The PSI Planet-building Code: Multi-zone, Multi-use

S. J. Weidenschilling

PSI RetreatAugust 20, 2007

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

• 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.

Discrete Bodies

• Bodies larger than threshold mass (~1024 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

• 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)

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

Collisional evolution of the asteroid belt: Dust production

Collisional evolution of planetesimal swarm during migration of outer planets

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