Magnetic Induction in Convecting Galilean Oceans

Abstract

To date, analyses of magnetic induction in putative oceans in Jupiter's large icy moons have assumed uniform conductivity in the modeled oceans. However, the phase and amplitude response of the induced fields will be influenced by the increasing electrical conductivity along oceans' convective adiabatic temperature profiles. Here, we examine the amplitudes and phase lags for magnetic diffusion in modeled oceans of Europa, Ganymede, and Callisto. We restrict our analysis to spherically symmetric configurations, treating interior structures based on self-consistent thermodynamics, which account for variations in electrical conductivity with depth in convective oceans (Vance et al., 2018). The numerical approach considers tens of radial layers. The induction response of the adiabatic conductivity profile differs from oceans with uniform conductivity based on the ice-ocean interface or the mean value of the adiabatic profile by more than 10% in many cases. In addition, we consider the generation of induced magnetic fields by oceanic fluid motions that might be used to probe the ocean flows directly (e.g., Chave, 1983; Tyler, 2011; Minami, 2017). Assuming turbulent convection (Soderlund et al., 2014), we find that these signals can dominate induction signal at low latitudes, which underscores the need for spatial coverage in magnetic induction investigations. Based on end-member ocean compositions (Zolotov, 2008; Zolotov & Kargel, 2009), we quantify the residual magnetic induction signals that might be used to infer the oxidation state of Europa's ocean and to investigate stable liquids within and under high-pressure ices in Ganymede and Callisto. Fully exploring this parameter space for the sake of planned missions requires electrical conductivity measurements in fluids at low temperature and to high salinity and pressure.