Van der Voo Lecture - Mark Simons, Caltech

Saturn’s moon Enceladus is a primary target for the investigation of habitability elsewhere in our Solar System. This small moon is inferred to have an extensive body of water beneath its outer ice shell - at least below the South Polar Terrain (SPT). This inference is based on the observations of active jets feeding a large plume emanating from the SPT, the detection of salts and silica particles in plume material and Saturn’s E-ring, and the variations in geology seen between regions within and outside of the SPT. The amplitude of forced libration experienced by Enceladus requires mechanical decoupling of the ice shell from the underlying core, which in turn has been interpreted to require a global ocean underlying the ice crust. We explore an alternative interpretation that does not include a global ocean but remains consistent with the observed libration and the gravity observations. The observed gravity field is consistent with a thinning of the ice crust at the SPT underlain by a confined regional sea. Jet activity on Enceladus is documented to be modulated by the tides as Enceladus orbits around Saturn, which we propose is driven by the interplay of strike slip motion on the Tiger Stripes with geometric complexities in these fault systems. The importance of geophysical exploration of Enceladus to understand habitability is clear. We discuss a variety of modern geodetic techniques that should be considered in formulating future missions to this fascinating moon.