Philip D. Nicholson (Cornell University), in collaboration with Richard G. French (Wellesley College) and Matthew M. Hedman (University of Idaho)
In earlier work (Hedman & Nicholson 2013, 2014, French et al. 2016) we used stellar and radio occultation data from the Cassini spacecraft to identify several density waves in Saturn’s C ring with resonances generated by internal f-mode oscillations within Saturn. The oscillations involved were sectoral modes (ie., modes with l = m) with m = 2, 3, 4 and 10, and were originally predicted by Marley & Porco (1993). An improved geometric solution for Cassini occultations, accurate to ~150 m, has led to the identification of an additional seven Saturn-driven waves in the inner C ring, four of which appear to be vertical waves with odd values of l-m (French et al. 2019). In addition, new phase-corrected wavelet techniques have revealed six more saturnian density waves in the middle C ring with m = 5, 6, 7, 8, 9 and 11 (Hedman et al. 2019). These advances provide a more complete picture of the spectrum of a giant planet’s normal modes and place constraints on Saturn’s internal structure and its rotation rate (Mankovich et al. 2019). Future work should identify higher-order modes but puzzles remain, including the distribution of wave amplitudes and the existence of multiple modes with m = 2 and 3.
