Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p12c..07m&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P12C-07
Physics
5417 Gravitational Fields (1227), 5430 Interiors (8147), 5440 Magnetic Fields And Magnetism, 5455 Origin And Evolution, 6218 Jovian Satellites
Scientific paper
Accurate densities and moments-of-inertia for the Galilean satellites provide powerful constraints on primary interior characteristics, but are inadequate to determine important next-level features, such as the Fe/Si ratio, without ancillary assumptions. These include cosmochemical, geochemical, and geophysical constraints. The Galilean satellites formed in the jovian subnebula, which is a late byproduct of Jupiter's growth in the solar nebula. Solid materials at Jupiter's position, well beyond the solar nebula "snow line," were ice rich and are best represented today by dark, presumably carbonaceous asteroids of the outer belt and Trojan clouds, types C, P, and especially D. In traditional (minimum-mass) models of the jovian subnebula, heating and thermochemical requilibration of these materials imply accretion of oxidized and hydrated minerals (e.g., serpentine and magnetite). New, gas-starved disk models provide heating but much less opportunity for thermochemistry, so direct incorporation of anhydrous minerals and free metal, for example, should be possible, although oxidation and hydration may still occur within the satellites. Metallic core formation in Io, Europa, and Ganymede did not occur as in the inner solar system, through massive accretional heating and/or early intense radiogenic heating due to 26Al, because of smaller body sizes, buffering by ice melting, and later accretion times for the satellites. Rather, once rock from ice (water) differentiation occurred, metallic core formation would have occurred in classic Elsasser style, driven by long-lived radiogenic, and if available, tidal heating. If free iron were available, Fe-FeS eutectic melting would occur, but core formation would be inefficient because of surface tension effects, unless convective temperatures were overdriven by tidal heating; nevertheless, metal would remain in the mantles. In contrast, if the rock+metal interiors were oxidized, eutectic melting would occur along the FeS-Fe3O4 join. Experiments indicate that the higher oxidation state relieves the surface tension constraint, and core formation would be efficient, and the cores formed would be relatively low density (S and O rich). Rock+metal interiors containing only FeS metal (with the remaining Fe in silicates) cannot form cores.
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