Thomas, P. C., Helfenstein, P., Veverka, J., Burns, J., Porco, C., Denk, T., Turtle, E. (2006). "Sizes, shapes, relaxation states, and interior configurations of icy Saturnian satellites." American Astronomical Society, DPS meeting #38, #69.02.


Abstract
The sizes and shapes of six icy Saturnian satellites have been measured from Cassini Imaging Science Subsystem (ISS) data. Mimas, Enceladus, Tethys, Dioneand Rhea are well described by triaxial ellipsoids, Iapetus is best represented by an oblate spheroid. All satellites appear to have approachedrelaxed, equilibrium shapes at some point in their evolution, but all support at least 300 m of global-wavelength topography. The shape and mean density ofEnceladus suggest that if it is differentiated it has a large, low-density core, the core itself may have inhomogeneities in density or shape, and anouter ice shell may be laterally inhomogeneous in density. Fully relaxed, radially differentiated, laterally-homogeneous models do not explain the shapeof Enceladus. Iapetus' global shape supports a fossil bulge of over 30 km (distinct from the equatorial ridge, which has little effect on global shape),and provides a benchmark for cratering modification after global relaxation.