A cubewano is a Kuiper belt object, orbiting beyond Pluto and not controlled by resonances with Neptune. Cubewanos, also called Classical Kuiper Belt objects, have semi-major axes in 40-50 AU range and, unlike Pluto, do not cross Neptune’s orbit. The odd name is derived from the first trans-Neptunian object found, . Later objects were called "QB1-o's", or cubewanos.

Objects identified as cubewanos include:

• the largest known cubewano and one of the largest trans-Neptunian objects
• , notable for its two moons and rapid rotation (3.9h)
• (50000) Quaoar
• (20000) Varuna
• (19521) Chaos
• (53311) Deucalion

Orbits

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Most classical Kuiper objects are found between the 2:3 orbital resonance with Neptune (populated by plutinos) and the 1:2 resonance. The diagram illustrates larger cubewanos with semi-major axis on X axis. The eccentricity of the orbits is represented by red segments (extending from perihelion to aphelion) with inclination represented on Y axis.

The largest plutinos (Pluto, 90482 Orcus and 28978 Ixion) are also plotted for comparison (in grey). 50000 Quaoar, for example, has a typical, near circular (short red segment), close to the ecliptic orbit. Plutinos on the other hand, have more eccentric orbits bringing some of them closer to the Sun than Neptune (marked as 1:1 resonance).

The majority of objects, so called cold population, have low inclination, near circular orbits. (the brightest: , and are shown on the diagram). A smaller population, named hot, is characterised by highly inclined, more eccentric orbitsD.Jewitt,A.Delsanti The Solar System Beyond The Planets,to appear in the book Solar System Update, Springer-Praxis Ed., Horwood, Blondel and Mason, 2006. Preprint version (pdf).

Distribution

The distribution of all known cubewanos (532 as of February, 2006) is plotted on the second diagram. The small inserts on the right show histograms for orbit inclinations i (5° interval) and eccentricity e (interval 0.05).¹ The vast majority of objects (more than ²/₃) have inclination < 5° and eccentricity <0.1. The distribution of semi-major axis a, also shown, illustrates the 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 inserts on the left side of the diagram compare the populations of cubewanos and plutinos Minor Planet Circular 2005-X77 Distant Minor planets was used for plutinos' orbits classification. The updated data can be found in MPC 2006-D28. using eccentricity versus inclination plots. Each small square represents a given range for both the eccentricity e and the inclination i ². The relative population of objects within this range is represented with ‘cartographic’ colours (from small numbers plotted as green valleys to brown peaks³.

The two populations are quite different: more than 30% of all cubewanos are on low inclination, near circular orbits (the low bottom corner ‘peak’). The parameters of 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.

¹Distribution of plutinos is plotted but excluded from cubewanos’ histograms. ²As near-circular orbits occupy the first column (e<0.05) and the orbits with the lowest inclination (i<5 degrees) occupy the lowest row, the square in the bottom left corner represents the number of near circular, very lowly inclined orbits. ³A grey square represents a single object (an outlier) in this range.

Orbit plots

The graph on the left represents polar and ecliptic views of the (aligned) orbits of the classical objects (in blue) together with the plutinos (in red)¹.

The solid blue ring, resulting from hundreds of overlapping orbits of the classical objects, fully deserves the name of the main (classical or cubewanos) belt. Unlike the classical objects with the orbits entirely outside, the plutinos approach, or even cross, the orbit of Neptune (in yellow).

On the ecliptic view, the yellow arc represents Neptune’s orbit (at ~30AU). The perihelion, typically inside Neptune’s orbit for the plutinos, and always safely outside for the cubewanos, is the distinctive attribute between the two families. Hot cubewanos can also be easily distinguished by their inclination, the plutinos typically keeping orbits below 20°.

^{1For roughly a half of known TNO the orbits are not yet known with the precision sufficient for the classification (a particularly delicate task for resonant objects).}

External links

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• David Jewitt's Kuiper Belt site @ University of Hawaii
• The Kuiper Belt Electronic Newsletter
• Minor Planet Center List of Trans-Neptunian objects
• TNO pages at johnstonarchive
• Plot of the current positions of bodies in the Outer Solar System

References

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Trans-Neptunian objects

Cubewano | Kubewano | Cubewano | Cubewano | Cubewano | Cubewano | キュビワノ族 | Cubewano | Kubewano | Cubewano | 類QB1天體 | Cubewano