Orbits and masses of Saturn's coorbital and F-ring shepherding satellites

We have obtained numerically integrated orbits for Saturn's coorbital satellites, Janils and Epimetheus. together with Saturn's F-ring shepherding satellites, Prometheus and Pandora. The orbits are fit to astrometric observations acquired with the Hubble Space Telescope and from Earth-based observatories and to imaging data acquired from the Voyager spacecraft. The observations cover the 38 year period from the 1966 Saturn ring plane crossing to the spring of 2004. in the process of determining the orbits we have found masses for all four satellites. The ensities derived from the masses for Janus, Epimetheus, Prometheus. and Pandora in units of g cm(-3) are 0.61 (+0.07)(-0.06), 0.64(-0.09)(+0-13), 0.42(-0.13)(+0.27) and 0.54(-0.15)(+0.30), respectively. (C) 2004 Elsevier Inc. All riahts reserved.