Using magnetic field observations from the Galilean moons to diagnose ocean properties

One of the most important realizations that planetary scientists have come to in the last 20 years is that in the search for potential habitability in our solar system, the focus need not only be on planetary bodies close to the Sun, where water on the surface is in liquid state. Based on Galileo and Cassini observations in the Jupiter and Saturn systems, there are many potential places in our solar system where sub-surface liquid water oceans may exist. JUICE magnetometer (J-MAG) measurements (such as those made by the magnetometers on the Galileo and Cassini spacecraft) enable an understanding to be gained of the interior structure of the icy moons of Jupiter, specifically those of Ganymede, Callisto and Europa. Of particular interest are knowledge of the depth at which the liquid oceans reside beneath their icy surfaces, the strength of any internal magnetic fields such as at Ganymede and the strength of any induced magnetic fields arising within these oceans. The primary science objectives of JUICE which will be constrained by the magnetic field observations and which drove the performance requirements of the J-MAG instrument include: At Ganymede: Characterization of the extent of the ocean and its relation to the deeper interior Characterization of the ice shell Characterization of the local environment and its interactions with the Jovian magnetosphere Description of the deep interior and magnetic field generation At Europa, further constrain the depth of the liquid ocean and its conductivity At Callisto, characterize the outer shells, including the ocean