More Kronoseismology with Saturn's rings

Abstract

In a previous paper (Hedman and Nicholson 2013), we developed tools that allowed us to confirm that several of the waves in Saturn's rings were likely generated by resonances with fundamental sectoral normal modes inside Saturn itself. Here we use these same tools to examine eight additional waves that are probably generated by structures inside the planet. One of these waves appears to be generated by a resonance with a fundamental sectoral normal mode with azimuthal harmonic number m=10. If this attribution is correct, then the m=10 mode must have a larger amplitude than the modes with m=5-9, since the latter do not appear to generate strong waves. We also identify five waves with pattern speeds between 807 degrees/day and 834 degrees/day. Since these pattern speeds are close to the planet's rotation rate, they probably are due to persistent gravitational anomalies within the planet. These waves are all found in regions of enhanced optical depth known as plateaux, but surprisingly the surface mass densities they yield are comparable to the surface mass densities of the background C ring. Finally, one wave appears to be a one-armed spiral pattern whose rotation rate suggests it is generated by a resonance with a structure inside Saturn, but the nature of this perturbing structure remains unclear. Strangely, the resonant radius for this wave seems to be drifting inwards at an average rate of 0.8 km/year over the last thirty years, implying that the relevant planetary oscillation frequency has been steadily increasing.

arXiv comment45 Pages, 19 Figures, Accepted for publication in MNRAS

References in corpus (7)

• Dynamics of Saturn's great storm of 2010-2011 from Cassini ISS and RPWS
• Kronoseismology: Using density waves in Saturn's C ring to probe the planet's interior
• Origin of Tidal Dissipation in Jupiter: I. Properties of Inertial-Mode
• The long-term steady motion of Saturn's Hexagon and the stability of its enclosed jet-stream under seasonal changes
• Non-radial Oscillations in Rotating Giant Planets with Solid Cores: Application to Saturn and its Rings
• Unravelling Temporal Variability in Saturn's Spiral Density Waves: Results and Predictions
• Saturn Ring Seismology: Looking Beyond First Order Resonances

Cited by in corpus (19)

• Resonance locking as the source of rapid tidal migration in the Jupiter and Saturn moon systems
• Cassini Ring Seismology as a Probe of Saturn's Interior I: Rigid Rotation
• The B-ring's surface mass density from hidden density waves: Less than meets the eye?
• Ring dynamics around non-axisymmetric bodies with application to Chariklo and Haumea
• Kronoseismology IV. Six previously unidentified waves in Saturn's middle C ring
• How Janus' Orbital Swap Affects the Edge of Saturn's A Ring?
• What confines the rings of Saturn?
• Mapping spiral waves and other radial features in Saturn's rings
• Time-Series Analysis of Broadband Photometry of Neptune from K2
• Memoirs of a giant planet
• Kronoseismology V: A Panoply of Waves in Saturn's C Ring Driven by High-Order Internal Planetary Oscillations
• The dynamics of rings around Centaurs and Trans-Neptunian Objects
• Saturn's rings as a seismograph to probe Saturn's internal structure
• Axisymmetric density waves in Saturn's rings
• Occultation observations of Saturn's rings with Cassini VIMS
• Setting the Stage for Uranian Seismology from Rings and Radial Velocities
• Uranus' hidden narrow rings
• Excitation and Damping of Oscillation Modes in Gaseous Planets
• Constraining Saturn's interior with ring seismology: effects of differential rotation and stable stratification