The behavior of spokes in Saturn’s B ring

Mitchell, C. J.; Porco, C. C.; Dones, H. L.; Spitale, J. N.

doi:10.1016/j.icarus.2013.02.011

Cited by 21 publications

(24 citation statements)

References 43 publications

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“…With regard to ring region phenomena, however, it has been reported that two types of disturbances in Saturn's rings exhibit periodicities which appear to be related to the PPOs. First, it has been found by Porco and Danielson (1982) and Mitchell et al (2013) that the occurrence of ring "spokes" appearing in the B ring near synchronous orbit is modulated at periods comparable with the PPO periods. Second, Hedman et al (2009) and Chancia et al (2019) have reported the presence of patterns in the tenuous material in Saturn's D ring and Roche division (between the A ring and the outer F ring) which rotate with periods near the concurrent dominant PPO period.…”

Section: Ppos and Mean Fields On Ring Region Field Linesmentioning

confidence: 99%

Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

et al. 2019

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We analyze periapsis pass magnetic field data from the final 23 orbits of the Cassini spacecraft at Saturn, uniquely encompassing auroral, subauroral, ring region, and intra-ring field lines, to determine the planetary period oscillations (PPOs) and mean residual fields in these regions. Dual modulation by northern and southern PPO systems is found almost continuously, demonstrating for the first time the presence of PPOs on and inside ring region field lines. The azimuthal component displays the largest 10-15nT PPO amplitudes on auroral field lines, falling across the subauroral region to~3-5 nT on main ring field lines in the northern hemisphere, less in the southern hemisphere, while increasing to~5-8 nT on D ring and intra-D ring field lines. Auroral and subauroral amplitudes mapped along field lines are in good agreement with previous analyses in regions of overlap. Colatitudinal and radial field oscillations generally have a half and a quarter the amplitude of the azimuthal component, respectively. Inner region oscillation phases are typically several tens of degrees "earlier" than those of outer subauroral and auroral regions. Mean residual poloidal fields (internal and ring current fields subtracted) show quasi-sinusoidal latitude variations of~2.5nT amplitude, with radial and colatitudinal fields approximately in quadrature. Mean azimuthal fields peaking at~15 nT are approximately symmetrical about the equator on and inside D ring field lines as previously reported, but are unexpectedly superposed on~3-5nT "lagging" fields which extend continuously through the ring region onto subauroral field lines north and south.

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Section: Ppos and Mean Fields On Ring Region Field Linesmentioning

confidence: 99%

Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

et al. 2019

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“…Indeed, there are several patterns in both the D ring and Roche Division which appear to be generated by resonances with multiple periodic perturbations with effective pattern speeds around 800 • /day and 820 • /day (Hedman et al 2009), and these may correspond to the 2:1 and 3:4 tesseral resonances, respectively. In addition, the dusty spokes that form close to the planetary co-rotation radius also exhibit periodicities that have been tied to Saturn's rotation rate (Porco & Danielson 1982;Porco 1983;Mitchell et al 2013). However, all of these previously-studied structures involve ring material composed primarily of micron-sized particles.…”

Section: Multiple M = +3 Waves In the Outer C Ringmentioning

confidence: 99%

More Kronoseismology with Saturn's rings

Hedman

Nicholson

2014

Monthly Notices of the Royal Astronomical Society

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In a previous paper (Hedman and Nicholson 2013), we developed tools which 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 • /day and 834 • /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.

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“…Energetic neutral atoms, generated by collisions between neutrals and charged particles, also display periodic behavior that can be observed on a global scale (Carbary, Mitchell, Brandt, Roelof, et al, ; Paranicas et al, ). Even spokes in Saturn's rings appear to show a periodic behavior (Mitchell et al, ; Porco & Danielson, ).…”

Section: Introductionmentioning

confidence: 99%

Energetic Electron Periodicities During the Cassini Grand Finale

et al. 2017

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The Cassini F ring and Proximal orbits took the spacecraft closer to Saturn than any previous mission and allowed determination of energetic charged particles (E > 20 keV) in the inner magnetosphere of the planet. The periodicities of the energetic electrons show a remarkable consistency when analyzed using Lomb periodograms. From the beginning of the F ring orbits in October 2016 to the end of the mission in September 2017, the particles manifest a strong main period of 10.79 h ± 0.01 h, with small Doppler‐related signals slightly above and below this period. The signal‐to‐noise ratio of the main period indicates one of the strongest periods ever seen in Saturn's magnetosphere. As implied by latitude separation, the main period seems to be associated with the northern hemisphere. The 10.79 h period is exactly the same as the single period observed during the early part of the Cassini mission in 2005–6 when Saturn experienced southern summer. A simple rotating searchlight model can simulate the periodograms.

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The behavior of spokes in Saturn’s B ring

Cited by 21 publications

References 43 publications

Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

Magnetic Field Observations on Cassini's Proximal Periapsis Passes: Planetary Period Oscillations and Mean Residual Fields

More Kronoseismology with Saturn's rings

Energetic Electron Periodicities During the Cassini Grand Finale

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