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Three-layered models of Ganymede and Callisto: Compositions, structures, and aspects of evolution

Mueller, Steve ; McKinnon, William B.

Icarus (New York, N.Y. 1962), 1988-12, Vol.76 (3), p.437-464 [Periódico revisado por pares]

Legacy CDMS: Elsevier Inc

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  • Título:
    Three-layered models of Ganymede and Callisto: Compositions, structures, and aspects of evolution
  • Autor: Mueller, Steve ; McKinnon, William B.
  • Assuntos: 640107 - Astrophysics & Cosmology- Planetary Phenomena ; Astrophysics ; CHEMICAL COMPOSITION ; CHONDRITES ; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS ; Cosmochemistry. Extraterrestrial geology ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Extraterrestrial geology ; HEATING ; JUPITER PLANET ; MATHEMATICAL MODELS ; METEORITES ; MINERALOGY ; MORPHOLOGY ; PLANETARY EVOLUTION ; PLANETS ; RHEOLOGY ; ROCKS ; SATELLITES ; SOLAR SYSTEM EVOLUTION ; STONE METEORITES
  • É parte de: Icarus (New York, N.Y. 1962), 1988-12, Vol.76 (3), p.437-464
  • Notas: CDMS
    Legacy CDMS
    ObjectType-Article-2
    SourceType-Scholarly Journals-1
    ObjectType-Feature-1
    content type line 23
  • Descrição: Three-layered structural models are determined for Ganymede and Callisto. Each consists of a rock core, a mixed ice-rock lower mantle, and a pure ice upper mantle. This structure results from differentiation subsequent to accretional melting. Attention is given to evaluating various candidates for the rock component and three alternatives, representing various degrees of silicate hydration and oxidation, are modeled and incorporated. Structures are calculated on the basis of a 250°K isotherm, which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites. Differentiation of an ice-rock satellite generally involves an increase in radius, and the three-layered approach allows this process to be examined in some detail. It is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion. If tectonics are due to global expansion, distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult. The postaccretional global expansion of Ganymede, which may have left a tectonic record, was probably limited to 1% in radius, in agreement with observed limits. Useful quantities such as silicate mass and volume fraction, uncompressed density, J 2, C 22, binding energy, and surface heat flow are also determined. Nonhydrostatic contributions to J 2 and C 22 are estimated and shown to be nonnegligible. Encounters with Jupiter-orbiting spacecraft are unlikely to determine Callisto's degree of central condensation. We conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating. Three-layered satellites have generally hotter interiors, because additional thermal boundary layers divide the separately convecting upper and lower mantles, inhibiting heat transport. Ganymedes and Callistos that are less than about 1 3 differentiated (by mass) should experience a second episode of melting, as these boundary layers are either above the level of the water-ice minimum-melting temperature or intersect the melting curve at deeper levels. Runaway differentiation to at least a depth corresponding to a pressure in the ice V stability field is likely. The main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath (as in the instability following ocean closure of Kirk and Stevenson), moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics (as in Callisto), because extensive differentiation ultimately occurs.
  • Editor: Legacy CDMS: Elsevier Inc
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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