Saturn

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Vital Statistics

• Average distance from Sun: 886 million miles
• Perihelion: 839 million; Aphelion: 933 million
• Takes 29.46 years to orbit the Sun
• Diameter 74,600 miles. Even more flattened at the poles than Jupiter.
• Also more gaseous and rarified than Jupiter.
• Average density 0.7 - actually less dense than water.
• Rotates in 10 1/4 hours. 95 times the Earth's mass.
• Chemically about the same as Jupiter. Has a magnetic field, but weaker than Jupiter's.

As Seen From Earth

• Saturn averages about Magnitude 0 and looks yellowish
• Every 14 years Saturn shows its rings edge-on to Earth and Earth passes through the ring plane. The rings are so thin they disappear to even the largest telescopes at the exact time of ring-plane crossing.

Saturn's Rings

Makeup of the Rings

• Outer diameter of the A Ring is about 171,000 miles. The rings are at most a few km thick and some people think they may only be meters thick.
• The particles making up the rings are much coarser than Jupiter's rings -- mm. size and larger.
• The C Ring is very "thin," the A and B rings "thicker" (less transparent). Tenuous rings extend between Saturn and the C ring and out from the A ring. Several narrow rings occur just outside the A ring.
• Cassini's Division is not entirely void but contains fine material similar to Jupiter's ring.
• Gaps occur in the rings due to Saturn's satellites. Particles moving within Cassini's Division would orbit Saturn in periods ranging from 11 hr. 19 min. to 12 hr. 5 min. This is 1/2 the period of the satellite Mimas, 1/3 that of Enceladus, 1/4 that of Tethys and 1/9 that of Rhea. This is another example of Resonance. Smaller gaps have been noted in the rings and are due to other resonances.

The Moons of Saturn

Saturn has 52 known satellites as of 2008, 7 of which were discovered by the Voyager spacecraft.The largest and most interesting is Titan, which is 3600 miles in diameter and 922,000 miles from Saturn. It is the only satellite to have a thick atmosphere, and a surprisingly dense one, too: 1.6 atmospheres.

In Greek mythology, Saturn fathered the Titans as well as Jupiter (who became ruler of Olympus after defeating the Titans). So Saturn's moons were named after Titans and their descendants. More recently the naming has been extended to giants from other cultures' mythologies.

Pan

• 20 km diameter
• 133,583 km distance
• Unique in the Solar System so far: orbits within Saturn's A ring and helps to define a narrow gap in the rings called the Encke Division.
• There may be many other such moonlets within the rings, helping to define gaps and ringlets. They don't have to be very big; a few hundred meters will do nicely.

Atlas (A Ring Shepherd)

• 137,200 km from Saturn (77,000 km above cloud tops).
• Just outside the A ring and probably responsible for maintaining its sharp edge.
• Measures about 20 x 40 km.
• Period 14.4 hours.

Prometheus (Inner F-ring Shepherd)

• 80 x 140 km
• 139,300 km from Saturn.

Pandora (Outer F-ring Shepherd)

• 70 x 110 km
• 141,650 km from Saturn.
• These two moons probably keep the narrow F-ring in place.
• Periods 14.7 and 15.1 hours.

Janus and Epimetheus (Co-orbital moons)

• 100 x 140 and 160 x 220 km.
• Share almost (but not exactly) identical orbits 151,400 km from Saturn. (The orbits are about 60 km apart.)
• Every few years one overtakes the other. Possibly they alternate as leader and follower, exchanging orbits during encounters.
• May be fragments of a moon shattered by impact.

Mimas

• 390 km in diameter
• 186,000 km from Saturn
• Nicknamed the "Death Star" by Voyager scientists because a huge crater 130 km in diameter with a central peak 9 km high made it resemble the "Death Star" from Star Wars. The impact must have nearly split Mimas.
• Features on Mimas are named for figures from the Legend of King Arthur.
• Period 23 hours.

