Like the scalpel in the hand of a skilled surgeon, Cassini radio signals have been dissecting Saturn’s rings since 2005. In a group of special Cassini orbits that place the main ring system between Cassini and the Earth (radio occultation orbits), perturbations in parameters of three nearly pure sinusoidal radio signals (0.94, 3.6, and 13 cm wavelength) simultaneously transmitted by Cassini through the rings are captured at one or more of the ground receiving stations of the NASA Deep Space Network (DSN). Each occultation is like an incision that slices the rings along a different track, unraveling detailed ring structure spanning almost all radial scales. The diffraction limit is overcome using coherency of the radio signals to reconstruct the observations much like the reconstruction of a giant hologram.
Collectively, the incisions provide global anatomy of many dynamical and other features with resolution as fine as few hundred meters and coarser, many are of known origin but others are of less understood cause. The latter include most of the remarkable structure of the optically thick Ring B, the widest and most massive main ring region, as well as other interesting tenuous features in Saturn’s Ring C. The radio anatomy extends down to the “cellular” level where information about the ring microstructure (particle size distribution, vertical profile, particle clustering in gravitational wakes, geometric wake parameters, …) is captured in the observed near-forward collective diffraction pattern, as well as in differential effects on the three radio signals.
Cassini continues to enrich unraveling this remarkable ring system during its extended missions performing more incisions that sample new observation geometries, some recently revealing surprising evidence for likely 800-year old collision of captured cometary material with inner Ring C.