Orbital inclination of Iapetus and the rotation of the Laplacian plane

Abstract

This paper explores the possibility that the orbit of Iapetus, with its relatively large inclination but small eccentricity, was generated by a rapid dispersal of a gaseous circumplanetary disk, assumed to be the progenitor of the satellite system. The orientation of the local Laplacian plane is shown to be a sensitive function of the disk's structure. Modification of the disk on a time scale comparable to the precesion of the orbit's nodal line, [i.e., O (10 2−10 3 years)], can produce a large inclination from one that is initially zero, while leaving the eccentricity unchanged. This time is of the same order of magnitude as the viscous evolution time scale for a fully turbulent disk. Hence Iapetus need not be a captured satellite to account for its curious orbital signature.