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, accounting for variations in electrical
conductivity with depth in convective oceans
\citep{Vance_2018}. The numerical approach considers
tens of radial layers. The induction response of the adiabatic
conductivity profile differs from that of an ocean with uniform
conductivity set to that at the ice-ocean interface, or to the mean
value of the adiabatic profile, by more than 10\% in
many cases. We compare these modeled signals with magnetic fields
induced by oceanic fluid motions that might be used to measure oceanic
flows
\citep[e.g.,][]{Chave83,Tyler11,Minami17}. For
turbulent convection \citep{soderlund2014ocean}, we
find that these signals can dominate induction signal at low latitudes,
underscoring the need for spatial coverage in magnetic investigations.
Based on end-member ocean compositions
\citep{zolotov2008oceanic,zolotov2009chemical}, 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 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.