Updated Interior Structure of Callisto From a Reanalysis of Galileo Data

Abstract The internal structure of Callisto has been a long‐standing question since the Galileo mission. Previous analyses suggested a largely undifferentiated interior. We present an updated interior structure for Callisto derived from a reanalysis of Galileo's Doppler tracking data using new signal processing techniques. We present two solutions: a ‘classic’ hydrostatic model and our favored model, which accounts for non‐hydrostatic contributions from major impact basins. The latter yields a normalized Moment of Inertia (MOI) of 0.345 0.005, lower than the canonical value. Combined with magnetic induction data, our interior modeling indicates Callisto is more differentiated than previously believed. Our results favor a ∼10–120 km thick ice shell, a ∼300 km subsurface ocean—assuming the ocean partly generates the magnetic induction response—and a large rocky core with low average density. This density indicates a chondritic composition with significant mass fraction of organics, suggesting an interior configuration similar to that of Titan.