Main Kuiper belt (~43<a<48 AU) probably contains superimposed populations:
- Bimodal inclination distribution. (Brown) Cold pop width 1.8 degrees, hot width 12 degrees.
- The two populations have different absolute magnitude distributions (Levison & Stern)
- Result recently confirmed by (Trujillo & Brown; Bernstein et al.)
- The two populations have different colors
(Trujillo & Brown; Tegler & Romanishin; Doressoundiram et al).
- Implies they formed in different regions of the proto-planetary disk and then overlaid.
Hot population formed:
- closer to the Sun and scattered outward by Neptune. (Levison & Stern)
- farther from the Sun and scattered inward by a passing star. (Kobayashi et al.)