The history of Janus (http://en.wikipedia.org/wiki/Janus_%28moon%29) and Epimetheus's discovery is kind of interesting, since they were seen prior to space probes arriving at Saturn, but only just barely. In the sixties there were various observations of a satellite just outside the rings that was referred to as Janus, but the observations weren't entirely consistent with each other and not everyone saw it. In 1978, other astronomers figured out that there were actually two different objects.
Then in 1979, Pioneer 11 (which was mainly intended as a Jupiter probe) flew past Saturn in an encounter primarily designed to help planning for the subsequent Voyager flybys. By sheer coincidence, it nearly collided with either Janus or Epimetheus--I think that which one is actually unclear, because of the uncertainty in their precise orbits at that point, but the moon's shadow was observed by Pioneer 11's particle detectors.
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Date: 2008-01-12 04:15 pm (UTC)Then in 1979, Pioneer 11 (which was mainly intended as a Jupiter probe) flew past Saturn in an encounter primarily designed to help planning for the subsequent Voyager flybys. By sheer coincidence, it nearly collided with either Janus or Epimetheus--I think that which one is actually unclear, because of the uncertainty in their precise orbits at that point, but the moon's shadow was observed by Pioneer 11's particle detectors.