Cold and Hot Populations: Physical Characteristics
In addition to the distinct orbital characteristics the two populations display different 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° (instead of 5°) 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.
Read more about this topic: Classical Kuiper Belt Object
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