A Decade of Cassini Radio Science so Far, and Three Spectacular Years Ahead

Over the past decade, the Cassini RSS (Radio Science Subsystem) instrument has provided fundamental new insights into many aspects of the Saturn system. Taking advantage of the capability to use up to three simultaneous wavelengths (Ka, X, and S bands), a series of occultation experiments of Titan and Saturn have provided detailed vertical profiles of the atmospheric and ionospheric structure, exhibiting seasonal and regional variability. Gravity experiments, conducted during close flybys of Saturn's moons, have yielded information about their internal structure, including evidence of sub-surface oceans on Titan and Enceladus. From dozens of ring occultation experiements, the radial structure, scattering properties, and particle sizes of the rings have been measured to high precision, enabling detailed comparative studies of ring dynamics and orbital characteristics. Recent bistatic observations of Titan, in which the transmitted signal reflects off of the specular point and is received on Earth, have traversed the northern polar regions, crossing the boundaries between seas and land, showing that the surface of the seas is remarkably smooth, and providing information about the dielectric properties of the liquids and surface materials. The best is yet to come, during the final three years of the Cassini mission, when the RSS instrument will observe the rings in a series of occultation measurements at their most favorable geometry of the entire Cassini mission, and a companion set of close fly-bys of Saturn will provide the first detailed determination of Saturn's gravitational field.