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 ofimpact craters of about 20 km (12 mi) diameter are visible, but it is less cratered than nearbyPandora,Epimetheus, andJanus. From its very low density and relatively highalbedo, 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.
Prometheus is ashepherd satellite for the inner edge of Saturn's narrowF 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 theCassini 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 121:118mean-motion resonances withPandora.[11] The most appreciable changes in their orbits occur approximately every 6.2 years,[3] when theperiapsis of Pandora lines up with the apoapsis of Prometheus, as they approach to within approximately 1400 km. Prometheus is itself a significant perturber ofAtlas, with which it is in a 53:54 mean-longitude resonance.[3]
^Calculated from the standard gravitational parameterGM =(1.06602±0.00048)×10−2 km3·s–2 given by Lainey et al. (2023), divided by thegravitational 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.
