The shape and internal structure of Mimas

Abstract

The present effort to determine the shape of Mimas proceeds on the basis of limb profiles from six Voyager images; the fitting of ellipses to the limbs indicates that the shape is a triaxial ellipsoid. The satellite mass determined by Kozai (1957), in conjunction with a second-order theory for the ellipsoidal figure of equilibrium, leads to a satellite mean radius determination of 198.8 + or - 0.6 km, and a mean density of 1.137 + or - 0.018 g/cu cm. It is suggested that Mimas is probably differentiated, with a rocky core and a water-ice crust; alternatively, Mimas has a cosmic composition of ice and rock and is undifferentiated.