Abstract
Since the building blocks of the Galilean satellites likely experience the chemical interaction with H2O in the circum-jovian nebula, they would have strongly oxidized composition. Here we revisit the model of internal structure and composition of Io taking into account highly oxidized materials. For the solar mixture of major rock-forming elements, the mineral combination has been calculated taking the content of O as a parameter. The minerals are distributed to the crust, mantle and core. The moment of inertia factor is calculated from their mass ratio and average densities. The composition of Io that explains the average density has the core with magnetite (66 wt %) and troilite (32 wt%), mantle with pyroxene (Mg# = 97) and crust with MgSO4 (66 wt %) and feldspar (30 wt %). These spheres occupy 34, 43 and 24 wt % of the total mass of Io, respectively. We focus on the large amount of MgSO4 and calculate the chemical equilibrium of MgSO4=MgO+SO2+ 1/2 O2 in the circum-jovian nebula. The existence of MgSO4 existence requires a fractionated region with low-T, high-SO2 pressure in the circum-jovian nebula. We also discuss the thermal structure of Io and stability of MgSO4 in the crust.
