Mimas and Pandora dance
Posted By Emily Lakdawalla
15-05-2013 17:02 CDT
I've been out of town for a couple of days and am overwhelmed with work and an overflowing email box. So what do I do about that? I ignore what I'm supposed to be doing and play with Cassini raw image data, of course. Here is a "mutual event" of Mimas (the bigger moon) and Pandora (the outer shepherd of the F ring).
The original set of images was centered on Mimas but when I animated it like that, it was hard to tell what the rings were doing. So instead I aligned the frames vertically on the edge of the A ring, which makes it clearer that you're seeing the rings "close up." Cassini's orbit is currently highly inclined (it's tilted more than 60 degrees). At the time that Cassini took these photos, it was near periapsis and plunging rapidly from north to south; it would cross the ring plane just 8 hours later. So even though Mimas appears to be moving vertically in the animation, it's not; you're actually seeing an effect of Cassini's vertical motion.
Watch Mimas closely and you'll see it's rotating, too. If you notice a falling donut at the bottom of the image, it's an artifact -- a mote of dust somewhere in the camera's optics.