So, what happened to the mass?
- Dynamical excitation: Something excited the KB feeding most of mass inward.
- Could also explain some aspects of the KB orbital element distribution.
- There have been many suggestions. For example:
- ~Earth-mass objects scattered outward by Neptune. (Morbidelli & Valsecchi; Petit et al.)
- Passing star (Ida et al; Kobayashi & Ida).
- Unseen planet at large heliocentric distance. (Brunini & Melita)
- Each remove mass by putting it on high eccentricity orbits Neptune migrates!!!!!!
- Neptune can't remove enough stuff to clear the KBOs and remain near 30AU! (Gomes et al.)
- Collisional Grinding: In an excited KB collisions grind it down. (Stern & Colwell)
- Requires a strange size distribution — steep down to 10-100m — and
very weak objects — Q*<10% of Benz & Asphaug's value. (Kenyon & Bromley)
- If like this, the scattered disk would not have enough comets.(Charnoz & Morbidelli)
- KB might not grind down before Neptune migrates through. (Gomes et al.)
- Observed KBO binaries would not have survived (Petit & Mousis).
- Collisional grinding would have driven the ν8 secular resonance through the disk feeding most of the mass to Neptune.
- To remove this much mass in the required time implies the optical depth of disk >>100!
- With no light, how do you get rid of the dust?
- Much more massive than β-Pic.
So, we need a massive disk to build the KBOs, but then we cannot get rid of it.