Unveiling What Makes Saturn Ring: Quantifying the Amplitudes of Saturn's Planetary Normal-Mode Oscillations and Trends in C-Ring Properties Using Kronoseismology (VII)

TL;DR

This study analyzes Saturn's ring wave amplitudes to infer internal planetary oscillations and ring properties, revealing complex mode excitation mechanisms and regional variations in ring particle density and viscosity.

Contribution

It introduces a detailed analysis of Saturn's normal-mode oscillations and ring properties using high-resolution occultation data, expanding understanding beyond rotation rates to include amplitude and excitation factors.

Findings

Ring particle density varies with distance from Saturn.

Ring viscosity is lower in the outer C-ring, indicating high porosity.

Saturn's normal modes are influenced by both deep and shallow sources.

Abstract

Certain spiral density waves in Saturn's rings are generated through resonances with planetary normal modes, making them valuable probes of Saturn's internal structure. Previous research has primarily focused on the rotation rates of these waves. However, other characteristics of these waves also contain valuable information about the planet's interior. In this work, we investigate the amplitudes of the waves across the C-ring by analyzing high signal-to-noise profiles derived from phase-corrected averages of occultation profiles obtained by Cassini's Visual and Infrared Mapping Spectrometer (VIMS). By fitting these wave profiles to linear density wave models, we estimate the ring's surface mass density, mass extinction coefficient and effective kinematic viscosity at 34 locations in the C-ring, as well as the amplitude of the gravitational potential perturbations associated with 6 satellite resonances and 28 planetary normal mode resonances. Our estimates of the C-ring's mass extinction coefficient, indicate that the typical particle mass density is around 0.3 g/cm^3 interior to 84,000 km, but can get as low as 0.03 g/cm^3 exterior to 84,000 km. We also find the ring's viscosity is reduced in the outer C-ring, which is consistent with the exceptionally high porosity of the particles in this region. Meanwhile, we find the amplitudes of Saturn's normal modes are complex functions of frequency, l and m, implying that multiple factors influence how efficiently these modes are excited. This analysis identified two primary sources of these normal-mode oscillations: a deep source located close to Saturn's core, and a shallow source residing near the surface.