SATURN (MYTHOLOGY) An ancient Roman god of agriculture, Saturn was later identified with the Greek god CRONUS, who fled to Italy after his dethronement by Zeus as ruler of the universe. Saturn settled on Rome's CAPITOLINE HILL and taught the people agriculture and other arts of civilization. He helped usher in a period of prosperity that became known as the Golden Age. One day Saturn vanished from the earth. At the Saturnalia festival, held in his memory every December (the winter sowing season), masters and slaves shared the same table as a sign that no social divisions existed during the Golden Age. Saturn also gave his name to a planet and to Saturday.
Saturn Divorcee wearing 7 rings from 7 failed marriages conceiving 18 children yet still cosmetically adorned in wait for whichever husband may happen to return daring the bachelor to come along and experience this bride and her pregnancies before her insatiable loneliness with its responsibilities forces him to move on. carlyle miller
SATURN (PLANET) Even when viewed through a small telescope, Saturn and its ring system is one of the most unique objects in the sky. With a large modern telescope in good observing conditions, the planet appears as a light yellow and gray banded oblate spheroid. Like the other giant planets--Jupiter, Uranus, and Neptune--the visible planet is the cloud top of an extensive gaseous atmosphere. THE PLANET Saturn orbits the Sun at a mean distance of 1.427 billion km (0.893 billion mi) with a period of 29.4577 tropical years. The orbit is inclined 2.49 degrees to the ecliptic, or Earth-orbital, plane and has an eccentricity of 0.0556. At Saturn's distance from the Sun, it receives only 0.01 of the unit solar radiation flux that the Earth does. Among planets in the SOLAR SYSTEM, Saturn is second in size only to Jupiter; Saturn has an equatorial diameter of 120,660 km (74,980 mi). Its volume would enclose about 769 Earth-sized bodies. Saturn's internal rotation period, defined by periodic radio emissions, is 10.657 hours. This fast rotation is responsible for Saturn's equatorial bulge and oblate shape. The equatorial-polar-diameter ratio is 1.12 to 1. Saturn's mass is 5.686 X 10 to the power of 26 kg (12.54 X 10 to the power of 26 lb), or 95.147 times the Earth's. Thus the average density is only 0.69 g/cu cm (43 lb/cu ft), which is much less than water, indicating a very deep atmosphere and a very small core. Atmosphere Saturn is one of the giant outer planets, which are characterized by their large size, low density, and corresponding extensive atmospheres. Current models of the interior indicate that below the relatively thin opaque cloud layer is an extensive, clear hydrogen-helium atmosphere. Data on the internal heat flux, the detailed gravity field, and the observed upper-atmosphere hydrogen-helium ratio satisfy a model of the interior where the ratio of hydrogen to helium decreases with depth. The gas density gradually increases downward and the gas transforms into a liquid. Further down the pressures increase to a critical level, and there the hydrogen becomes metallic. A small core of silicate material probably exists at the center. The Saturnian atmosphere is characterized by counterflowing easterly and westerly jet streams that, at the equator, reach a speed of 480 m/sec (1,070 mph) relative to the clouds at 40 degrees latitude. The zonal jets do not change appreciably with time, but smaller-scale spots, waves, and eddies were seen on VOYAGER spacecraft images to change a time scale of hours. Such smaller features are usually hard to observe on Saturn because of an obscuring haze layer above the planet's cloud surface. One northern hemisphere feature, however, known as the Great White Spot, does become significantly noticeable for Earth-based viewers about every 29 years. The spot is apparently an upwelling of ammonia-rich materials; the ammonia then crystallizes at this greater height to produce the white color. The spot sometimes expands until it becomes a band of clouds girdling the planet. Traces of methane, ethane, phosphine, and acetylene also exist in the hydrogen-helium atmosphere. Various colors that have been observed probably result from chromophores being produced by the interaction of such trace elements as sulfur or carbon compounds with ionospheric charged particles and lightning. This condition of chemical nonequilibrium is produced by vertical mixing, driven by heat from the gravitational energy released by the precipitation of liquid helium. Saturn radiates 2 to 3 times the heat absorbed from the Sun. Magnetic Field Saturn has a strong, dipolar magnetic field tilted only 0.7 degrees from the rotational axis. The subsolar magnetopause is 6.38 million km (3.96 million mi) from Saturn on the average. A magnetic tail extends in the direction away from the Sun much like cometary plasma tails. Saturn's magnetic field traps charged particles coming from the solar wind. These particles move along magnetic-field lines but are absorbed by satellites and ring particles. The charged