Ephemerides of the Irregular Saturnian Satellites from Earth-based Astrometry and Cassini Imaging*

Abstract

Abstract We report a new determination of the orbits of the irregular Saturnian satellites. We fit their numerically integrated orbits to a data set containing Earth-based observations and imaging data from the Cassini spacecraft. We include the statistics of the observation residuals, the satellites’ orbital elements, and projected accuracies of the satellites’ positions. We also provide astrometric positions derived from the Cassini imaging. Two of the satellites are considered lost because they have not been observed for more than one epoch and have indeterminate uncertainties in their positions. Three of the satellites appear to be in a Kozai resonance, with one being the first irregular satellite of any planet found to be in a 270° rather than 90° resonance.