relative velocity as they heat up.{{cite journal |last1=Levison |first1=Harold F. |last2=Morbidelli |first2=Alessandro |date=2003 |title=The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration |journal=Nature |volume=426 |issue=6965 |pages=419–421 |doi=10.1038/nature02120 |pmid=14647375 |bibcode=2003Natur.426..419L|s2cid=4395099 }}

The Deep Ecliptic Survey reports the distributions of the two populations; one with the inclination centered at 4.6° (named Core) and another with inclinations extending beyond 30° (Halo).

{{cite journal |author=J. L. Elliot |year=2006 |title=The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population |journal=Astronomical Journal |volume=129 |issue=2 |pages=1117–1162 |bibcode=2005AJ....129.1117E |doi=10.1086/427395 |display-authors=etal|doi-access=free }} ({{cite web |url=http://alpaca.as.arizona.edu/~trilling/des2.pdf |title=Preprint |archive-url=https://web.archive.org/web/20060823112517/http://alpaca.as.arizona.edu/~trilling/des2.pdf |archive-date=2006-08-23 |df=dmy-all}})

= Distribution =

The vast majority of KBOs (more than two-thirds) have inclinations of less than 5° and eccentricities of less than 0.1 . Their semi-major axes show a preference for the middle of the main belt; arguably, smaller objects close to the limiting resonances have been either captured into resonance or have their orbits modified by Neptune.

The 'hot' and 'cold' populations are strikingly different: more than 30% of all cubewanos are in low inclination, near-circular orbits. The parameters of the plutinos’ orbits are more evenly distributed, with a local maximum in moderate eccentricities in 0.15–0.2 range, and low inclinations 5–10°.

See also the comparison with scattered disk objects.

Cubewanos form a clear 'belt' outside Neptune's orbit, whereas the plutinos approach, or even cross Neptune's orbit. When orbital inclinations are compared, 'hot' cubewanos can be easily distinguished by their higher inclinations, as the plutinos typically keep orbits <20°. The high inclination of 'hot' cubewanos has not been explained.

{{cite web |last=Jewitt |first=D. |author-link=David Jewitt |year=2004 |title=Plutino |url=http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html |url-status=dead |archive-url=https://web.archive.org/web/20070419234021/http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html |archive-date=2007-04-19 |df=dmy-all}}

{{multiple image

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|image1= KBOs and resonances.png

|image2=TheKuiperBelt Projections 55AU Classical Plutinos.svg

|footer=Left: TNO distribution of cubewanos (blue), resonant TNOs (red), SDOs (grey) and sednoids (yellow). Right: Comparison of the aligned orbits (polar and ecliptic view) of cubewanos, plutinos, and Neptune (yellow).

}}

Cold and hot populations: physical characteristics

In addition to the distinct orbital characteristics, the two populations display different physical characteristics.

The difference in colour between the red cold population, such as 486958 Arrokoth, and more heterogeneous hot population was observed as early as in 2002.

{{cite journal |author1=A. Doressoundiram |author2=N. Peixinho |author3=C. de Bergh |author4=S. Fornasier |author5=P. Thebault |author6=M. A. Barucci |author7=C. Veillet |title=The Color Distribution in the Edgeworth-Kuiper Belt |journal=The Astronomical Journal |date=October 2002 |arxiv=astro-ph/0206468 |bibcode=2002AJ....124.2279D |doi=10.1086/342447 |volume=124 |issue=4 |page=2279|s2cid=30565926 }}

Recent studies, based on a larger data set, indicate the cut-off inclination of 12° (instead of 5°) between the cold and hot populations and confirm the distinction between the homogenous red cold population and the bluish hot population.

{{cite journal |first1=Nuno |last1=Peixinho |first2=Pedro |last2=Lacerda |first3=David |last3=Jewitt |author3-link=David Jewitt |title=Color-inclination relation of the classical Kuiper belt objects |journal=The Astronomical Journal |date=August 2008 |arxiv=0808.3025 |bibcode=2008AJ....136.1837P |doi=10.1088/0004-6256/136/5/1837 |volume=136 |issue=5 |pages=1837|s2cid=16473299 }}

Another difference between the low-inclination (cold) and high-inclination (hot) classical objects is the observed number of binary objects. Binaries are quite common on low-inclination orbits and are typically similar-brightness systems. Binaries are less common on high-inclination orbits and their components typically differ in brightness. This correlation, together with the differences in colour, support further the suggestion that the currently observed classical objects belong to at least two different overlapping populations, with different physical properties and orbital history.

