Kronoseismology: Probing Saturn’s Interior Via Its Rings
When
Where
Dr. Philip Nicholson
Professor
Cornell University
In previous work (Hedman & Nicholson [2013] Astron. J. 146, 12; Ibid [2014] MNRAS 444, 1369) we used stellar occultation data acquired by the VIMS instrument on the Cassini spacecraft to identify several inward-propagating density waves in Saturn's C ring with outer Lindblad resonances (OLRs) generated by internal oscillations in Saturn. The oscillations involved are sectoral f-modes (ie., fundamental modes with l = m), as originally discussed by Marley & Porco [1993]. In addition, five outward-propagating waves between radii of 84,800 and 86,600 km have been identified as density waves driven by 3:2 tesseral resonances with fixed gravitational anomalies within the planet. We have now examined six additional waves from the catalog of Baillie et al. [2011], which are both weaker and shorter in wavelength than the previously-identified waves. We use a modified version of our previous wavelet-based technique to coadd phase-corrected spectra from multiple occultations, using trial values of `m' and the pattern speed to predict the relative phases of the waves. This enables us to detect waves too weak to see in individual data sets. Two of the new waves appear to be due to additional saturnian f-modes, but the other four waves appear to be in a new class: outward-propagating bending waves driven at outer vertical resonances (OVRs) with asymmetric Saturn internal oscillations for which l = m + 1. All of the newly-identified waves are in the inner C ring, at radii less than 77,000 km. These waves, once they are securely identified, offer the possibility of refining models of Saturn's interior structure.