2007/11/28 by Eugene Chiang, E. Chiang · 86 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Formation and evolution of the Solar System #Instability #Mechanics #Physics #Planet #Planetesimal #Protoplanetary disk #Shearing (physics) #Solar System #Stellar, planetary, and galactic studies #Thermodynamics #astro-ph
paper · pdf · doi:10.1086/527354
published in The Astrophysical Journal 675(2), 1549-1558 (IOP Publishing) · ApJ, in press. Connections made to baroclinic instability. Movies available at http://astro.berkeley.edu/~echiang/im/im.html
arxiv created 2007/11/28 · openalex publication_date 2008/03/07 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Gravitational instability of a vertically thin, dusty sheet near the midplane of a protoplanetary disk has long been proposed as a way of forming planetesimals. Before Roche densities can be achieved, however, the dust-rich layer, sandwiched from above and below by more slowly rotating dust-poor gas, threatens to overturn and mix by the Kelvin-Helmholtz instability (KHI). Whether such a threat is real has never been demonstrated: the Richardson criterion for the KHI is derived for two-dimensional Cartesian shear flow and does not account for rotational forces. Here we present three-dimensional numerical simulations of gas-dust mixtures in a shearing box, accounting for the full suite of disk-related forces: the Coriolis and centrifugal forces, and radial tidal gravity. Dust particles are assumed small enough to be perfectly entrained in gas; the two fluids share the same velocity field but obey separate continuity equations. We find that the Richardson number Ri does not alone determine stability. The critical value of Ri below which the dust layer overturns and mixes depends on the height-integrated metallicity Σ d /Σ g (surface density ratio of dust to gas). Nevertheless, for Σ d /Σ g between 1 and 5 times solar, the critical Ri maintains a nearly constant value of ~0.1. Keplerian radial shear stabilizes those modes that would otherwise disrupt the layer at large Ri . If the height-integrated metallicity is at least ~5 times greater than the solar value of 0.01, then midplane dust densities can approach Roche densities. Such a metal-rich environment might be expected to produce gas giant planets having similarly supersolar metallicities.