Before
the first Voyager encounter, astronomers believed Saturn
had 11 satellites. Now they know it has at least 17 and
possibly more. Three of the 17 were discovered by Voyager
1. Three additional possible satellites have been identified
in imaging data since the Voyager 2 encounter. (Three others
were discovered in ground-based observations.)
The
innermost satellite, Atlas, orbits near the outer edge of
the A-ring and is about 40 by 20 kilometers (25 by 15 miles)
in size. It was discovered in Voyager 1 images.
The
next satellite outward, Prometheus, shepherds the inner
edge of the F-ring and is about 140 by 100 by 80 kilometers
(90 by 60 by 50 miles). Next is Pandora, outer shepherd
of the F-ring, 110 by 90 by 80 kilometers (70 by 55 by 50
miles). Both shepherds were found by Voyager 1.
Next
are Epimetheus and Janus, which share about the same orbit
-- 91,000 kilometers (56,600 miles) above the clouds. As
they near each other, the satellites trade orbits (the outer
is about 50 kilometers, or 30 miles, farther from Saturn
than the inner). Janus is 220 by 200 by 160 kilometers (140
by 125 by 100 miles), and Epimetheus is 140 by 120 by 100
kilometers (90 by 70 by 50 miles). Both were discovered
by ground-based observers.
One
new satellite, Helene, shares the orbit of Dione, about
60 degrees ahead of its larger companion, and is called
the Dione Trojan. It is about 36 by 32 by 30 kilometers
(22 by 20 by 19 miles). Helene was discovered in ground-based
photographs.
Two
more satellites are called the Tethys Trojans because they
circle Saturn in the same orbit as Tethys, about 60 degrees
ahead of and behind that body. They are Telesto (the leading
Trojan) and Calypso (the trailing Trojan). Both were found
in 1981 among ground-based observations made in 1980. Telesto
is 34 by 28 by 26 kilometers (21 by 17 by 16 miles) and
Calypso is 34 by 22 by 22 kilometers (21 by 14 by 14 miles).
There
are three unconfirmed satellites. One circles Saturn in
the orbit of Dione, a second is located between the orbits
of Tethys and Dione, and the third, between Dione and Rhea.
All three were found in Voyager photographs, but were not
confirmed by more than one sighting.
