Magnetic Induction Responses of Jupiter's Ocean Moons Including Effects
from Adiabatic Convection
Abstract
Prior analyses of oceanic magnetic induction within Jupiter’s large icy
moons have assumed uniform electrical conductivity. However, the phase
and amplitude responses of the induced fields will be influenced by the
natural depth-dependence of the electrical conductivity. Here, we
examine the amplitudes and phase delays for magnetic diffusion in
modeled oceans of Europa, Ganymede, and Callisto. For spherically
symmetric configurations, we consider thermodynamically consistent
interior structures that include realistic electrical conductivity along
the oceans’ adiabatic temperature profiles. Conductances depend strongly
on salinity, especially in the large moons. The induction responses of
the adiabatic profiles differ from those of oceans with uniform
conductivity set to values at the ice–ocean interface, or to the mean
values of the adiabatic profile, by more than 10\% for
some signals. We also consider motionally induced magnetic fields
generated by convective fluid motions within the oceans, which might
optimistically be used to infer ocean flows or, pessimistically, act to
bias the ocean conductivity inversions. Our upper-bound scaling
estimates suggest this effect may be important at Europa and Ganymede,
with a negligible contribution at Callisto. Based on end-member ocean
compositions, we quantify the 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
thermodynamic and electrical conductivity measurements in fluids at low
temperature and to high salinity and pressure as well as modeling of
motional induction responses.