Updated Model of Saturn's Magnetic Field Based on All Available Data

Models of Saturn's magnetic field based on the initial orbits of the Cassini spacecraft [Dougherty et al, Science, 2005] revealed an axisymmetric magnetic field very much like that observed by the Pioneer and Voyager spacecraft decades earlier. Later a reference model based on the first fifteen orbits was derived that allowed for non-axial terms. These terms were small, but nonzero [Giamperi et al, 2006]. A distinct periodicity in the magnetic field at or close to the presumed rotation period of the planet was identified in the data as well, a signature inconsistent with an axisymmetric planetary field and inconsistent with a tilted dipole, the simplest model that would produce a periodic field. Since orbit insertion in July, 2004 Cassini has executed more than forty-five orbits in Saturn's magnetosphere and the magnetometer onboard has provided nearly continuous measurements during this time. With periapses at a variety of radial distances, latitudes, and planetary longitudes the global spatial coverage is now sufficient to reassess the planetary magnetic field. We use all available data obtained during the first three years of the Cassini prime mission and standard inversion techniques to derive an updated model of Saturn's planetary magnetic field.