Induced Magnetic Field from Europa's Subsurface Ocean
The animation shows the geometry of the magnetic field created within Europa’s subsurface ocean as Europa moves through Jupiter’s magnetic field, which varies in strength and direction at Europa as it orbits Jupiter. Jupiter’s magnetic field creates a response within Europa’s ocean at two fundamental timescales. First, Jupiter’s magnetic field is tilted at a 10-degree angle from the planet’s rotation axis, and this results in magnetic field variations on Europa on a timescale of 11 hours, which is Jupiter’s rotation period with respect to Europa. Second, the plane in which Europa orbits Jupiter is slightly tilted with respect to Jupiter’s equator, and is somewhat offset from the center of Jupiter. Europa orbits Jupiter every 85 hours, and the variation in distance from Jupiter also produces a variation in the magnetic field that Europa feels on this timescale. These regularly varying magnetic field signatures drive electrical currents within Europa’s salty ocean, which is located underneath an icy shell. The electrical ocean currents in turn produce “induced” magnetic fields with a geometry shown in green for the 11-hour period and cyan for the 85-hour period. Europa Clipper will measure the induced magnetic field at Europa, for many different locations of Europa within Jupiter’s magnetic field, both in time and space. From these measurements, scientists can determine the thickness of the ice shell and ocean and the conductivity of the ocean. The conductivity provides an estimate for the salinity of the ocean, which is a key indicator of Europa’s habitability.