particles that impinge on the ionosphere create airglow emissions. Origin and Evolution Saturn is far enough away from the Sun to retain the light elements (hydrogen and helium) and therefore has solarlike chemical abundance. Saturn's mass, unlike that of the Sun, was not large enough to initiate the fusion process, and Saturn, unlike Jupiter, did not give off enough excessive heat to drive out water from the inner satellites. THE RINGS Saturn's white rings were first seen by Galileo Galilei in 1610; his small, imperfect telescope showed the planetary disk flanked by what he first interpreted as being two smaller bodies. Christiaan HUYGENS correctly theorized (late 1650s) the ring nature of these alleged "companions." James Clerk MAXWELL mathematically demonstrated (1857) that the rings were composed of many small, unconnected particles, each orbiting near Saturn's equatorial plane. The classical designations for the rings are based on the gross ring components identified from the ground, but the Voyager spacecraft have shown the ring system to be highly structured. The radial particle-density distribution changes over distances of hundreds of meters, but individual particles, whose estimated sizes range from tens to hundreds of centimeters, have not been resolved. The ring plane has a maximum thickness of 1 to 2 km (0.6 to 1.2 mi). Spectroscopy shows the presence of water ice, which probably covers rocky silicate cores. The dynamics of the rings are not presently well understood. The theory of satellite resonances predicts that particles whose orbital periods are integral fractions (such as 1/2 or 2/3) of the periods of the satellites become either locked into or perturbed out of a particular orbit, but only a few of the observed gaps can be explained in this manner. Voyager showed eccentric ringlets and asymmetrical kinks in some ringlets. The kinks in the F ring gave it a braided appearance, but despite the proximity of two small satellites, the kinks do not seem directly related to them. Voyager also showed irregular spokelike features in the B ring that are composed of very small, strongly back-scattering particles temporarily out of the ring plane. Because of the detection of electrostatic discharges from the rings at radio wavelengths, these particles are thought to be electrically charged and thus forced out of the ring plane by Saturn's magnetic field. The rings may be the debris from satellites or comets broken apart by tidal forces (see ROCHE'S LIMIT). Another hypothesis is that Saturn's tidal forces and the perturbations of various satellites prevented the material left over from the formation of Saturn to accrete into further satellites. SATELLITES Saturn has the most extensive satellite system in the solar system. Not counting the myriad ring particles, more than 20 bodies orbiting around Saturn have so far been identified. Six can be easily seen through the telescope. TITAN is the largest Saturnian satellite and, among all solar-system satellites, is second in size only to the Jovian satellite Ganymede. It is the only satellite with a substantial atmosphere, although Neptune's TRITON has a much thinner one. The highest-resolution Voyager images show several haze layers that together obscure the surface. (For a discussion of this major satellite, see the article of that name.) The other satellites of Saturn tend to have low densities (1 to 1.5 g/cu cm, or 62 to 94 lb/cu ft) and high albedos, or surface reflectivities (0.4), indicative of water-ice-dominated bodies. Water frost has been detected spectroscopically on the surface of most of these satellites. With the exception of Phoebe, Iapetus, and Hyperion, they are in nearly circular, direct, low-inclination orbits. All of these satellites, with the exception of Enceladus, have highly cratered, old surfaces. The larger satellites have two distinct crater populations, perhaps a result of different sources and types of impacting bodies or of changes in the impact behavior of the satellite surfaces as they evolved. Mimas is dominated by a crater 130 km (81 mi) in diameter, or one-third of its own diameter. The impact that produced such a large crater on Mimas, weakly bound by its own gravity, was near the limit of major disruption. The remaining surface is heavily cratered and has some grooves that may have been either formed when the large crater was formed or developed by tidal interactions when Mimas was still warm from accretion. Using density measurements gathered by the Voyager 1 spacecraft, scientists have found that Mimas may have a small rocky core with a thick mantle of water ice. Enceladus is unusually smooth and free of craters. Its albedo is possibly the highest in the solar system, the result of a substantially resurfaced ice crust. Because the orbits of Dione and Enceladus are in resonance, the latter has an eccentricity forced by Dione. This produces strong tides and tidal heating, which may have kept the ice in a more fluid state during the postaccretion impact phase. The smoother regions have