Accumulation of Chondrules on Asteroids

Whipple, Fred L.

doi:10.1017/s0252921100089107

Cited by 18 publications

(6 citation statements)

References 8 publications

(9 reference statements)

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“…We have not specifically addressed the question of how the chondrules and metal grains acquired their dimensions. It is possible that aerodynamic sorting occurred in a fashion similar to that described here, as discussed by many authors [Whipple, 1971[Whipple, , 1972Dodd, 1976;Rubin and Keil, 1984;Leenhouts and Skinner, 1991;Leenhouts, 1991, 1993a, b;Haack and Scott, 1993;Scott and Haack, 1993]. However, there is also the possibility that the present size distributions of the chondrules and the metal grains are a primary property acquired during formation.…”

Section: Metal and Chondrule Size Distributionssupporting

confidence: 58%

Metal‐silicate fractionation in the surface dust layers of accreting planetesimals: Implications for the formation of ordinary chondrites and the nature of asteroid surfaces

Huang¹,

Akridge²,

Sears³

1996

J. Geophys. Res.

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Some of the most primitive solar system materials available for study in the laboratory are the ordinary chondrites, the largest meteorite class. The size and distribution of the chondrules (silicate beads) and metal, which leads to the definition of the H, L, and LL classes, suggest sorting before or during aggregation. We suggest that meteorite parent bodies (probably asteroids) had thick dusty surfaces during their early evolution that were easily mobilized by gases evolving from their interiors. Density and size sorting would have occurred in the surface layers as the upward drag forces of the gases (mainly water) acted against the downward force of gravity. The process is analogous to the industrially important process of fluidization and sorting in pyroclastic volcanics. We calculate that gas flow velocities and gas fluxes for the regolith of an asteroid‐sized object heated by the impact of accreting objects or by 26Al would have been sufficient for fluidization. It can also explain, quantitatively in some cases, the observed metal‐silicate sorting of ordinary chondrites, which has long been ascribed to processes occurring in the primordial solar nebula. Formation of the chondrites in the thick dynamic regolith is consistent with the major properties of chondritic meteorites (i.e., redox state, petrologic type, cooling rate, matrix abundance). These ideas have implications for the nature of asteroid surfaces and the virtual lack of asteroids with ordinary chondrite‐like surfaces.

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Section: Metal and Chondrule Size Distributionssupporting

confidence: 58%

Metal‐silicate fractionation in the surface dust layers of accreting planetesimals: Implications for the formation of ordinary chondrites and the nature of asteroid surfaces

Huang¹,

Akridge²,

Sears³

1996

J. Geophys. Res.

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“…This would favor low‐speed accretion of chondrules by asteroid‐sized bodies rather than planetary embryos. In addition, aerodynamic sorting during later encounters with nonresonant asteroid‐sized bodies may have further enhanced chondrule accretion by those bodies, as suggested originally by Whipple (1971, 1972). Specifically, smaller (e.g., <0.1 mm sized) particles, would have been preferentially swept around the accreting planetesimal by the subsonic nebular gas flow while larger chondrule‐sized particles would have accreted.…”

Section: Conclusion and Discussionmentioning

confidence: 85%

The planetesimal bow shock model for chondrule formation: A more quantitative assessment of the standard (fixed Jupiter) case

Hood

Weidenschilling

2012

Meteorit & Planetary Scien

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Abstract-One transient heating mechanism that can potentially explain the formation of most meteoritic chondrules 1-3 Myr after CAIs is shock waves produced by planetary embryos perturbed into eccentric orbits via resonances with Jupiter following its formation. The mechanism includes both bow shocks upstream of resonant bodies and impact vapor plume shocks produced by high-velocity collisions of the embryos with small nonresonant planetesimals. Here, we investigate the efficiency of both shock processes using an improved planetesimal accretion and orbital evolution code together with previous simulations of vapor plume expansion in the nebula. Only the standard version of the model (with Jupiter assumed to have its present semimajor axis and eccentricity) is considered. After several hundred thousand years of integration time, about 4-5% of remaining embryos have eccentricities greater than about 0.33 and shock velocities at 3 AU exceeding 6 km s )1 , currently considered to be a minimum for melting submillimeter-sized silicate precursors in bow shocks. Most embryos perturbed into highly eccentric orbits are relatively large-half as large as the Moon or larger. Bodies of this size could yield chondrule-cooling rates during bow shock passage compatible with furnace experiment results. The cumulative area of the midplane that would be traversed by highly eccentric embryos and their associated bow shocks over a period of 1-2 Myr is <1% of the total area. However, future simulations that consider a radially migrating Jupiter and alternate initial distributions of the planetesimal swarm may yield higher efficiencies.

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“…This formulation damps the eccentricity and inclination to zero on the relevant friction time-scale, with the term v + ∆v in v g corresponding to an orbitally averaged relative speed which would enter equation (29). We have checked the analytical evolution of e and i against an N -body integration of an eccentric orbit circularised by gas drag and found excellent agreement.…”

Section: Eccentricity Damping By Gas Drag and Chondrule Accretionmentioning

confidence: 88%

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

et al. 2015

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Accumulation of Chondrules on Asteroids

Cited by 18 publications

References 8 publications

Metal‐silicate fractionation in the surface dust layers of accreting planetesimals: Implications for the formation of ordinary chondrites and the nature of asteroid surfaces

Metal‐silicate fractionation in the surface dust layers of accreting planetesimals: Implications for the formation of ordinary chondrites and the nature of asteroid surfaces

The planetesimal bow shock model for chondrule formation: A more quantitative assessment of the standard (fixed Jupiter) case

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

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