Article,
Subsurface oceans on Europa and Callisto: Constraints from Galileo magnetometer observations
Icarus, 147 (2): 329--347 (2000)
Abstract
Magnetic field perturbations measured during Galileo flybys of Europa
and Callisto are consistent with dipole fields induced by the temporal
variations of the ambient jovian magnetospheric field. These fields
are close to these expected for perfectly conducting moons. We investigate
the implications of these observations for the electrical structure
of the moon's interiors using a simple shell model. It is found that
Europa and Callisto must possess regions where the conductivity exceeds
0.06 and 0.02 S/m at a depth of less than 200 and 300 km below the
surface, respectively. This conductivity is unattainable in ice or
silicates, unless the ice layer is at least partially molten or very
large temperature gradients can be maintained below the ice. An ionosphere
or a cloud of pick-up ions are probably also insufficiently conductive.
Global Earth-like oceans under the surface of both moons could account
for the observations provided they are at least a few kilometers
thick. (C) 2000 Academic Press.
