Нептунмен резонанссыз Куйпер белдегі объектілер

Kuiper belt object, not controlled by an orbital resonance with Neptune

A classical Kuiper belt object, also called a cubewano (,/k//juː//b//iː/'/w//ʌ//n//oʊ/ "QB1 o"), 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) 1992 QB1. Similar objects found later were often called "QB1 o's", 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 but was later found to be in a resonant orbit.

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. 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. 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).

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. When the orbital eccentricities of cubewanos and plutinos are compared, it can be seen that the 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 below 20°. (No clear explanation currently exists for the inclinations of 'hot' cubewanos.)

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. 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. 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.

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. 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 on 1 January 2019.