Prometheus is extremely elongated, measuring approximately 137 km × 81 km × 56 km (85 mi × 50 mi × 35 mi). It has several ridges and valleys and a number of
impact craters of about 20 km (12 mi) diameter are visible, but it is less cratered than nearby
Pandora,
Epimetheus, and
Janus. From its very low density and relatively high
albedo, it is likely that Prometheus is a very porous icy body. There is much uncertainty in these values, however, and so this remains to be confirmed.
Interactions with F Ring and other moons
Prometheus is a
shepherd satellite for the inner edge of Saturn's narrow
F Ring.
Pandora orbits just outside the F Ring, and has traditionally been viewed as an outer shepherd of the ring; however, recent studies indicate that only Prometheus contributes to the confinement of the ring.[9][10]
Images from the
Cassini probe show that Prometheus's gravitational influence creates kinks and knots in the F Ring as it shepherds material from it. The orbit of Prometheus appears to be chaotic, due to a series of four 121:118
mean-motion resonances with
Pandora.[11] The most appreciable changes in their orbits occur approximately every 6.2 years,[3] when the
periapsis of Pandora lines up with the apoapsis of Prometheus, as they approach to within approximately 1400 km. Prometheus is itself a significant perturber of
Atlas, with which it is in a 53:54 mean-longitude resonance.[3]
Cassini image (with moon's Saturn-facing end at lower right) reveals a surface covered with a blanket of fine material.
Image from Jan. 27, 2010.
Saturnshine illuminates the moon's night side.
Brightened version of same image
Prometheus flyby (December 6, 2015)
Animations
Prometheus collides with the F ring, pulls a streamer, and leaves behind a dark channel. 12 seconds 107 kbit/s
Movie of Prometheus and the F Ring looped once. 5 seconds 48 kbit/s
Notes
^Calculated from the standard gravitational parameter GM = (1.06602±0.00048)×10−2 km3·s–2 given by Lainey et al. (2023), divided by the
gravitational constantG = 6.6743×10−2 km3·kg–1·s–2.[5]
^Cuzzi, J. N.; Whizin, A. D.; Hogan, R. C.; Dobrovolskis, A. R.; Dones, L.; Showalter, M. R.; Colwell, J. E.; Scargle, J. D. (April 2014). "Saturn's F Ring core: Calm in the midst of chaos". Icarus. 232: 157–175.
Bibcode:
2014Icar..232..157C.
doi:
10.1016/j.icarus.2013.12.027.
ISSN0019-1035.