Space Topics: Saturn
Epimetheus (S/1980 S3)
Janus' Co-Orbital Moon
Cassini captured this view on March 30, 2005, from a distance of only 74,600
kilometers. The view
is in enhanced color, comprised of three images captured through infrared,
green, and ultraviolet filters. Color variations in the image are most likely
a result of "photometric effects," changes in the reflectivity of the surface
of Epimetheus with the angle of the incoming sunlight. The large circular crater
in the lower center is Hilairea, which has a diameter of about 33 kilometers
(21 miles). To the lower left is the crater Pollux, with a reddish interior. Source
Credit: NASA / JPL / Space Science Institute |
Size: Irregular, 144 x 108 x 98 kilometers - 12th largest
moon of Saturn
Orbital radius: 151,522 kilometers - 2.51 Saturn radii
- between the F and G rings - co-orbital with Janus
Orbital period: 0.6942 days - about 1/23 of Titan’s
- 26 seconds faster than Janus
Discovery: 1966 by R. Walker; 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 Epimetheus
Voyager 1
Closest view was on November 12, 1980 at 22:48:34 UTC
Voyager 2
Closest view was on August 25, 1980 at 19:37:35 UTC
Cassini
March 29, 2005 at 23:25 UTC
"05EP" nontargeted flyby
Closest approach altitude 62,032 kilometers
Cassini
July 14, 2005 at 20:55 UTC
"11EP" nontargeted flyby
Closest approach altitude 76,782 kilometers
NASA / JPL / SSI / Ian Regan |
Cassini
December 3, 2007 at 06:58 UTC
"53EP" nontargeted flyby
Closest approach altitude 6,364 kilometers
Views of Epimetheus from Cassini and Voyager
Lumpy Epimetheus looks different with each spacecraft flyby. Four of the five images are from Cassini; the center image is from Voyager 1 (the black stripe across the moon is the shadow of the F ring). In the bottom row, colored dots show features that correlate between adjacent images.
Credit: NASA / JPL / SSI / Calvin Hamilton / Gordan Ugarkovic / Exploitcorporations
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