Dynamics of Protoplanetary Disks

Protoplanetary disks are quasi-steady structures whose evolution and dispersal determine the environment for planet formation. I review the theory of protoplanetary disk evolution and its connection to observations. Substantial progress has been made in elucidating the physics of potential angular momentum transport processes - including self-gravity, magnetorotational instability, baroclinic instabilities, and magnetic braking - and in developing testable models for disk dispersal via photoevaporation. The relative importance of these processes depends upon the initial mass, size and magnetization of the disk, and subsequently on its opacity, ionization state, and external irradiation. Disk dynamics is therefore coupled to star formation, pre-main-sequence stellar evolution, and dust coagulation during the early stages of planet formation, and may vary dramatically from star to star. The importance of validating theoretical models is emphasized, with the key observations being those that probe disk structure on the scales, between 1 AU and 10 AU, where theory is most uncertain.Comment: Annual Review of Astronomy and Astrophysics (2011). Final edited version at http://www.annualreviews.org/doi/abs/10.1146/annurev-astro-081710-102521 .High resolution versions of illustrations at http://jila.colorado.edu/~pja/araa.htm

On the formation time scale and core masses of gas giant planets

Numerical simulations show that the migration of growing planetary cores may be dominated by turbulent fluctuations in the protoplanetary disk, rather than by any mean property of the flow. We quantify the impact of this stochastic core migration on the formation time scale and core mass of giant planets at the onset of runaway gas accretion. For standard Solar Nebula conditions, the formation of Jupiter can be accelerated by almost an order of magnitude if the growing core executes a random walk with an amplitude of a few tenths of an au. A modestly reduced surface density of planetesimals allows Jupiter to form within 10 Myr, with an initial core mass below 10 Earth masses, in better agreement with observational constraints. For extrasolar planetary systems, the results suggest that core accretion could form massive planets in disks with lower metallicities, and shorter lifetimes, than the Solar Nebula.Comment: ApJL, in pres