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Prometheus was discovered in 1980 from Voyager? photos. It is the inner shepherd satellite of the F ring. Prometheus has a number of ridges and valleys and several craters about 20 km in diameter but appears to be less cratered than the neighboring moons Pandora, Janus and Epimetheus. From its very low density and relatively high albedo, it seems likely that Prometheus is a very porous icy body. There is a lot of uncertainty in these values, however, and so this remains to be confirmed. The 1995/1996 Saturn Ring Plane Crossing observations found that Prometheus was lagging by 20 degrees from where it should have been based on Voyager 1981 data. This is much more than can be explained by observational error. It is possible that Prometheus's orbit was changed by a recent encounter with the F ring, or it may have a small companion moon sharing its orbit. *Orbital radius: 139,350 km *diameter: 91 km (145 x 85 x 62) *mass: 2.7×1017 kg *Orbital period: 0.6130 days *Orbital inclination: 0° |
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