Particle-Gas Dynamics in the Midplane of a Protoplanetary Nebula

Cuzzi, Jeffrey N.; Dobrovolskis, Anthony R.; Champney, Joelle M.

doi:10.1006/icar.1993.1161

Cited by 421 publications

(449 citation statements)

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“…These general arguments are supported by numerical simulations (Cuzzi, Dobrovolskis, & Champney 1993) that calculate the steady state properties of two-phase (gas and particulate) turbulence in the midplane of a MSN disk.…”

Section: Introductionmentioning

confidence: 69%

Planetesimal Formation by Gravitational Instability

Youdin

Shu

2002

ApJ

462

465

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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 Â 10 6 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.

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Section: Introductionmentioning

confidence: 69%

Planetesimal Formation by Gravitational Instability

Youdin

Shu

2002

ApJ

462

465

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“…But at late times, the dust density outside the thin, dense dust layer is likely to be quite small, decreasing the dust-to-gas ratio there. Inside the dust layer, however, solids may dominate the local density (Cuzzi, Dobrovolskis, & Champney 1993). Hence, % 50 may be reached in the midplane, where most solids reside.…”

Section: Energy Equations and Chondrule Formationmentioning

confidence: 99%

Chondrule Formation and Protoplanetary Disk Heating by Current Sheets in Nonideal Magnetohydrodynamic Turbulence

Joung¹,

Low²,

Ebel³

2004

ApJ

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We study magnetic field steepening due to ambipolar diffusion in protoplanetary disk environments and draw the following conclusions. Current sheets are generated in magnetically active regions of the disk where the ionization fraction is high enough for the magnetorotational instability to operate. In late stages of solar nebula evolution, the surface density is expected to decrease and dust grains are expected to gravitationally settle to the midplane. If the local dust-to-gas mass ratio near the midplane is increased above cosmic abundances by factors k10 3 , current sheets reach high enough temperatures to melt millimeter-sized dust grains and hence may provide the mechanism to form meteoritic chondrules. In addition, these current sheets possibly explain the near-infrared excesses observed in spectral energy distributions (SEDs) of young stellar objects. Direct imaging of protoplanetary disks via a nulling interferometer or, in the future, a multiband, adaptive optics coronagraph can test this hypothesis.

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“…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 discs.Planet formation models typically treat turbulence as a diffusive process that opposes the gravitational sedimentation of solids to a high density midplane layer in circumstellar discs 7,13 . Recent models of solids moving in turbulent gas reveal that the turbulent motions not only mix them, but also concentrate metre-sized boulders in the transient gas overdensities 9 formed in magnetorotational turbulence 14 , in giant gaseous vortices 15,16 , and in spiral arms of self-gravitating discs 17 .…”

mentioning

confidence: 99%

“…A sedimentary midplane layer forms with a width determined by a balance between settling and turbulent diffusion 7,13 .…”

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confidence: 99%

Rapid planetesimal formation in turbulent circumstellar disks

Johansen

Oishi

Low

et al. 2007

Nature

1,117

977

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The initial stages of planet formation in circumstellar gas discs proceed via dust grains that collide and build up larger and larger bodies 1 . How this process continues from metre-sized boulders to kilometre-scale planetesimals is a major unsolved problem 2 : boulders stick together poorly 3 , and spiral into the protostar in a few hundred orbits due to a head wind from the slower rotating gas 4 . Gravitational collapse of the solid component has been suggested to overcome this barrier 1,5,6 . Even low levels of turbulence, however, inhibit sedimentation of solids to a sufficiently dense midplane layer 2, 7 , but turbulence must be present to explain observed gas accretion in protostellar discs 8 . Here we report the discovery of efficient gravitational collapse of boulders in locally overdense regions in the midplane. The boulders concentrate initially in transient high pressures in the turbulent gas 9 , and these concentra-1 arXiv:0708.3890v1 [astro-ph] 29 Aug 2007 tions are augmented a further order of magnitude by a streaming instability [10][11][12] 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 discs.Planet formation models typically treat turbulence as a diffusive process that opposes the gravitational sedimentation of solids to a high density midplane layer in circumstellar discs 7,13 . Recent models of solids moving in turbulent gas reveal that the turbulent motions not only mix them, but also concentrate metre-sized boulders in the transient gas overdensities 9 formed in magnetorotational turbulence 14 , in giant gaseous vortices 15,16 , and in spiral arms of self-gravitating discs 17 .Short-lived eddies at the dissipation scale of forced turbulence concentrate smaller millimetre-sized solids 18 . Some simulations mentioned above 9,11,12 were performed with the Pencil Code, which solves the magnetohydrodynamic (MHD) equations on a three-dimensional grid for a gas that interacts through drag forces with boulders. Boulders are represented as superparticles with independent positions and velocities, each having the mass of a huge number of boulders but the aerodynamic behaviour of a single boulder. We have now further developed the Pencil Code to include a fully parallel solver for the gravitational potential of the particles (see Supplementary Information). The particle density is mapped on the grid using the Triangular Shaped Cloud assignment scheme 19 and the gravitational potential of the solids is found using a Fast Fourier Transform method 20 . 2This allows us, for the first time, to simulate the dynamics of self-gravitating solid particles in magnetised, three-dimensional turbulence.We model a corotating, local box with linearised Keplerian shear that straddles the protoplanetary disc midplane and orbits the young star ...

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Particle-Gas Dynamics in the Midplane of a Protoplanetary Nebula

Cited by 421 publications

References 50 publications

Planetesimal Formation by Gravitational Instability

Planetesimal Formation by Gravitational Instability

Chondrule Formation and Protoplanetary Disk Heating by Current Sheets in Nonideal Magnetohydrodynamic Turbulence

Rapid planetesimal formation in turbulent circumstellar disks

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