Planetesimal Formation by Gravitational Instability

By A. Youdin, F. Shu. 2002

413 citations recorded by the source corpus.

We investigate the formation of planetesimals via the gravitational instability of solids that have settled to the midplane of a circumstellar disk. Vertical shear between the gas and a subdisk of solids induces turbulent mixing that inhibits gravitational instability. Working in the limit of small, well-coupled particles, we find that the mixing becomes ineffective when the surface density ratio of solids to gas exceeds a critical value. Solids in excess of this precipitation limit can undergo midplane gravitational instability and form planetesimals. However, this saturation effect typically requires increasing the local ratio of solid to gaseous surface density by factors of 2-10 times cosmic abundances, depending on the exact properties of the gas disk. We discuss existing astrophysical mechanisms for augmenting the ratio of solids to gas in protoplanetary disks by such factors and investigate a particular process that depends on the radial variations of orbital drift speeds induced by gas drag. This mechanism can concentrate millimeter-sized chondrules to the supercritical surface density in ≤ few × 106 yr, a suggestive timescale for the disappearance of dusty disks around T Tauri stars. We discuss the relevance of our results to some outstanding puzzles in planet formation theory—the size of the observed solar system and the rapid type I migration of Earth-mass bodies.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ce255a90b5dc9ec8e56292d72e110d7755e7d15c

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Citations in the corpus

Multiple Disk Gaps and Rings Generated by a Single Super-Earth (2017, background): “Once dust is concentrated into rings, coagulation can be facilitated (e.g., Youdin & Shu 2002; Johansen et al. 2007; Pinilla et al. 2016), and instabilities such as the streaming instability (Youdin & Goodman 2005; Chiang & Youdin 2010) can be triggered.”
Planetary accretion in the inner Solar System (2004, background): “The local solid to gas ratio can also increase over time as small solids migrate inwards [42], or as gas escapes from the Solar System due to photoevaporation by ultraviolet light from the Sun.”
PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR (2008, background): “Since larger particles are decoupled to the flow and may remain in the disk, photoevaporation can decrease the ratio of gas surface density to the dust surface density in disks (see Throop & Bally (2005) and Youdin & Shu (2002) for a discussion of the possible consequences).”
Forming Planetesimals in Solar and Extrasolar Nebulae (2009, background): “Enriching the disk in metals, say by photoevaporation of gas (Throop & Bally 2005, Gorti & Hollenbach 2009, Ercolano et al. 2009) or by radial drifts of particles (Youdin & Shu 2002, hereafter YS), can stop vertical shear turbulence from forestalling GI (Sekiya 1998, YS, Chiang 2008).”
Gravoturbulent Formation of Planetesimals (2005, background): “The subsequent Kelvin-Helmholtz turbulence puffs up the dust layer so that the densities needed for a gravitational instability are usually not achieved, unless a dust-to-gas ratio many times higher than the solar composition is adopted (Youdin & Shu 2002).”
Building the terrestrial planets: Constrained accretion in the inner Solar System (2009, background): “This barrier may be crossed by rapid accretion (Weidenschilling & Cuzzi 1993; Benz 2000) or by local gravitational instability (Goldreich & Ward 1973; Youdin & Shu 2002), which can be triggered by turbulent concentration (Johansen et al. 2007; Cuzzi et al. 2008).”
Planet formation bursts at the borders of the dead zone in 2D numerical simulations of circumstellar disks (2009, background): “A distinct alternative is gravitational instability of the layer of solids (Safronov 1969, Lyttleton 1972; Goldreich & Ward 1973; Youdin & Shu 2002).”
Grain Retention and Formation of Planetesimals near the Snow Line in MRI-driven Turbulent Protoplanetary Disks (2007, background): “…AU can be retained and then converted into planetesimals either through sedimentation followed by gravitational instability (Goldreich & Ward 1973; Youdin & Shu 2002; Garaud & Lin 2004) or through cohesive collisions (Supulver & Lin 2000) after the photoevaporation of disk gas increases Z above…”
MAKE SUPER-EARTHS, NOT JUPITERS: ACCRETING NEBULAR GAS ONTO SOLID CORES AT 0.1 AU AND BEYOND (2014, background): “This decreasing metallicity profile is readily explained by solid particles drifting inward by aerody- namic drag and possibly piling up (Youdin & Shu 2002; Youdin & Chiang 2004; Birnstiel et al. 2012; Hansen & Murray 2013; Chatterjee & Tan 2014; Schlichting 2014).”
Forming the cores of giant planets from the radial pebble flux in protoplanetary discs (2014, background): “The outer parts of the protoplanetary discs act as reservoir of solid particles (Youdin & Shu 2002; Garaud 2007).”
Dust Growth and Settling in Protoplanetary Disks and Disk Spectral Energy Distributions. I. Laminar Disks (2005, background): “In the dust layer, a large number of planetesimals are thought to form as the first step of planetary formation (e.g., Goldreich & Ward 1973; Weidenschilling 1997; Youdin & Shu 2002).”
How to form planetesimals from mm-sized chondrules and chondrule aggregates (2015, background): “A number of global processes increase the local solid concentration, including radial drift of particles from the outer disk into the inner disk (Youdin & Shu 2002), large scale pressure bumps or vortices (Johansen et al. 2009a), and lastly, there is a region near the ice line where ice-dust…”
Protoplanetary Disks and Their Evolution (2011, background): “…in long-lived vortices (e.g., Heng & Kenyon 2010), or via the gravitational instability of millimeter-sized chondrules in a gas deficient subdisk (e.g., Youdin & Shu 2002), overcoming this barrier remains one of the biggest challenges for planet formation theories (Chiang & Youdin 2010).”
Particle Pileups and Planetesimal Formation (2003, background): “The formation of planetesimals by gravitational instability within dense particle layers in circumstellar disks is an appealing alternative to collisional sticking of dust aggregates (Youdin & Shu 2002, hereafter YS02, and references therein).”
Correlated accretion ages and ε54Cr of meteorite parent bodies and the evolution of the solar nebula (2014, background): “Theoretically, there are two scenarios of planetesimal formation, grain by grain accretion (Adachi et al. 1976; Brauer et al. 2008) and formation by gravitational instability in a dense midplane (Youdin and Shu 2002).”
PARTICLE CLUMPING AND PLANETESIMAL FORMATION DEPEND STRONGLY ON METALLICITY (2009, background): “Assume that the sub-layer thicknessis set by vertical shear turbulence to beHp ∼∆v/(2Ω) as appropriate for small particles (Sekiya 1998; Youdin & Shu 2002).”