Hedman, M.M., Burns, J.A., Tiscareno, M.S., Nicholson, P.D., Porco, C.C. (2007). "Possible Resonances with Saturn's Rotation in the Rings." Eos Trans. AGU 88(52) Fall Meet. Suppl., Abstract P31A-0189.
Images from the Cassini spacecraft reveal several unexpected structures in Saturn's faint rings that could be caused by irregularities in the planet's interior and/or magnetosphere. |
Images of the D ring from 2006 and early 2007 show structures between 71,000 and 73,000 km from Saturn's center that each have mode-2 rotational symmetry around the planet (i.e. the brightness variations with radius are the same
on opposite sides of the planet). Similarly, images of the region between the A and F rings taken in late 2006 contain azimuthally periodic patterns around 137,500 km. These sorts of periodic structures are probably generated at resonances, where the orbital period of the particles in the ring is
close to a whole number ratio times the period of some perturbing force. Indeed, similar brightness variations are found in the G ring near the 8:7 Inner Lindblad Resonance with Mimas.
The locations and symmetry properties of the observed patterns, along with the speed with which they circle Saturn, can be used to identify not only the types of resonances that produce and sustain these features, but also
the frequencies of the perturbing forces. Patterns in the D ring are consistent with 2:1 Inner Lindblad resonances, while those outside the A ring appear to be caused by 3:4 Outer Lindblad Resonances. In both locations, multiple perturbing forces with periods ranging between 10.5 and
10.9 hours appear to be affecting the ring material. As this overlaps the span of periods associated with Saturn's winds and magnetosphere, the observed ring structures may be created by anomalies in Saturn's gravitational and/or magnetic field. The relative strength and persistence
of these patterns may therefore provide information about the the structure of the planet's interior or the dynamics of the inner magnetosphere.