1. The PSI Planet-building Code: Multi-zone, Multi-use S. J. Weidenschilling PSI Retreat August 20, 2007

2. Hybrid Collisional Code Neither particle-in-a-box nor N-body Designed to treat radially extended swarm of bodies orbiting a star Large dynamic size range, from dust grains to giant planets Both serial and parallel versions

3. Collisions and stirring occur when orbits overlap, even for different zones (not a series of separate particle-in-box simulations) Mutual gravitational stirring and dynamical friction (energy exchange) for bodies in crossing orbits Long-range perturbations by large bodies, even if orbits don’t overlap Explicit transport of mass between zones due to collisions, gas drag, tidal interactions with nebula, “shepherding” by massive bodies, etc.

4. Discrete Bodies Bodies larger than threshold mass (~10 24 g) are treated as discrete Allows late-stage simulations after large bodies have formed Individual values of M, a, e, i evolve with time Interact with continuum by viscous stirring, dynamical friction

5. Gravitational scattering of discrete bodies treated as stochastic events, allows impulsive changes in orbital elements Angular orbital elements assumed evenly distributed, scattering treated as 2-body interactions New version of serial code includes a symplectic N-body integrator Discrete bodies can be designated with specified masses and orbits (i.e., planets)

6. Example Calculation: Accretion in Inner Solar System Planetesimal swarm 0.5 - 4 AU Swarm mass ~ 7 Earth masses Initial planetesimal diameter 1 km Fragments retained to d = 1/8 km Model time to 5 MY

29. Collisional evolution of the asteroid belt: Dust production

30. Collisional evolution of planetesimal swarm during migration of outer planets

31. Under Development Secular perturbations on planetesimals and embryos due to giant planets or stellar companions Modeling circumstellar debris disks, including dust production over stellar lifetimes ~ > 10 My Extension to small particle sizes, with radiation pressure and Poynting-Robertson drag Parallel version with symplectic N-body integrator