CHEMICAL DIFFERENTIATION OF THE GALILEAN SATELLITES OF JUPITER: 4. ISOCHEMICAL MODELS FOR THE COMPOSITIONS OF IO, EUROPA, AND GANYMEDE

Abstract

Models for the composition and structure of the Galilean satellites of Jupiter (Io, Europa, and Ganymede) were constructed using geophysical data provided by the Galileo mission on the mass, average density, and moment of inertia, as well as thermodynamic data on the equation of the state of water, high-pressure ices, and meteoritic materials. The distribution of density, pressure, temperature, and gravity acceleration in the interiors of the satellites was determined. A simulation of the internal structure of the satellites showed the possibility of identical bulk compositions for water-free Io and the rock-iron cores of Europa and Ganymede (i.e., satellites without their outer ice-water shells). The sizes of the satellites' cores (Fe with 10 wt % S) and the thicknesses of the ice-water shells of Europa (120 km) and Ganymede (900 km) were also estimated. These satellites contain 7 and 47% H2 O, respectively. The radii of Fe-10% S cores are 737 km for Io, 695 km for Ganymede, and 576 km for Europa. The ratios of the radii and masses of the Fe-S scores and rock-iron cores of Io, Ganymede, and Europa are almost identical and equal R (Fe-10%S core)/R Cor = 0.4 and M (Fe-10% S core)/M Cor = 10.55 ± 0.3 wt %. It was shown that the geochemical parameters of the rock-iron constituent of the satellites are similar to the material of L/LL chondrites. The silicate fraction of the satellites contains about 16 wt % FeO and shows an Fe/Si mass ratio of 0.53. The total iron to silicon mass ratio is also identical in the three satellites: (Fetot/Si)Cor = 0.99 ± 0.02. This value is different from that in the bulk compositions of the most oxidized carbonaceous chondrites and the most reduced H chondrites. Io, Europa, and Ganymede could be formed in the accretion disk of Jupiter from a material similar to L/LL chondrites under relatively low temperatures, not higher than the evaporation temperature of Fe and Fe-Mg silicates. © Pleiades Publishing, Inc. 2006.