Everything about Classical Kuiper Belt Object totally explained
In astronomy a
cubewano ((stress?)) is a
Kuiper belt object that
orbits beyond
Neptune and isn't controlled by an
orbital resonance with the giant planet. Cubewanos have
semi-major axes in the 40-50
AU range and, unlike
Pluto, don't cross Neptune’s orbit. They are also called
classical Kuiper Belt objects.
The odd name derives from the first
trans-Neptunian object (TNO) found (besides Pluto and
Charon), . Later objects were called "QB1-o's", or cubewanos.
Objects identified as cubewanos include:
-
- the largest known cubewano and one of the largest TNOs
- , notable for its elongated shape, two moons and rapid rotation (3.9h)
- (50000) Quaoar and (20000) Varuna, each considered the largest TNO at the time of discovery
- ,,
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 objects (the so-called 'cold population'), have low inclinations and near circular orbits. A smaller population (the 'hot population') is characterised by highly inclined, more eccentric orbits.
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).
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.
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 orbits. When orbital inclinations are compared, 'hot' cubewanos can be easily distinguished by their higher inclinations, as the plutinos typically keep orbits below 20°.
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). Furthermore, there's 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. 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's between 39.4 and 47.8 AU (with exclusion of these resonances and the minor ones in-between).
Families
The first
collisional family, for example a group of objects thought to be remnants of a single body has been identified. It includes, its moons, and four smaller bodies
†. The objects not only follow similar orbits but also share similar physical characteristics. Unlike many other KBO their surface contains large amounts of ice (H
2O) and no or very little
tholins. 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.
†The four brightest objects of the family are situated on the graphs inside the circle representing .Further Information
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