Abstract
We identify multiple periodic dusty structures in Saturn's Roche Division, a faint region spanning the ∼ 3000 km between the A and F rings. The locations and extent of these features vary over Cassini's tour of the Saturn system, being visible in 2006 and 2016–2017, but not in 2012–2014. These changes can be correlated with variations in Saturn's magnetospheric periods. In 2006 and 2016–2017, one of the drifting magnetospheric periods would produce a 3:4 resonance within the Roche Division, but in 2012–2014 these resonances would move into the A ring as the magnetospheric periods converged. A simple model of magnetic perturbations indicates that the magnetic field oscillations responsible for these structures have amplitudes of a few nanotesla, comparable to the magnetic field oscillation amplitudes of planetary period oscillations measured by the magnetometer onboard Cassini. However, some previously unnoticed features at higher radii have expected pattern speeds that are much slower than the magnetospheric periodicities. These structures may reflect an unexpectedly long-range propagation of resonant perturbations within dusty rings.
Highlights
The Roche Division is a sparsely populated region of Saturn’s rings located between the outer edge of the A ring and the F ring. Burns et al (1983) first noted the presence of tenuous ring material between the A and F rings in a high phase angle Voyager 2 image of the region
We present the theoretical background of Lindblad resonances in planetary rings in Section 2, with particular emphasis on their framework in dusty rings, and our model of electromagnetic perturbations
We can characterize the Roche Division patterns using the radius of the peak amplitude and the equivalent pattern speed given by Equation 4, along with the structure’s peak amplitude and width
Summary
The Roche Division is a sparsely populated region of Saturn’s rings located between the outer edge of the A ring and the F ring. Burns et al (1983) first noted the presence of tenuous ring material between the A and F rings in a high phase angle Voyager 2 image of the region. The Roche Division is a sparsely populated region of Saturn’s rings located between the outer edge of the A ring and the F ring. It was referred to as the Pioneer Division, following Pioneer 11 ’s discovery of the F ring (Gehrels et al 1980). The image shows several diffuse bands of dust populating almost the entire Roche Division. The Roche Division is home to two of Saturn’s innermost moons, Atlas and Prometheus, which stir up and provide a source of dust in their vicinity. The outermost dust band, at approximately 139, 400 km from Saturn’s center, is typically the brightest feature in the region. The outermost dust band, at approximately 139, 400 km from Saturn’s center, is typically the brightest feature in the region. Hedman and Carter (2017) showed that this ringlet is in a co-orbital 1:1 resonance with Prometheus, but strangely precesses
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