2008/07/11 by Andrew N. Youdin, Andrew Youdin · 61 citations
Physics and Astronomy · #Aerodynamic drag #Astro and Planetary Science #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Drag #Formation and evolution of the Solar System #Gravitational collapse #Mechanics #Physics #Planet #Planetesimal #Protoplanet #Protoplanetary disk #Stellar, planetary, and galactic studies #Turbulence #Vortex #astro-ph
paper · pdf · doi:10.1051/eas/1041016
published in EAS Publications Series 41, 187-207 (EDP Sciences) · 20 pages, 3 figures, to appear in the proceedings of the Les Houches Winter School "Physics and Astrophysics of Planetary Systems" (EDP Sciences: EAS Publications Series). Version 2 is the same paper, simply adds above publisher info
arxiv created 2008/07/11 · openalex publication_date 2010/01/01 · arxiv updated 2015/05/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
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.