A decade-long study tracking the intricate motions of Saturn’s ring moons shows that Pandora, located just outside the F Ring, actually is not gravitationally herding the narrow ring’s outer edge.
It, along with partner moon Prometheus, located just the inside the F-ring, actually stir up particles in the rings, but in the midst of the chaos, a stable core exists.
“The long-term stability of the narrow F Ring core has been hard to understand. Instead of acting as ‘shepherds,’ Prometheus and Pandora together stir the vast preponderance of the region into a chaotic state,” planetary scientist Jeffrey Cuzzi, with NASA’s Ames Research Center in Moffett Field, Calif., writes in a paper published in the April edition of Icarus.
Extrapolating from nearly 10 years worth of data collected by the Saturn-orbiting Cassini spacecraft, Cuzzi and colleagues ran computer simulations showing how complicated orbital dynamics can lead to what they call “calm in the midst of chaos.”
The explanation is quite nuanced, but basically has to do with the difference in timing between the ring particles’ motions and the moons’ orbits. The study showed a neat connection between Prometheus’ orbit and ring particles darting in and out which ends up keeping the ring in balance.
“Essentially, we find that the F Ring core is not confined by a combination of Prometheus and Pandora, but a combination of Prometheus and precession,” the authors write.
Precession is the change in orientation of a spinning body due to gravitational influences.