Enceladus

• 500 km in diameter
• 238,000 km from Saturn
• Very reflective and bright, with a geologically young surface that has obliterated many craters. Large areas have grooved terrain rather like Jupiter's moon Ganymede.
• Period 33 hours.

Tethys

• 1060 km in diameter
• 294,700 km from Saturn.
• Icy and heavily cratered. Has one huge crater (Odysseus) 400 km in diameter, but very shallow due to plastic flow of its icy crust.
• Opposite (and probably related) is a huge rift that extends 3/4 of the way around the satellite.
• Features on Tethys are named from the Odyssey and Iliad.
• Period 45 hours.

Telesto and Calypso (Tethys Lagramgian moons)

• 26 x 34 and 22 x 34 km.
• In same orbit as Tethys, but one leads Tethys by 60 degrees and one trails by 60 degrees

Dione

• 1120 km in diameter,
• 377,400 km from Saturn.
• Bright, icy, and cratered. Has a dark trailing hemisphere with bright wispy streaks (produced by water vented from within?).
• Features on Dione are named from the Aeneid.
• Period 66 hours.

Helene (Dione Lagrangian moon)

• 30 x 36 km.
• In Dione's orbit, leads it by 60 degrees.

Rhea

• 1530 km in diameter
• 527,100 km from Saturn.
• Very similar in most respects to Dione.
• Period 4.5 days.

Titan

• 5150 km in diameter,
• 1,222,000 km from Saturn.
• Loses a close contest with Jupiter's Ganymede as largest moon in the Solar System.
• Has a reddish, nitrogen atmosphere, 1.6 times the Earth's atmospheric pressure.
• Only Satellite with a dense atmosphere.
• Period 16 days.

Hyperion

• 220 x 410 km. Has been likened to a hamburger or hockey puck in shape.
• 1,481,000 km from Saturn
• Period 21.3 days.
• Its irregular shape results in complex gravitational interactions with other satellites and a chaotic rotation.

Iapetus

• 1460 km in diameter,
• 3,561,000 km from Saturn.
• Remarkable for having one bright hemisphere and one very dark. The dark, leading hemisphere may be coated by dark carbonaceous debris swept up by the satellite.
• Period 79 days.

Phoebe

• 220 km in diameter
• 12,954,000 km from Saturn.
• A dark round moon, possibly a captured rocky asteroid.
• Retrograde orbit.
• Period 406 days.

Dance of the Moons

If Jupiter was created by a special-effects artist, Saturn was designed by achoreographer. Nowhere else do we find such an intricate set of orbital relationshipsamong moons. There are shepherd moons, gaps in the rings created by resonances withsatellites, co-orbital moons and Moons in Trojan configuration.

For more information on interactions between moons and rings, see Rings and Resonances

References

• James B. Pollack and Jeffrey N. Cuzzi, 1981, Rings in the Solar System. Scientific American, vol.245, no. 5, pp. 104-129
• Torrance V. Johnson and Laurence A. Soderblom, 1982, The moons of Saturn. Scientific American, vol. 246, no. 1, pp. 100-117
• Tobias Owen, 1982, Titan. Scientific American, vol. 246, no. 2, pp. 98-109

Pioneer 11 Saturn Encounter.

Special issue of Science, vol. 207, No. 4429, January 25, 1980.

Voyager 1 Saturn Encounter.

Special issue of Science, vol. 212, No. 4491, April 10, 1981.

Voyager 2 Saturn Encounter.

Special issue of Science, vol. 215, No. 4532, January 29, 1982.

NASA Publications:

• NASA Special Publication SP-420, 1977 Voyager to Jupiter and Saturn
• NASA Special Publication SP-446, 1980, Pioneer: First to Jupiter, Saturn, and beyond
• NASA Special Publication SP-451, 1982 Voyages to Saturn
• NASA Publication JPL-400-100, 1980 Voyager 1 encounters Saturn

Return to Planetary Images Index
Access Course Notes on Planetary Geology
Access Astronomy Notes Index
Return to Professor Dutch's Home Page

Created 20 May 1997, Last Update 11 January 2020