Editing Classical Kuiper belt object (section)

== {{vanchor|Orbits 'hot' and 'cold' populations}} ==
[[File:TheKuiperBelt 55AU Classical.svg|thumb|300px|[[Semimajor axis]] and [[orbital inclination|inclination]] of cubewanos (blue) compared to [[Resonant trans-Neptunian object|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 [[plutino]]s) 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 (<&thinsp;5[[Degree (angle)|°]]) and near-circular orbits, lying between 42 and 47&nbsp;AU. A smaller population (the ''hot population'') is characterised by highly inclined, more eccentric orbits.<ref name="JewittDelsanti2006">{{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 (publisher)|Springer]]-[[Praxis Publishing|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}})</ref> 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.<ref name="Levison2003">{{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 (journal)|Nature]] |volume=426 |issue=6965 |pages=419–421 |doi=10.1038/nature02120 |pmid=14647375 |bibcode=2003Natur.426..419L|s2cid=4395099 }}</ref>

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'').<ref name="DES_Elliot2006">
{{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}})</ref>

=== Distribution ===
The vast majority of KBOs (more than two-thirds) have inclinations of less than 5° and eccentricities of less than 0.1&nbsp;. 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#Scattered objects versus classical objects|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.<ref>
{{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}}</ref>

{{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 trans-Neptunian object|resonant TNOs]] (red), [[Scattered disk object|SDO]]s (grey) and [[sednoid]]s (yellow). ''Right:'' Comparison of the aligned orbits (polar and ecliptic view) of cubewanos, plutinos, and Neptune (yellow).
}}
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