Prometheus, Pandora, and the braided F ring in motion
Posted By Emily Lakdawalla
23-03-2015 17:19 CDT
On a day when my to-do list is long and overwhelming, I often find myself ignoring the list and turning to the Cassini raw images website. Especially when I know that Cassini has been doing something cool recently, like taking a long, high-resolution movie of the F ring. The F ring is a thin, dusty one with a complex shape that's constantly being disturbed and deranged by the encroachment of Prometheus. Sometimes Prometheus' slightly eccentric orbit takes it right into the F ring and back out again, whereupon it pulls out streamers of material, leaving dark lanes next to the streamers. Prometheus and its streamers orbit Saturn just slightly faster than the stuff located farther from Saturn in the F ring, so the dark lanes stretch out and out and out until they wrap right around Saturn, making alternating light-and-dark spirals. Meanwhile, knots of material in the F ring form and are torn apart again over the course of months. Pandora orbits outside it all, having little effect on the shape of the F ring despite its proximity to it.
Here are stills of Prometheus and Pandora with the ring. The phase angle is very high here, so both moonlets and the ring are lit very nearly from behind; the moons appear as very thin crescents, sunlit from the lower right. Each moon is more illuminated by Saturnshine, striking them from the left. In the Prometheus one you can actually see the dark lanes in the inner F ring crossing over at least two other ring waves that have coiled tightly around Saturn by Keplerian shear. I wish I could live on a space station levitating above the rings to watch these dynamics in their natural slow motion!