Rapid planetesimal formation in turbulent circumstellar disks

By Anders Johansen, Jeffrey S. Oishi, M. Low, H. Klahr, Th. Henning, A. Youdin. Nature, 2007

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During the initial stages of planet formation in circumstellar gas disks, dust grains collide and build up larger and larger bodies. How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem: boulders are expected to stick together poorly, and to spiral into the protostar in a few hundred orbits owing to a ‘headwind’ from the slower rotating gas. Gravitational collapse of the solid component has been suggested to overcome this barrier. But even low levels of turbulence will inhibit sedimentation of solids to a sufficiently dense midplane layer, and turbulence must be present to explain observed gas accretion in protostellar disks. Here we report that boulders can undergo efficient gravitational collapse in locally overdense regions in the midplane of the disk. The boulders concentrate initially in transient high pressure regions in the turbulent gas, and these concentrations are augmented a further order of magnitude by a streaming instability driven by the relative flow of gas and solids. We find that gravitationally bound clusters form with masses comparable to dwarf planets and containing a distribution of boulder sizes. Gravitational collapse happens much faster than radial drift, offering a possible path to planetesimal formation in accreting circumstellar disks.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/983a537064ec6c967b592c480521f46d0a6c5eb6

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Citations in the corpus

Probing dust grain evolution in IM Lupi's circumstellar disc. Multi-wavelength observations and mo (2008, background): “…formation of a dust sub-disc close to the equatorial plane (e.g., Safronov & Zvjagina 1969; Dubrulle et al. 1995) that may become unstable and produce planetesimals when the density of the dust layer exceeds the gas one (e.g., Goldreich & Ward 1973; Schräpler & Henning 2004; Johansen et al. 2007).”
FORMATION OF KUIPER BELT BINARIES BY GRAVITATIONAL COLLAPSE (2010, methodology): “We do not attempt to extract our initial data from the Johansen et al. (2007, 2009) simulations because they have low resolution (<10 grid cells) across the densest clumps.”
The minimum-mass extrasolar nebula: in situ formation of close-in super-Earths (2012, background): “Recent work focuses on a combination of aerodynamic and gravitational instabilities to agglomerate particles (Youdin & Goodman 2005; Johansen et al. 2007; Bai & Stone 2010; and references therein) — or on pure gravitational instability of a vertically thin and dense dust layer (Lee et al. 2010a,b;…”
The Disk Substructures at High Angular Resolution Project (DSHARP). VI. Dust Trapping in Thin-ringed Protoplanetary Disks (2018, background): “Let us, for the purpose of the argument, assume that the streaming instability, and the related process of gravoturbulent planetesimal formation (Johansen et al. 2007), can indeed occur in a pressure bump.”
Dust Evolution and the Formation of Planetesimals (2016, background): “…instability (Balbus & Hawley 1991) show that large-scale variations in the strength of the turbulence lead to the spontaneous formation of pressure bumps at the largest scales of the turbulent flow (Johansen et al. 2007; Simon et al. 2012; Dittrich et al. 2013; Simon & Armitage 2014).”
Spectroastrometric Imaging of Molecular Gas within Protoplanetary Disk Gaps (2008, background): “Thus, the presence of “pressure bumps” in the disk may concentrate the densities of such “pebbles” and “boulders”, potentially leading to the formation of planetesimals (Johansen et al. 2007).”
The structure of protoplanetary discs around evolving young stars (2014, background): “The streaming instability can lead to formation of planetesimals as a first step in forming planetary embryos and planets (Johansen et al. 2007; Johansen & Youdin 2007; Bai & Stone 2010a,b).”
The effect of gas drag on the growth of protoplanets. Analytical expressions for the accretion of small bodies in laminar disks (2010, background): “In Johansen et al. (2007) a dense particle layer of St ∼ 1 boulders collapses into a Ceres-mass planet (R ∼ 500 km), that rapidly accretes the remaining boulders on timescales of perhaps 10 yr.”
Forming Planetesimals in Solar and Extrasolar Nebulae (2009, methodology): “Simulations that include the streaming instability (e.g., Johansen et al. 2007) find that particles moderately coupled to gas—having stopping times τs ≥ 0.1—clump strongly enough to undergo gravitational collapse.”
Rubble Pile Asteroids (2018, background): “…on various gas-disk processes related to turbulence and instabilities to quickly collapse swarms of the mm- to cm-sized particles that dominate the texture of most primitive meteorite samples and quickly form the much larger planetesimals (Cuzzi 2008, Johansen et al. 2007; Johansen et al. 2015).”
FORMATION OF THE TERRESTRIAL PLANETS FROM A NARROW ANNULUS (2009, background): “This can potentially be realized if radial migration of solid material generates particle pile-ups (Haghighipour & Boss 2003; Youdin & Chiang 2004; Johansen et al. 2007) at preferred locations in the disk.”
Why do protoplanetary disks appear not massive enough to form the known exoplanet population? (2018, background): “In scenarios like pebble accretion (e.g., Johansen et al. 2007; Johansen & Lambrechts 2017; Ormel 2017), for example, only a small fraction of the pebble flux is captured by growing planets (see Guillot et al. 2014).”
COLLISIONS BETWEEN GRAVITY-DOMINATED BODIES. I. OUTCOME REGIMES AND SCALING LAWS (2011, background): “Two processes have been proposed to form km to 100 km-scale initial planetesimals: turbulent concentration (Cuzzi et al. 2008) and streaming instabilities (Johansen et al. 2007).”
A simple model for the evolution of the dust population in protoplanetary disks (2012, background): “The evolution of the dust-to-gas ratio is important for theories of planetesimal formation (e.g., Johansen et al. 2007, 2011) and planet formation (see Klahr & Bodenheimer 2006; Lissauer & Stevenson 2007; Mordasini et al. 2009).”
Dynamics of pebbles in the vicinity of a growing planetary embryo: hydro-dynamical simulations (2012, methodology): “More specifically, this model builds on the recent planetesimal formation model (Youdin & Goodman 2005; Johansen et al. 2006, 2007, 2009) in which large planetesimals (with sizes from ∼100 up to ∼1000 km) form by the collapse of a self-gravitating clump of pebbles, concentrated to high densities by…”
Chondrites as samples of differentiated planetesimals (2009, background): “Although new models and observations indicate rapid accretion (Johansen et al., 2007), the accretion of planetesimals early in solar system history was certainly not instantaneous, as discussed in Ghosh et al.”
Building Terrestrial Planets (2012, background): “A new alternative to this ordered-growth process is that planetesimals form due to the collective gravity of massive swarms of small particles, concentrated at some locations (local maxima of the gas density distribution or inter-vortex regions, depending on particle sizes) by the turbulence of the ”