Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.1313b&link_type=abstract
American Astronomical Society, DPS meeting #38, #13.13; Bulletin of the American Astronomical Society, Vol. 38, p.507
Astronomy and Astrophysics
Astrophysics
Scientific paper
One of the least understood stages of planet formation is how millimeter-sized dust grains coalesce into kilometer-sized planetesimals. Goldreich & Ward (1973) and Safronov (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, including the effects of the radial Keplerian shear on the instability of the vertical shear. We follow the nonlinear evolution into turbulence and the subsequent re-mixing of the dust layer. We discuss the impact on the gravitational instability scenario of planetesimal formation. J.A.B. is supported via a NSF Astronomy & Astrophysics Postdoctoral Fellowship.
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