On the Size Dependence of the Inclination Distribution of the Main Kuiper Belt

We present a new analysis of the currently available orbital elements for the known Kuiper belt objects. In the nonresonant, main Kuiper belt, we Ðnd a statistically signiÐcant relationship between an objectÏs absolute magnitude (H) and its inclination (i). Objects with H \ 6.5 (i.e., radii km for a Z170 4% albedo) have higher inclinations than those with H [ 6.5 (radii km). We have shown that this [170 relationship is not caused by any obvious observational bias. We argue that the main Kuiper belt consists of the superposition of two distinct distributions. One is dynamically hot, with inclinations as large as D35¡ and absolute magnitudes as bright as 4.5 ; the other is dynamically cold, with and i [ 5¡ H [ 6.5. The dynamically cold population is most likely dynamically primordial. We speculate on the potential causes of this relationship.