Saturn is the sixth planet from the Sun and is the second largest in the solar system with an equatorial diameter of 119,300 kilometers (74,130 miles). Much of what is known about the planet is due to the Voyager explorations in 1980-81. Saturn is visibly flattened at the poles, a result of the very fast rotation of the planet on its axis. Its day is 10 hours, 39 minutes long, and it takes 29.5 Earth years to rotate about the Sun. The atmosphere is primarily composed of hydrogen with small amounts of helium and methane. Saturn is the only planet less dense than water (about 30 percent less). In the unlikely event that a large enough ocean could be found, Saturn would float in it. Saturn's hazy yellow hue is marked by broad atmospheric banding similar to, but fainter than, that found on Jupiter.
The wind blows at high speeds on Saturn. Near the equator, it reaches velocites of 500 meters a second (1,100 miles an hour). The wind blows mostly in an easterly direction. The strongest winds are found near the equator and velocity falls off uniformly at higher latitudes. At latitudes greater than 35 degrees, winds alternate east and west as latitude increases.
Saturn's ring system makes the planet one of the most beautiful objects in the solar system. The rings are split into a number of different parts, which include the bright A and B rings and a fainter C ring. The ring system has various gaps. The most notable gap is the Cassini [kah-SEE-nee] Division, which separates the A and B rings. Giovanni Cassini discovered this division in 1675. The Encke [EN-kee] Division, which splits the A Ring, is named after Johann Encke, who discovered it in 1837. Space probes have shown that the main rings are really made up of a large number of narrow ringlets. The origin of the rings is obscure. It is thought that the rings may have been formed from larger moons that were shattered by impacts of comets and meteoroids. The ring composition is not known for certain, but the rings do show a significant amount of water. They may be composed of icebergs and/or snowballs from a few centimeters to a few meters in size. Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby satellites. This phenomenon is demonstrated by the relationship between the F-ring and two small moons that shepherd the ring material.
Radial, spoke-like features in the broad B-ring were also found by the Voyagers. The features are believed to be composed of fine, dust-size particles. The spokes were observed to form and dissipate in the time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.
Saturn has 18 confirmed moons, the largest number of satellites of any planet in the solar system. In 1995, scientists using the Hubble Space Telescope sighted four objects which might be new moons.
Mass (kg) ......................................... 5.688e+26
Mass (Earth = 1) ................................. 9.5181e+01
Equatorial radius (km) ............................... 60,268
Equatorial radius (Earth = 1) .................... 9.4494e+00
Mean density (gm/cm^3) ................................. 0.69
Mean distance from the Sun (km) ............... 1,429,400,000
Mean distance from the Sun (Earth = 1) ............... 9.5388
Rotational period (hours) ............................ 10.233
Orbital period (years) ............................... 29.458
Mean orbital velocity (km/sec) ......................... 9.67
Orbital eccentricity ................................. 0.0560
Tilt of axis .......................................... 25.33°
Orbital inclination ................................... 2.488°
Equatorial surface gravity (m/sec^2) ................... 9.05
Equatorial escape velocity (km/sec) ................... 35.49
Visual geometric albedo ................................ 0.47
Magnitude (Vo) ......................................... 0.67
Mean cloud temperature ............................... -125°C
Atmospheric pressure (bars) ............................. 1.4
Atmospheric composition
Hydrogen ............................................ 97%
Helium ............................................... 3%
The following is a summary of the rings of Saturn.
Name Distance* Width Thickness Mass Albedo -------------------------------------------------------------------- D 67,000 km 7,500 km ? ? ? C 74,500 km 17,500 km ? 1.1x10^18 kg 0.25 Maxwell Gap 87,500 km 270 km B 92,000 km 25,500 km 0.1-1 km 2.8x10^19 kg 0.65 Cassini Div 117,500 km 4,700 km ? 5.7x10^17 kg 0.30 A 122,200 km 14,600 km 0.1-1 km 6.2x10^18 kg 0.60 Encke gap 133,570 km 325 km Keeler gap 136,530 km 35 km F 140,210 km 30-500 km ? ? ? G 165,800 km 8,000 km 100-1000 km 6-23x10^6 kg ? E 180,000 km 300,000 km 1,000 km ? ?
*The distance is measured from the planet center to the start of the ring.
Saturn has 18 officially recognized and named satellites. In addition, there are other unconfirmed satellites. One circles in the orbit of Dione, a second is located between the orbits of Tethys and Dione, and a third is located between Dione and Rhea. The unconfirmed satellites were found in Voyager photographs, but were not confirmed by more than one sighting. Recently, the Hubble Space Telescope imaged four objects that might be new moons.
Several generalizations can be made about the satellites of Saturn. Only Titan has an appreciable atmosphere. Most of the satellites have a synchronous rotation. The exceptions are Hyperion, which has a chaotic orbit, and Phoebe. Saturn has a regular system of satellites. That is, the satellites have nearly circular orbits and lie in the equatorial plane. The two exceptions are Iapetus and Phoebe. All of the satellites have a density of < 2 gm/cm3. This indicates they are composed of 30 to 40% rock and 60 to 70% water ice. Most of the satellites reflect 60 to 90% of the light that strikes them. The outer four satellites reflect less than this and Phoebe reflects only 2% of the light that strikes it.
The following table summarizes the radius, mass, distance from the planet center, discoverer and the date of discovery of each of the confirmed satellites of Saturn:
Radius Mass Distance Moon # (km) (kg) (km) Discoverer Date -------------------------------------------------------------------------- Pan XVIII 9.655 ? 133,583 M. Showalter 1990 Atlas XV 20x15 ? 137,640 R. Terrile 1980 Prometheus XVI 72.5x42.5x32.5 2.7e+17 139,350 S. Collins 1980 Pandora XVII 57x42x31 2.2e+17 141,700 S. Collins 1980 Epimetheus XI 72x54x49 5.6e+17 151,422 R. Walker 1966 Janus X 98x96x75 2.01e+18 151,472 A. Dollfus 1966 Mimas I 196 3.80e+19 185,520 W. Herschel 1789 Enceladus II 250 8.40e+19 238,020 W. Herschel 1789 Tethys III 530 7.55e+20 294,660 G. Cassini 1684 Telesto XIII 17x14x13 ? 294,660 B. Smith 1980 Calypso XIV 17x11x11 ? 294,660 B. Smith 1980 Dione IV 560 1.05e+21 377,400 G. Cassini 1684 Helene XII 18x16x15 ? 377,400 Laques-Lecacheux 1980 Rhea V 765 2.49e+21 527,040 G. Cassini 1672 Titan VI 2,575 1.35e+23 1,221,850 C. Huygens 1655 Hyperion VII 205x130x110 1.77e+19 1,481,000 W. Bond 1848 Iapetus VIII 730 1.88e+21 3,561,300 G. Cassini 1671 Phoebe IX 110 4.0e+18 12,952,000 W. Pickering 1898 Possible New Satellites of Saturn
