Cubewanos, or Classical Kuiper belt objects, are low-eccentricity (below 0.15) Kuiper belt objects (KBO) that orbit beyond Neptune and are 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.
There are 301 cubewanos identified, as of 2011.
Naming
The name "cubewano" derives from the first trans-Neptunian object (TNO) found after Pluto and Charon, (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.
Orbit
Most cubewanos are found between the plutinos (2:3 orbital resonance with Neptune) and the twotinos (1:2 orbital resonance with 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).
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).
Physical Characteristics
The difference in colour between the red cold population 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° between the cold and hot populations while confirming 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.
No comments:
Post a Comment