A New Pattern in Saturn’s D Ring

Abstract:

The D ring is Saturn’s innermost ring, and it is amongst the most time-variable components of Saturn’s ring system. A dramatic new example of this dynamism was found in images obtained in 2012-2014 by the cameras onboard the Cassini spacecraft. These data reveal periodic brightness variations extending across a 2000-km-wide swath of the inner D ring that was largely featureless prior to 2011. Furthermore, the radial wavelength of this pattern decreased by over a factor of four in eighteen months. Similarly periodic patterns with steadily decreasing wavelengths were previously observed in other parts of Saturn's and Jupiter's rings, and each of those structures appears to have been generated by some event that produced organized non-circular motions in the ring-particles' orbits. This new pattern seems to represent another example of this sort of structure. However, this new pattern is special because the ring-disturbing event required to produce the observed ring features must have occurred in late 2011, while the Cassini spacecraft was in orbit around Saturn. Images obtained before and after the event, as well as data from other instruments, could therefore help clarify the origin and nature of this disturbance.