EXPLORING THE INTERIORS OF THE GALILEAN MOONS WITH A MAGNETOMETER

The magnetometer experiment on the Galileo spacecraft has provided valuable insights into the interiors of the four Galilean moons of Jupiter. One of the astonishing findings has been the discovery of a moderately strong magnetic field (equatorial surface strength ~750 nT) in the icy moon Ganymede. As a field of this magnitude cannot be generated by induced magnetization and is unlikely to have resulted from remanent magnetization, it is now generally believe that a dynamo operating in a metallic convecting core creates and maintains the field. The absence of magnetic fields in the two other icy moons, Europa and Callisto is equally intriguing. I will discuss current ideas on what makes these moons so different from Ganymede. I will also discuss the current status of our research on the presence or absence of magnetic field in the volcanic moon Io. Magnetic field observations from the vicinity of the three icy moons, Europa, Ganymede and Callisto have also revealed the presence of electromagnetic induction responses to the rotating field of Jupiter. It appears that global conducting regions (presumed to be salty liquid oceans) exist below the icy surfaces of these moons that conduct electricity and create the observed electromagnetic induction responses. I will present the latest modeling work on the induction signatures that supports the presence of thick liquid oceans in these moons. Finally, I will discuss our current understanding of the interior structures and the geological histories of these moons and speculate on how liquid oceans can be maintained over geological times in the three icy moons.