Dead zones as safe-havens for planetesimals: influence of disc mass and external magnetic field

Abstract

(Abridged) Planetesimals embedded in a protoplanetary disc are stirred by gravitational torques exerted by density fluctuations in the surrounding turbulence. In particular, planetesimals in a disc supporting fully developed magneto-rotational turbulence are readily excited to velocity dispersions above the threshold for catastrophic disruption, halting planet formation. We aim to examine the stirring of planetesimals lying instead in a magnetically-decoupled midplane dead zone, stirred only by spiral density waves propagating out of the disc's magnetically-coupled turbulent surface layers. We extend previous studies to include a wider range of disc models, and explore the effects of varying the disc column density and external magnetic field strength. [...] The strength of the stirring is found to be independent of the gas surface density, which is contrary to the increase with disc mass expected from a simple linear wave picture. The discrepancy arises from the shearing out of density waves as they propagate into the dead zone, resulting in density structures near the midplane that exert weaker stochastic torques on average. We provide a simple analytic fit to our numerically obtained torque amplitudes that accounts for this effect. The stirring on the other hand depends sensitively on the net vertical magnetic flux, up to a saturation level above which magnetic forces dominate in the turbulent layers. For the majority of our models, the equilibrium planetesimal velocity dispersions lie between the thresholds for disrupting strong and weak aggregates, suggesting that collision outcomes will depend on material properties. However, discs with relatively weak magnetic fields yield reduced stirring, and their dead zones provide safe-havens even for the weakest planetesimals against collisional destruction.

20 pages, 18 figures, 3 tables, to be published in MNRAS

References in corpus (12)

• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Towards planetesimals: dense chondrule clumps in the protoplanetary nebula
• The Compositional Structure of the Asteroid Belt
• Magnetic fields in protoplanetary disks
• Dead Zone Accretion Flows in Protostellar Disks
• Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence
• Accretion and destruction of planetesimals in turbulent disks
• Turbulent Torques on Protoplanets in a Dead Zone
• Rapid Formation of Icy Super-Earths and the Cores of Gas Giant Planets
• Turbulent transport and its effect on the dead zone in protoplanetary discs
• On the dynamics of planetesimals embedded in turbulent protoplanetary discs with dead zones
• Shearingbox-implementation for the central-upwind, constraint-transport MHD-code NIRVANA

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