Shapes, masses and interiors of satellites

Abstract

Limb-fitting methods applied to Voyager images of the satellites of Saturn have shown that some of these satellites are well-represented by triaxial ellipsoids. Furthermore, the observed ratios of the differences of the principal axes of these satellites are consistent with those values expected for synchronous satellites in hydrostatic equilibrium. For satellites of known mass, measurement of the shape leads to a determination of the satellite's moment of inertia and internal structure. The moment of inertia of Mimas determined by Dermott and Thomas ( Icarus, 73, 25–65, 1988) shows clearly that Mimas is not homogeneous. For satellites of unknown mass, but known mantle composition, measurement of the shape can lead to a determination of the satellite's mass and mean density. This method has been successfully applied to Enceladus.