From Grains to Planetesimals: Les Houches Lecture

Abstract

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.

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

References in corpus (12)

• Rapid planetesimal formation in turbulent circumstellar discs
• Particle Stirring in Turbulent Gas Disks: Including Orbital Oscillations
• Protoplanetary Disk Turbulence Driven by the Streaming Instability: Non-Linear Saturation and Particle Concentration
• A Submillimeter View of Circumstellar Dust Disks in $\rho$ Ophiuchus
• Protoplanetary Disk Turbulence Driven by the Streaming Instability: Linear Evolution and Numerical Methods
• Dust sedimentation and self-sustained Kelvin-Helmholtz turbulence in protoplanetary disk mid-planes. I. Radially symmetric simulations
• Convective cooling and fragmentation of gravitationally unstable disks
• Evolution of Mid-IR Excess Around Sun-like Stars: Constraints on Models of Terrestrial Planet Formation
• Turbulent Torques on Protoplanets in a Dead Zone
• Midplane sedimentation of large solid bodies in turbulent protoplanetary discs
• Vertical Shearing Instabilities in Radially Shearing Disks: The Dustiest Layers of the Protoplanetary Nebula
• Numerical simulations of type III planetary migration: II. Inward migration of massive planets

Cited by in corpus (31)

• Rapid growth of gas-giant cores by pebble accretion
• Forming Planetesimals in Solar and Extrasolar Nebulae
• Concentrating small particles in protoplanetary disks through the streaming instability
• The Exoplanet Census: A General Method, Applied to Kepler
• On the Formation of Planetesimals via Secular Gravitational Instabilities with Turbulent Stirring
• Particle Concentration At Planet Induced Gap Edges and Vortices: I. Inviscid 3-D Hydro Disks
• Thresholds for Particle Clumping by the Streaming Instability
• High-resolution simulations of planetesimal formation in turbulent protoplanetary discs
• Grain Growth in the Circumstellar Disks of the Young Stars CY Tau and DoAr 25
• A New Hybrid N-Body-Coagulation Code for the Formation of Gas Giant Planets
• Planetesimal Accretion in Binary Systems: Could Planets Form Around Alpha Centauri B ?
• Migration of planets embedded in a circumstellar disk
• Circumbinary Chaos: Using Pluto's Newest Moon to Constrain the Masses of Nix & Hydra
• How do giant planetary cores shape the dust disk? HL Tau system
• Application of gas dynamical friction for planetesimals: I. Evolution of single planetesimals
• Relative velocities of inertial particles in turbulent aerosols
• From Disks to Planets
• Streaming Instability of Multiple Particle Species in Protoplanetary Disks
• Vortices as nurseries for planetesimal formation in protoplanetary discs
• From Pebbles and Planetesimals to Planets and Dust: the Protoplanetary Disk--Debris Disk Connection
• Dust clearing by radial drift in evolving protoplanetary discs
• Earth and Terrestrial Planet Formation
• On the Origin of Dust Structures in Protoplanetary Disks: Constraints from the Rossby Wave Instability
• The angular momentum of two collided rarefied preplanetesimals and the formation of binaries
• The Role of Non-ionizing Radiation Pressure in Star Formation: The Stability of Cores and Filaments
• Erosion of planetesimals by gas flow
• Gas Absorption in the KH 15D System: Further Evidence for Dust Settling in the Circumbinary Disk
• Observation of aerodynamic instability in the flow of a particle stream in a dilute gas
• M dwarf stars in the light of (future) exoplanet searches
• Zero Age Planetary Orbit of Gas Giant Planets Revisited: Reinforcement of the Link with Stellar Metallicity
• Models and Observational Predictions of Dust Traps in Protoplanetary Discs