{{cite journal |author1=K. Noll |author2=W. Grundy |author3=D. Stephens |author4=H. Levison |author5=S. Kern |title=Evidence for two populations of classical transneptunian objects: The strong inclination dependence of classical binaries |journal=Icarus |date=April 2008 |arxiv=0711.1545 |bibcode=2008Icar..194..758N |doi=10.1016/j.icarus.2007.10.022 |volume=194 |issue=2 |pages=758|s2cid=336950 }}

Toward a formal definition

There is no official definition of 'cubewano' or 'classical KBO'. However, the terms are normally used to refer to objects free from significant perturbation from Neptune, thereby excluding KBOs in orbital resonance with Neptune (resonant trans-Neptunian objects). The Minor Planet Center (MPC) and the Deep Ecliptic Survey (DES) do not list cubewanos (classical objects) using the same criteria. Many TNOs classified as cubewanos by the MPC, such as dwarf planet Makemake, are classified as ScatNear (possibly scattered by Neptune) by the DES. {{mpl|(119951) 2002 KX|14}} may be an inner cubewano near the plutinos. Furthermore, there is evidence that the Kuiper belt has an 'edge', in that an apparent lack of low-inclination objects beyond 47–49 AU was suspected as early as 1998 and shown with more data in 2001.

{{cite journal |last1=Trujillo |first1=Chadwick A. |last2=Brown |first2=Michael E. |year=2001 |title=The Radial Distribution of the Kuiper Belt |url=http://www.gps.caltech.edu/~chad/publications/2001-trujillo-brown.pdf |journal=The Astrophysical Journal |volume=554 |issue=1 |pages=L95–L98 |bibcode=2001ApJ...554L..95T |doi=10.1086/320917 |s2cid=7982844 |url-status=dead |archive-url=https://web.archive.org/web/20060919003142/http://www.gps.caltech.edu/~chad/publications/2001-trujillo-brown.pdf |archive-date=2006-09-19 |df=dmy-all}} Consequently, the traditional usage of the terms is based on the orbit's semi-major axis, and includes objects situated between the 2:3 and 1:2 resonances, that is between 39.4 and 47.8 AU (with exclusion of these resonances and the minor ones in-between).

These definitions lack precision: in particular the boundary between the classical objects and the scattered disk remains blurred. {{Asof|2023}}, there are 870 objects with perihelion (q) > 40 AU and aphelion (Q) < 48 AU.

= DES classification =

Introduced by the report from the Deep Ecliptic Survey by J. L. Elliott et al. in 2005 uses formal criteria based on the mean orbital parameters. Put informally, the definition includes the objects that have never crossed the orbit of Neptune. According to this definition, an object qualifies as a classical KBO if:

it is not resonant
its average Tisserand's parameter with respect to Neptune exceeds 3
its average eccentricity is less than 0.2.

= SSBN07 classification =

An alternative classification, introduced by B. Gladman, B. Marsden and C. van Laerhoven in 2007, uses a 10-million-year orbit integration instead of the Tisserand's parameter. Classical objects are defined as not resonant and not being currently scattered by Neptune.

{{cite book |last1=Gladman |first1=B. J. |last2=Marsden |first2=B. |last3=van Laerhoven |first3=C. |year=2008 |chapter=Nomenclature in the Outer Solar System |title=The Solar System Beyond Neptune |chapter-url=http://www.lpi.usra.edu/books/ssbn2008/7002.pdf |archive-url=https://web.archive.org/web/20121102205338/http://www.lpi.usra.edu/books/ssbn2008/7002.pdf |archive-date=2012-11-02 |url-status=live |editor-last=Barucci |editor-first=M. A. |publisher=University of Arizona Press |location=Tucson |isbn=978-0-8165-2755-7 |display-editors=etal}}

Formally, this definition includes as classical all objects with their current orbits that

are non-resonant (see the definition of the method)
have a semi-major axis greater than that of Neptune (30.1 AU; i.e. excluding centaurs) but less than 2000 AU (to exclude inner-Oort-cloud objects)
are not being scattered by Neptune
have their eccentricity $e < 0.240$ (to exclude detached objects)

Unlike other schemes, this definition includes the objects with major semi-axis less than 39.4 AU (2:3 resonance)—termed inner classical belt, or more than 48.7 (1:2 resonance) – termed outer classical belt, and reserves the term main classical belt for the orbits between these two resonances.

