AAS 207th Meeting, 8-12 January 2006
Session 196 Star Formation Grab Bag II
Oral, Thursday, 10:00-11:30am, January 12, 2006, Wilson A/B

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[196.02] Three-dimensional simulations of Kelvin-Helmholtz instability in the dusty midplane of a protoplanetary disk

J.A. Barranco (Harvard-Smithsonian CfA)

One of the least understood stages of planet formation is how millimeter-sized dust grains coalesce into kilometer-sized planetesimals. Goldreich & Ward (1973) and Safranov (1960) proposed that dust grains would settle into a thin sub-layer in the midplane of a protoplanetary disk; and that such a layer would be gravitationally unstable and clump up directly into planetesimals. Weidenschilling & Cuzzi (1993) argued that a dust sub-layer would set up a vertical shear profile that would be unstable to Kelvin-Helmholtz-like instabilities. Pure gas orbits the protostar at a rate slightly slower than the true Keplerian rate because the weak outward radial pressure gradient partially cancels the radial component of gravity. A layer of particles, on the other hand, orbits exactly at the Keplerian rate. In the case of a dusty midplane, the dust particles would drag the gas forward so that the midplane would rotate faster than the dust-depleted regions above and below the midplane. We have computed fully three-dimensional hydrodynamic simulations of this shear instability, and its nonlinear evolution into turbulence and the re-mixing of the dust layer. We discuss the impact of this instability on the gravitational instability scenario of planetesimal formation. J.A.B. is supported via a NSF Astronomy & Astrophysics Postdoctoral Fellowship.

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