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Formation of the Galilean satellites in a gaseous nebula

Lunine, Jonathan I. and Stevenson, David J. (1982) Formation of the Galilean satellites in a gaseous nebula. Icarus, 52 (1). pp. 14-39. ISSN 0019-1035. doi:10.1016/0019-1035(82)90166-X.

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A model for Galilean satellite formation was analyzed in which the satellites accrete in the presence of a dense, gaseous disk-shaped nebula and rapidly form optically thick, gravitationally bound primordial atmospheres. Upper-bound temperatures expected during accretion lead to partially differentiated structures for both Ganymede and Callisto, although with Ganymede much more differentiated than Callisto. When allowance is made for the aerodynamic breaking of infalling planetesimal fragments, lower surface temperatures result, and the amount of partial differentiation of Callisto is small, possibly approaching zero for a narrow size distribution of infalling planetesimals. The model is chosen to be consistent with the observed densities of the Galilean satellites and our current understanding of Jupiter formation. The retention of ices more volatile than H_2O is considered but not modeled in detail. A nominal nebula of ∼0.1 Jupiter masses is constructed by consideration of likely surface density profiles and existing Jupiter collapse calculations. This nebula is optically thick (even if grain opacity is ignored) in both radial and vertical directions and has a temperature profile T ∼ 3600 (R_J/R), where R_J is Jupiter's radius and R is the radial distance in the disk midplane. Satellites accrete very rapidly (dynamical time scales being 10^2–10^4 years) and their optically thick gaseous envelopes are unable to eliminate the heat of accretion by radiation. Water-saturated, convective, adiabatic envelopes form, through which planetesimals fall, break up, and partially disseminate their mass. The resulting satellite surface temperatures during accretion are calculated. Possible implications of these models for the subsequent evolution of Ganymede and Callisto are explored and it is suggested that the extensive differentiation undergone by Ganymede may provide the right environment for subsequent resurfacing, whereas the relative lack of extensive differentiation for Callisto may explain the inferred absence of endogenic tectonism.

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Lunine, Jonathan I.0000-0003-2279-4131
Stevenson, David J.0000-0001-9432-7159
Additional Information:© 1982 by Academic Press. Inc. Received September 3, 1981; revised February 16, 1982. We thank T. Ahrens, A. J. Friedson, D. Jewitt, and E. Karle for helpful comments and suggestions. We are especially grateful to Pat Cassen for his careful review and criticism of an earlier version of the manuscript, as well as his encouragement to pursue these models. This work is supported by NASA Grant NAGW-185.
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Official Citation:Jonathan I. Lunine, David J. Stevenson, Formation of the galilean satellites in a gaseous nebula, Icarus, Volume 52, Issue 1, October 1982, Pages 14-39, ISSN 0019-1035,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39097
Deposited By: Tony Diaz
Deposited On:26 Jun 2013 17:49
Last Modified:09 Nov 2021 23:42

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