Toward Planetesimals: Dense Chondrule Clumps in the Protoplanetary Nebula

By J. Cuzzi, R. Hogan, Karim Shariff. 2008

318 citations recorded by the source corpus.

We outline a scenario that traces a direct path from freely floating nebula particles to the first 10-100 km sized bodies in the terrestrial planet region, producing planetesimals that have properties matching those of primitive meteorite parent bodies. We call this “primary accretion.” The scenario draws on elements of previous work and introduces a new critical threshold for planetesimal formation. We presume the nebula to be weakly turbulent, which leads to dense concentrations of aerodynamically size-sorted particles that have properties similar to those observed in chondrites. The fractional volume of the nebula occupied by these dense zones or clumps obeys a probability distribution as a function of their density, and the densest concentrations have particle mass densities that are 100 times that of the gas. However, even these densest clumps are prevented by gas pressure from undergoing gravitational instability in the traditional sense (on a dynamical timescale). While in this state of arrested development, they are susceptible to disruption by the ram pressure of the differentially orbiting nebula gas. However, self-gravity can preserve sufficiently large and dense clumps from ram pressure disruption, allowing their entrained particles to sediment gently but inexorably toward their centers, producing 10-100 km “sandpile” planetesimals. Localized radial pressure fluctuations in the nebula, as well as interactions between differentially moving dense clumps, will also play a role that must be accounted for in future studies. The scenario is readily extended from meteorite parent bodies to primary accretion throughout the solar system.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/cd8f093dca39b14297dbd006012c893d24606013

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Citations in the corpus

VELOCITY-DEPENDENT CATASTROPHIC DISRUPTION CRITERIA FOR PLANETESIMALS (2009, background): “…coagulation of planetesimals larger than ∼1 km must have occurred in a dynamically cold environment; alternatively, planetesimal growth was aided by a noncollisional mechanism such as gravitational instabilities and/or turbulence (Goldreich & Ward 1973; Johansen et al. 2007; Cuzzi et al. 2008).”
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).”
Dust Evolution and the Formation of Planetesimals (2016, background): “We will not discuss here the turbulent concentration mechanism proposed by Cuzzi et al. (2008), where chondrule-sized particles are concentrated on the smallest scales of the turbulent flow, as the relevance of this mechanism for protoplanetary discs is still under exploration.”
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 ”
Turbulence in the TW Hya Disk (2018, background): “…of planetesimals through the concentration of the micron to cm sized grains (Barge & Sommeria 1995; Klahr & Henning 1997; Johansen et al. 2007; Cuzzi et al. 2008), while the efficient dust settling associated with weak turbulence is a key factor in the creation of planetesimals through the…”
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).”
Water delivery and giant impacts in the 'Grand Tack' scenario (2014, unknown): “The gas drag calculations assume a planetesimal diameter of 100 km, consistent with recent models of planetesimal formation (Johansen et al., 2007; Cuzzi et al., 2008).”
A Perspective from Extinct Radionuclides on a Young Stellar Object: The Sun and Its Accretion Disk (2011, background): “A second class of models (Chambers 2010, Cuzzi et al. 2008) considers millimeter-sized particles (i.e., of chondrule size) that can be concentrated in lowvorticity regions of a turbulent disk.”
THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, background): “It is assumed that very early in the evolution of the disk, planetesimals form quickly and rapidly grow to a size of 100 km, for example due to gravoturbulent formation (Johansen et al. 2007; Cuzzi et al. 2008; Johansen et al. 2011).”
Forming Planetesimals in Solar and Extrasolar Nebulae (2009, background): “Thus it normally experiences a headwind, except possibly where there are variations to the power-law descent of P (r), as considered at the end of §3.1.2.”
Debris disc stirring by secular perturbations from giant planets (2009, background): “Despite promising recent progress (e.g., Johansen et al. 2007; Cuzzi et al. 2008), the formation of planetesimals is still not fully understood, and so these initial conditions, although reasonable, are not rigorously justified.”