Orchestra: Coagulation
Growth by collision and merger
- Statistical approach to inelastic collisions
- Fragmentation algorithm for collision outcomes
- Fokker-Planck approach to gravitational encounters and elastic collisions
Advantages
- Essential for 1015 or more planetesimals
- Calculate evolution of small planets accurately
- Calculate collisional cascade well
Disdvantages
- Fail when most of the mass in a few large objects
- Cannot predict final mass of planet
- Cannot model formation of gas giant planets
Approach
- Divide disk into concentric annuli
- Within each annulus, mass bins from 10-15 kg to 1027 kg
- Particles in all annuli interact
- Collision rates: particle-in-a-box with gravitational focusing
- Dynamics: dynamical fraction, gas drag, P-R drag, viscous stirring
Code is extensively tested