The Time-Scale Problem
- It has been difficult to grow the cores of Jupiter and Saturn before the gas goes away.
- Disks last 3-5 Myr. (Earth took between 50 and 100Myr to form!)
- Proposed Solutions have been:
- Embryo Atmospheres: (Inaba & Ikoma)
- Captured extended atmospheres can significantly increase crossection.
- Shear-Dominated Accretion:
- Growth can be fast if scale height of particle disk is smaller then Hill sphere (RH).
- Shear-dominated regime.
- Collisional Damping: (Goldriech et al.)
- As embryos excite planetesimals collisions will fragmentation.
- planetesimals will adjust size until mean free path is small
damping.
- This helps because there is no significant radial migration.
- unlike with aerodynamic drag.
- Evaporation/Condensation Near Snow-Line: (Stevenson & Lunine)
- As planetesimals migrate inward due to drag the evaporate at snow-line.
- Some water diffuses outward and recondenses larger solid surface density.
But none of this has been tested in a full N-body simulation.