Families

The first known collisional family in the classical Kuiper belt—a group of objects thought to be remnants from the breakup of a single body—is the Haumea family.

{{cite journal |last1=Brown |first1=Michael E. |last2=Barkume |first2=Kristina M. |last3=Ragozzine |first3=Darin |last4=Schaller |first4=Emily L. |year=2007 |title=A collisional family of icy objects in the Kuiper belt |journal=Nature |volume=446 |issue=7133 |pages=294–6 |bibcode=2007Natur.446..294B |doi=10.1038/nature05619 |pmid=17361177 |s2cid=4430027 |url=https://authors.library.caltech.edu/34346/2/nature05619-s1.pdf |archive-url=https://web.archive.org/web/20180723192004/https://authors.library.caltech.edu/34346/2/nature05619-s1.pdf |archive-date=2018-07-23 |url-status=live}} It includes Haumea, its moons, {{mpl|2002 TX|300}} and seven smaller bodies.{{efn|As of 2008. The four brightest objects of the family are situated on the graphs inside the circle representing Haumea.{{clarify|reason=What graphs is this note referring to?|date=July 2023}}}} The objects not only follow similar orbits but also share similar physical characteristics. Unlike many other KBO their surface contains large amounts of water ice (H₂O) and no or very little tholins.

{{cite journal |last1=Pinilla-Alonso |first1=N. |last2=Brunetto |first2=R. |last3=Licandro |first3=J. |last4=Gil-Hutton |first4=R. |last5=Roush |first5=T. L. |last6=Strazzulla |first6=G. |year=2009 |title=The surface of (136108) Haumea ({{mp|2003 EL|61}}), the largest carbon-depleted object in the trans-Neptunian belt |journal=Astronomy and Astrophysics |volume=496 |issue=2 |pages=547 |arxiv=0803.1080 |bibcode=2009A&A...496..547P |doi=10.1051/0004-6361/200809733|s2cid=15139257 }} The surface composition is inferred from their neutral (as opposed to red) colour and deep absorption at 1.5 and 2. μm in infrared spectrum.

{{cite journal |last1=Pinilla-Alonso |first1=N. |last2=Licandro |first2=J. |last3=Gil-Hutton |first3=R. |last4=Brunetto |first4=R. |year=2007 |title=The water ice rich surface of (145453) 2005 RR₄₃: a case for a carbon-depleted population of TNOs? |journal=Astronomy and Astrophysics |volume=468 |issue=1 |pages=L25–L28 |arxiv=astro-ph/0703098 |bibcode=2007A&A...468L..25P |doi=10.1051/0004-6361:20077294|s2cid=18546361 }} Several other collisional families might reside in the classical Kuiper belt.{{cite journal |last1=Chiang |first1=E.-I. |title=A Collisional Family in the Classical Kuiper Belt |journal=The Astrophysical Journal |date=July 2002 |volume=573 |issue=1 |pages=L65–L68 |arxiv=astro-ph/0205275 |doi=10.1086/342089 |bibcode=2002ApJ...573L..65C |s2cid=18671789 }}{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |title=Dynamically correlated minor bodies in the outer Solar system |journal=Monthly Notices of the Royal Astronomical Society |date=11 February 2018 |volume=474 |issue=1 |pages=838–846 |arxiv=1710.07610 |doi=10.1093/mnras/stx2765 |doi-access=free |bibcode=2018MNRAS.474..838D|s2cid=73588205 }}

