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Planet formation by coagulation: A focus on Uranus and Neptune

Goldreich, Peter and Lithwick, Yoram and Sari, Re'em (2004) Planet formation by coagulation: A focus on Uranus and Neptune. Annual Review of Astronomy and Astrophysics, 42 . pp. 549-601. ISSN 0066-4146.

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Planets form in the circumstellar disks of young stars. We review the basic physical processes by which solid bodies accrete each other and alter each others' random velocities, and we provide order-of-magnitude derivations for the rates of these processes. We discuss and exercise the two-groups approximation, a simple yet powerful technique for solving the evolution equations for protoplanet growth. We describe orderly, runaway, neutral, and oligarchic growth. We also delineate die conditions under which each occurs. We refute a popular misconception by showing that the outer planets formed quickly by accreting small bodies. Then we address the final stages of planet formation. Oligarchy ends when the surface density of the oligarchs becomes comparable to that of the small bodies. Dynamical friction is no longer able to balance viscous stirring and the oligarchs' random velocities increase. In the inner-planet system, oligarchs collide and coalesce. In the outer-planet system, some of the oligarchs are ejected. In both the inner- and outer-planet systems, this stage ends once the number of big bodies has been reduced to the point that their mutual interactions no longer produce large-scale chaos. Subsequently, dynamical friction by the residual small bodies circularizes and flattens their orbits. The final stage of planet formation involves the clean up of the residual small bodies. Clean up has been poorly explored.

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Sari, Re'em0000-0002-1084-3656
Additional Information:© 2004 Annual Reviews. First published online as a Review in Advance on June 2, 2004. We thank M. Brown, E. Chiang, L. Dones, M. Duncan, J. Goodman, S. Ida, S. Kenyon, E. Kokubo, J. Makino, N. Murray, R. Rafikov, D. Stevenson, E. Thommes, S. Tremaine, and A. Youdin for useful discussions. This research was supported in part by NSF grants AST-0098301 and PHY-0070928 and by NASA grant NAG5-12037.
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Subject Keywords:planets, Solar System, runaway, accretion, oligarchy
Record Number:CaltechAUTHORS:GOLaraa04
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Official Citation:Planet Formation by Coagulation: A Focus on Uranus and Neptune. Peter Goldreich, Yoram Lithwick, and Re'em Sari. Annual Review of Astronomy and Astrophysics 2004 42:1, 549-601; doi: 10.1146/annurev.astro.42.053102.134004
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1019
Deposited By: Tony Diaz
Deposited On:01 Dec 2005
Last Modified:15 Jan 2020 22:17

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