Space Topics: Saturn
Janus (S/1980 S1)
Epimetheus' Co-Orbital Moon
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Voyager 2 captured this view of Janus on August 25, 1981
at 21:07 UTC. Credit: NASA / JPL
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Size: Irregular, 196 x 192 x 150 kilometers
- 10th largest moon of Saturn
Orbital radius: 151,452 kilometers - 2.51 Saturn radii - between
the F and G rings - co-orbital with Epimetheus
Orbital period: 0.6945 days - about 1/23 of Titan’s
- 26 seconds slower than Epimetheus
Discovery: 1966 by Andouin Dollfus; Stephen Larson and John
Fountain showed in 1977 that Epimetheus and Janus were distinct.
Epimetheus and Janus share almost the same orbit (within 50 kilometers
or 30 miles of each other) within the large gap between Saturn's F and
G rings. At any given time, one or the other is closer to Saturn
and is consequently orbiting slightly faster. When the inner of the
two catches up to the outer, a complicated
gravitational dance causes Janus and Epimetheus to exchange places. At
present, Epimetheus is the farther of the two from Saturn.
Flybys of Janus
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NASA / JPL / Emily Lakdawalla |
Voyager 1
Closest view was on November 12, 1980 at 22:22:58 UTC
Voyager 2
Closest view was on August 25, 1980 at 21:07:11 UTC
Future Flybys
Cassini
Several flybys are planned. The first will be on April 29, 2006 (rev
23). The closest flyby will be on June 30, 2008 (rev 74) at about 44,636
kilometers (26,782 miles).
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