Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk: Ideal Unstratified Disks

The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations due to magnetorotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model has turbulent accretion characterized by a Shakura-Sunyaev viscosity parameter of α ∼ 10, with root-mean-square density perturbations of ∼10%. We present detailed characterizations of the statistical evolution of particle orbital properties in our simulations. Contrary to recent claims, we find that planetesimals should be safe from turbulence-induced collisional destruction, except perhaps for kilometer-sized objects situated in the outer regions (&30 AU) of young protoplanetary disks. We confirm earlier results based on local models indicating that type-I migration probably dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magnetorotationally unstable disks remains a major open issue, with important consequences for planet formation scenarios.