EAS Publications Series
Volume 41, 2010Physics and Astrophysics of Planetary Systems
|Page(s)||187 - 207|
|Published online||08 January 2010|
T. Montmerle, D. Ehrenreich and A.-M. Lagrange (eds)
EAS Publications Series, 41 (2010) 187-207
From Grains to Planetesimals
C.I.T.A., University of Toronto, 60 St. George St., Toronto, ON M5S 3H8, Canada
This pedagogical review covers an unsolved problem in the theory of protoplanetary disks: the growth of dust grains into planetesimals, solids at least a kilometer in size. I summarize timescale constraints imposed on planetesimal formation by circumstellar disk observations, analysis of meteorites, and aerodynamic radial migration. The infall of ≲ meter-sized solids in a hundred years is the most stringent constraint. I review proposed mechanisms for planetesimal formation. Collisional coagulation models are informed by laboratory studies of microgravity collisions. The gravitational collapse (or Safronov-Goldreich-Ward) hypothesis involves detailed study of the interaction between solid particles and turbulent gas. I cover the basics of aerodynamic drag in protoplanetary disks, including radial drift and vertical sedimentation. I describe various mechanisms for particle concentration in gas disks – including turbulent pressure maxima, drag instabilities and long-lived anticylonic vortices. I derive a general result for the minimum size for a vortex to trap particles in a sub-Keplerian disk. Recent numerical simulations demonstrate that particle clumping in turbulent protoplanetary disks can trigger gravitational collapse. I discuss several outstanding issues in the field.
© EAS, EDP Sciences, 2010
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