Planetesimals to planets: Numerical simulation of collisional evolution

Greenberg, R.; Wacker, J. F.; Hartmann, W. K.; Chapman, C. R.

doi:10.1016/0019-1035(78)90057-x

Cited by 449 publications

(304 citation statements)

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“…The crucial parameter for this stage is the encounter velocity between impacting objects, which has to be lower than the bodies escape velocity (corrected by an energy dissipation factor) in order to allow mutual accretion. In a gravitationally unperturbed disk, this condition is met for a large fraction of mutual impacts (e.g Safronov 1969;Greenberg et al 1978), but external gravitational perturbations might lead to relative velocity increase and thus inhibit accretion. Such a risk obviously exists in a binary system, where the companion star affects the inner disk through secular perturbations leading to substantial eccentricity oscillations (e.g.…”

Section: Introductionmentioning

confidence: 99%

Relative velocities among accreting planetesimals in binary systems: The circumprimary case

Thébault

Marzari

Scholl

2006

Icarus

158

294

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We investigate classical planetesimal accretion in a binary star system of separation a b ≤50 AU by numerical simulations, with particular focus on the region at a distance of 1 AU from the primary. The planetesimals orbit the primary, are perturbed by the companion and are in addition subjected to a gas drag force. We concentrate on the problem of relative velocities ∆v among planetesimals of different sizes. For various stellar mass ratios and binary orbital parameters we determine regions where ∆v exceed planetesimal escape velocities v esc (thus preventing runaway accretion) or even the threshold velocity v ero for which erosion dominates accretion. Gaseous friction has two crucial effects on the velocity distribution: it damps secular perturbations by forcing periastron alignment of orbits, but at the same time the size-dependence of this orbital alignment induces a significant ∆v increase between bodies of different sizes. This differential phasing effect proves very efficient and almost always increases ∆v to values preventing runaway accretion, except in a narrow e b ≃ 0 domain. The erosion threshold ∆v > v ero is reached in a wide (a b , e b ) space for small < 10 km planetesimals, but in a much more limited region for bigger ≃ 50 km objects. In the intermediate v esc < ∆v < v ero domain, a possible growth mode would be the type II runaway growth identified by Kortenkamp et al. (2001).

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Section: Introductionmentioning

confidence: 99%

Relative velocities among accreting planetesimals in binary systems: The circumprimary case

Thébault

Marzari

Scholl

2006

Icarus

158

294

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“…It is now generally accepted that the formation of the terrestrial planets and smaller bodies in the solar system occurred via a grain accumulation process (see Safronov, 1969;Hartmann, 1978;Greenberg et al, 1978;Wetherill, 1980). The basis for this conclusion is the depletion of the noble gases Ne, Ar, Kr, and Xe compared with elements forming condensible molecules of equivalent molecular weight (Russell and Menzel, 1933;H.…”

Section: Accumulation From Solid Grainsmentioning

confidence: 99%

“…Making use of the behavior of snow deposits, the authors suggested that these aggregates would grow into low-density, kilometer-sized cometary nuclei. This model was later modified (Donn, 1981) to take into account the development of a size distribution of planetesimals in theories of planet accumulation (Safronov, 1969;Wetherill, 1980;R. Greenberg et al, 1978).…”

Section: Survey Of Processes For Comet Accumulationmentioning

confidence: 99%

“…Greenberg et al (1978) treated the case of planet formation in the region of Uranus and Neptune, starting with planetesimals produced by the Goldreich and Ward (1973) mechanism. For the accumulation of terrestrial planets, 1-km objects were the starting material.…”

Section: Survey Of Processes For Comet Accumulationmentioning

confidence: 99%

“…For the region of Neptune, Goldreich and Ward's (1973) theory yields initial objects about 100 km in diameter. Greenberg et al (1978) suggested that coagulation and nonhomologous settling of grains to the mid-plane could cause smaller regions of instability to develop before all material settled out, thus producing a distribution of kilometer-sized aggregates. The authors proposed these initial objects to be the comets that were ejected into the Oort Cloud.…”

Section: Survey Of Processes For Comet Accumulationmentioning

confidence: 99%

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The Accumulation and Structure of Comets

Donn¹

1989

International Astronomical Union Colloquium

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ABSTRACT. The evidence for the accumulation of the terrestrial planets and comets from solid grains is reviewed briefly. The various proposals for formation of cometary nuclei are described and commented upon. With three exceptions, all hypotheses conclude or imply that a single compact object forms. It has been almost universally assumed that grain accretion produced compact aggregates as is the case with liquid drops, and that this process continued. Several hypotheses start with Goldreich-Ward-type gravitational instabilities. The collapse for this case also occurs at low velocities in the cm-s -1 to ms _ 1 range. Experiment and theory show that under these conditions, low-density, filamentary clusters form that are fractal aggregates with a fractal dimension approximately equal to two. Agglomeration of these clusters produces larger, compressible planetesimals or cometesimals, which efficiently combine upon colliding. In order to form cometary nuclei, the initial temperature must be about 50 K and not undergo a significant temperature rise during the accumulation process. The collision process can be analyzed with some simplifying assumptions using the limited experimental data available for the compaction of low-density powders. The calculations show that accumulation will occur at low temperatures. For a more refined analysis, experiments to study impacts on low-density powders are required. Models of cometary nuclei are reviewed, and a simple model of the structure that results from the accumulation of fluffy aggregates is described.1 .

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