Exploration

File:2014 MU69 orbit.jpg

As of January 2019, only one classical Kuiper belt object has been observed up close by spacecraft. Both Voyager spacecraft have passed through the region before the discovery of the Kuiper belt.{{cite web |url=http://pluto.jhuapl.edu/News-Center/PI-Perspectives.php?page=piPerspective_02_28_2018 |title=The PI's Perspective: Why Didn't Voyager Explore the Kuiper Belt? |date=28 February 2018 |first=Alan |last=Stern |access-date=13 March 2018}} New Horizons was the first mission to visit a classical KBO. After its successful exploration of the Pluto system in 2015, the NASA spacecraft has visited the small KBO 486958 Arrokoth at a distance of {{convert|3500|km|mi}} on 1 January 2019.{{cite web |url=http://www.planetary.org/blogs/emily-lakdawalla/2018/0124-new-horizons-prepares-for-2014mu69.html |title=New Horizons prepares for encounter with 2014 MU69 |first=Emily |last=Lakdawalla |publisher=Planetary Society |date=24 January 2018 |access-date=13 March 2018}}

List

Here is a very generic list of classical Kuiper belt objects. {{As of|2023|7}}, there are about 870 objects with {{nowrap|q > 40 AU}} and {{nowrap|Q < 48 AU}}.{{cite web |url=http://minorplanetcenter.net/db_search/show_by_properties?perihelion_distance_min=40&aphelion_distance_max=48 |title={{nowrap|q > 40 AU}} and {{nowrap|Q < 48 AU}} |website=minorplanetcenter.net |department=IAU Minor Planet Center |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=31 July 2023}}

15760 Albion
20000 Varuna
{{mpl|(307261) 2002 MS|4}}
{{mpl|(307616) 2003 QW|90}}
{{mpl|(444030) 2004 NT|33}}
{{mpl|(308193) 2005 CB|79}}
{{mpl|(119951) 2002 KX|14}}
{{mpl|(120178) 2003 OP|32}}
120347 Salacia
{{mpl|(144897) 2004 UX|10}}
{{mpl|(145452) 2005 RN|43}}
{{mpl|(145453) 2005 RR|43}}
148780 Altjira
{{mpl|(15807) 1994 GV|9}}
{{mpl|(16684) 1994 JQ|1}}
174567 Varda
{{mpl|(19255) 1994 VK|8}}
19521 Chaos
{{mpl|(202421) 2005 UQ|513}}
{{mpl|(24835) 1995 SM|55}}
{{mpl|(24978) 1998 HJ|151}}
{{mpl|(278361) 2007 JJ|43}}
{{mpl|(33001) 1997 CU|29}}
486958 Arrokoth
50000 Quaoar
{{mpl|(52747) 1998 HM|151}}
53311 Deucalion
{{mpl|(55565) 2002 AW|197}}
{{mpl|(55636) 2002 TX|300}}
{{mpl|(55637) 2002 UX|25}}
58534 Logos
66652 Borasisi
{{mpl|(69987) 1998 WA|25}}
79360 Sila–Nunam
{{mpl|(79983) 1999 DF|9}}
{{mpl|(85627) 1998 HP|151}}
{{mpl|(85633) 1998 KR|65}}
{{mpl|(86047) 1999 OY|3}}
88611 Teharonhiawako
{{mpl|(90568) 2004 GV|9}}

Footnotes

References

External links

{{cite web |first=David |last=Jewitt |author-link=David Jewitt |url=http://www2.ess.ucla.edu/~jewitt/kb.html |title=Kuiper belt site |publisher=UCLA}}
{{cite web |url=http://www.boulder.swri.edu/ekonews/ |title=The Kuiper Belt Electronic Newsletter}}
{{citation |department=IAU Minor Planet Center |publisher=Harvard-Smithsonian Center for Astrophysics |url=http://www.minorplanetcenter.org/iau/lists/TNOs.html |website=minorplanetcenter.org |url-status=dead |archive-url=https://web.archive.org/web/20100827234817/http://www.minorplanetcenter.org/iau/lists/TNOs.html |archive-date=2010-08-27 |df=dmy-all |title=List of Trans-Neptunian objects}}
{{cite web |title=TNO pages |url=http://www.johnstonsarchive.net/astro/tnos.html |website=johnstonarchive.net}}
{{cite web |title=Plot of the current positions of bodies in the Outer Solar System |url=http://www.minorplanetcenter.org/iau/lists/OuterPlot.html |website=minorplanetcenter.org |department=IAU Minor Planet Center |publisher=Harvard-Smithsonian Center for Astrophysics }}