migr070.html

So, what happened to the mass?

Dynamical excitation: Something excited the KB feeding most of mass inward.
- There have been three suggestions:
  1. ~Earth-mass objects scattered outward by Neptune.
    (Morbidelli & Valsecchi; Petit et al.)
  2. Uranus and Neptune scattered outward by Saturn and Jupiter (Thommes et al.)
  3. Passing star (Ida et al; Kobayashi & Ida).
- Each of these removes mass by putting it on high eccentricity orbits.
  - So, feeds the material to Neptune. Neptune migrates!!!!!!
- Neptune can't clear enough stuff to build the KBOs and remain near 30AU! (Gomes et al.)
Collisional Grinding: In an excited KB collisions grind it down. (Stern & Colwell)
. But,
- Requires a strange size distribution and very weak objects.
- It is difficult to set up a system that is stable long enough.
- Collisional grinding would have driven the secular resonance through the disk feeding most of the mass to Neptune.
- Observed KBO binaries would not have survived (Petit).

So, we need a massive disk to build the KBOs, but then we cannot get rid of it.