groove and ridge terrain that is very similar to regions on the icy Jovian satellite Ganymede. Tethys is heavily cratered and has an approximately 1,000-km-long (620-mi) valley running roughly north-south. The terraced walls of the valley suggest crustal layering. With a bulk density of 1.0 g/cu cm (62 lb/cu ft), Tethys is mostly water ice. It was subject to great expansion forces upon freezing that might have been responsible for the valley. Dione is about the same size as Tethys but has a higher density. High-albedo streaks or wisps on the dark trailing hemisphere may be frost deposits produced by water escaping from the interior through linear fractures. The crater density is generally lower than on Mimas. Like Tethys, Dione shows leading- and trailing-hemisphere asymmetries in albedos, probably caused by "gardening" effects due to the sweeping up of postaccretion-phase debris. Rhea also shows large albedo variations and has wispy markings like those seen on Dione. Differences in the size-frequency distribution of craters in bright and dark terrains indicate that the darker terrain is older. Hyperion is relatively small, irregular in shape, and heavily cratered. The long axis is not oriented toward the planet as would be expected in the dynamically stable case. Iapetus's albedo varies from 0.1 to 0.5 for the leading and trailing hemispheres respectively. The dark hemisphere is quite red, similar to the Jovian satellite Callisto. The dark leading hemisphere may be the result of selective impacts by carbonaceous chondritic material, but the albedo boundary is inexplicably sharp. Phoebe is in an eccentric, retrograde orbit expected of a body captured by the Saturn system rather than being formed there. It is a very-low-albedo, irregular-shaped body much like C-type asteroids. The coorbital satellites Epimetheus and Janus and 1980S3, occupy essentially the same orbit between Mimas and the F ring. Their orbital radii differ by less than their diameters, but collisions are prevented by their mutual gravitational interaction. These satellites, like all of the small ones, are both irregular in shape and cratered. They were perhaps once one body that was torn apart by a large impact. The satellite temporarily designated 1980S28 orbits just outside the A ring and acts as a gravitational barrier that defines the outer edge of that ring. The satellites 1980S27 and 1980S26 orbit just inside and outside of the F ring and probably confine the particles in that ring. These two "shepherding" satellites control the F ring. Telesto and Calypso are in orbits with periods nearly the same as that of Tethys; they are located near the stable LAGRANGIAN POINTS 60 degrees ahead (L4) and 60 degrees behind (L5) Tethys in its orbit. The satellite 1980S6 (Dione B) librates (oscillates) about the Dione L4 point and has an irregular shape. Bibliography: Briggs, Geoffrey, and Taylor, Fredric, The Cambridge Photographic Atlas of the Planets (1982; repr. 1986); Gehrels, Tom, and Matthews, Mildred S., eds., Saturn (1984); Hunt, Garry, and Moore, Patrick, Saturn (1982); Morison, David, Voyages to Saturn (1982); Nichols, R. G., "Voyages to the Worlds of Ice," Astronomy, December 1990; O'Meara, S. J., "Saturn's Great White Spot Spectacular," Sky & Telescope, February 1991; Soderblum, L. A., and Johnson, T. V., "The Moons of Saturn," Scientific American, January 1982; Washburn, Mark, Distant Encounters: The Exploration of Jupiter and Saturn (1983).[36;40;1m RINGS AND ESTABLISHED SATELLITES OF SATURN* --------------------------------------------------------------- Year of Name Discoverer Discovery -------------------------------------------------------------- D ring inner edge C ring inner edge B ring inner edge B ring outer edge A ring inner edge Encke division A ring outer edge Atlas Voyager 1 1980 Prometheus Voyager 1 1980 F ring Pioneer 11 1979 Pandora Voyager 1 1980 Epimetheus D. Cruikshank 1980 Janus D. Pascu 1980 G ring Mimas William Hershel 1789 E ring inner edge E ring maximum Enceladus William Hershel 1789 Telesto Note 1 1980 Tethys Giovanni Cassini 1684 Calypso Note 2 1980 E ring outer edge Electra P. Laques, J. Lecacheaux 1980 Dione Giovanni Cassini 1684 Rhea Giovanni Cassini 1672 Titan Christiaan Huygens 1655 Hyperion W. Bond, W. Lassell 1848 Iapetus Giovanni Cassini 1671 Phoebe William Pickering 1898 --------------------------------------------------------------- * Several other satellites are definitely known to exist, bringing the total number up to 24, and others are suspected. Little is known about these tiny moons, none more than about 18 km (11 mi) in diameter. One, identified in 1990 and named Pan in 1991, lies in Encke's division (1981S13). Three orbit between the outer edge of the E ring and Electra (1980S34, 1981S10, and 1981S11), and three orbit between the orbits of Dione and Rhea (1981S7, 1981S8, and 1981S9). Note 1--B. Smith, H. Reitsema, S. Larson, J. Fountain. Note 2--Space Telescope Wide Field/Planetary Camera Instrument Definition Team.
Saturn: Hubble pic
Saturn: Small Satellites