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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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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.