Paper: astro-ph/0509701
Date: Thu, 22 Sep 2005 21:20:00 GMT (996kb)

Title: Planetesimal growth in turbulent discs before the onset of
gravitational instability

Authors: Alexander Hubbard (U. Rochester) and Eric G. Blackman (U. Rochester)

Categories: astro-ph

Comments: Submitted to MNRAS
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Standard models for planet formation require gravitationally unstable discs.
Initially unstable gas-dust discs may form planets directly, but the high
surface density required has motivated the alternative that gravitational
instability occurs in a dust sub-layer only after grains have grown large
enough by electrostatic sticking. Although such growth up to the instability
stage is efficient for laminar discs, concern has mounted as to whether
realistic disc turbulence catastrophically increases the settling time, thereby
requiring additional processes to facilitate planet formation on the needed
time scales. To evaluate this concern, we develop a model for grain growth that
accounts for the influence of turbulence on the collisional velocity of grains
and on the scale height of the dust layer. The relative effect on these
quantities depends on the grain size. The model produces a disc-radius
dependent time scale to reach the gravitationally unstable phase of planet
formation. For a range of dust sticking and disc parameters, we find that for
viscosity parameters $\alpha < 10^{-3}$, this time scale is short enough over a
significant range in radii $R$ that turbulence does not catastrophically slow
the early phases of planet formation, even in the absence of agglomeration
enhancement agents like vortices.

\\ ( http://arXiv.org/abs/astro-ph/0509701 , 996kb)