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How do hot classical Kuiper belt objects differ from cold classical Kuiper belt objects?
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Kuiper belt
An artist's rendition of a binary object in the Kuiper belt. The two objects depicted orbit each other at the edge of the solar system.
Hot and cold classical Kuiper belt objects (KBOs) are distinguished primarily by their orbital characteristics.1
- Hot Classicals: These objects exhibit a wide distribution of orbital inclinations, averaging about 16°. Their perihelion distances—the points in their orbits closest to the Sun—typically range between 35 and 40 AU. This population is estimated to include approximately 120,000 objects larger than 100 km in diameter.1
- Cold Classicals: In contrast, these objects are characterized by a narrow distribution of orbital inclinations, averaging about 2.6°. Their mean orbital distances are restricted to a range of 42.5–47.2 AU, with perihelion distances smoothly distributed between 38 and 47.2 AU. This population consists of approximately 75,000 objects larger than 100 km in diameter.1
Within the cold classical population, there is a distinct subpopulation known as the "kernel," which features even more specific orbital parameters, including semimajor axes between 43.8 and 44.4 AU and low orbital eccentricities.1