The PSI Planetbuilding Code: Multizone, Multiuse

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

• S. J. Weidenschilling
• PSI Retreat
• August 20, 2007

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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

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• 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 dont overlap
• Explicit transport of mass between zones due to
  collisions, gas drag, tidal interactions with
  nebula, shepherding by massive bodies, etc.

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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

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• 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)

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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

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Collisional evolution of the asteroid belt Dust
production
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Collisional evolution of planetesimal swarm
during migration of outer planets
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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 gt 10 My
• Extension to small particle sizes, with radiation
  pressure and Poynting-Robertson drag
• Parallel version with symplectic N-body integrator