In astronomy, sixth planet from the Sun. It is named after the Roman god of agriculture.
A brief treatment of Saturn follows.
Saturn is the second largest nonstellar object in the solar system, after Jupiter. It is about 95 times as massive as the Earth and has more than 700 times the volume. Saturn has at least 18 icy satellites, nine of which were discovered before 1900. It is also surrounded by an extensive ring system consisting of seven main rings.
Spectroscopic research conducted over a large range of the electromagnetic spectrum from a variety of observational platforms indicates that the outer layers of Saturn are gaseous; they are composed principally of hydrogen, with helium depleted by a factor of about two compared with the Sun. The planet emits approximately 80 percent more radiation in the thermal infrared portion of the electromagnetic spectrum than it receives from the Sun. Laboratory and computer modeling experiments performed on hydrogen under pressures of several million atmospheres indicate that it becomes a highly conducting liquid metal. Models of the interior of Saturn thus suggest that 10-20 percent of its mass resides in a rocky core that is surrounded by a shallow layer of liquid metallic hydrogen encased by an envelope of molecular hydrogen. The rapid rotation of the planetary liquid metallic core (10 hours 39 minutes 24 seconds) induces a variation in electric-current strength in this region that is manifested as a magnetosphere stretching 24 RS (where RS is Saturn's equatorial radius of 60,268 km [37,449 miles]) on the sunward side, the magnetopause, and 80 RS on the other side, the magnetotail. Charged particles consisting primarily of electrons, protons, and heavy ions--captured partly from the atmosphere of Saturn's largest satellite, Titan (q.v.)--are trapped by the planetary magnetic field into Van Allen radiation belts that enclose 13 of the planet's satellites and the ring system. Low-frequency radio waves are emitted at a characteristic period used to define the planetary rotation rate. Also emitted are sudden electrostatic discharges associated with the formation of narrow radial markings, called spokes, which are mostly confined to the outer region of the B ring. Narrow polar aurora produced by a cascade of charged particles sucked in from the solar wind do not appear to have the same spatial extent as their counterparts on Jupiter. Although it appears that lightning occurs in Saturn's atmosphere, no conclusive evidence has been brought forward as yet.
The inclination of Saturn's rotational axis to the ecliptic (i.e., the plane passing through the Sun and Earth) is approximately 27, nine times larger than that of Jupiter. Seasonal climatic changes are therefore likely, and tentative evidence exists for a one-season thermal lag manifested by the contrast in the appearance of the visible cloud tops in the two hemispheres. Spectroscopic evidence for a relatively large amount of photochemically unstable phosphine at the cloud-top level suggests that vigorous vertical mixing processes occur. This circumstance may help to account both for the production of stratospheric smogs and for the consequent apparent lack of distinctive large-scale cloud features at any but polar latitudes.
The circulation of the winds in Saturn's atmosphere is not highly correlated with the location of the cloud bands. Red- and brown-coloured ovals resembling Jupiter's Great Red Spot are observed at mid-latitudes, and a cloud feature morphologically similar to a classical fluid vortex street flow has been identified in photographs taken by the U.S. Voyager planetary probes.
Saturn's rings were first observed in 1610 by Galileo with the aid of a very primitive telescope in which they looked like "handles." By 1659 Christian Huygens, using an improved telescope, had deduced that Saturn was encircled by a flat ring structure, though he erroneously believed that the structure was solid and of considerable thickness. The rings average less than a few hundred metres in thickness and lie in the plane of the planet's equator, which has a fixed orientation in space. Because Saturn's equatorial plane is tilted by 27 from its orbital plane, the rings are seen from different angles as Saturn moves through its orbit, producing a variety of aspects that change from edge-on to opened-up about every 7 1/2 years. Because of their thinness, the rings cannot be seen edge-on. The rings are made up of countless separate particles of all sizes, ranging from grains of fine dust to bodies measuring possibly tens of kilometres across. The larger particles, which could even be called moons, are much less numerous. Individual particles have not been observed, but their sizes are inferred from the way they reflect sunlight and radar waves. Water ice has been observed on their surfaces, and it probably constitutes the bulk of the ring material. The particles are all in separate orbits around Saturn, with those closer to the planet moving more rapidly.
The main rings of Saturn are the central or B ring (from 1.5 to 2 RS); the outer or A ring (from 2.0 to 2.3 RS), separated from the B ring by a relatively empty region called the Cassini division; and the inner or C ring (from 1.2 to 1.5 RS). Each of these regions exhibits a great variety of fine structure, most likely because of different forms of gravitational effects by satellites outside or possibly within the rings. Other fainter rings, two of which (F and G) are very narrow and one (E) very broad, have recently been discovered around Saturn.
Saturn's rings may have formed in place by direct condensation of icy material from the cooling cloud of gas and dust that also formed the planet. Because of tidal effects, this material could never collect itself into a satellite. Alternatively, the rings may have resulted from the fragmentation of a satellite or satellites that entered the region of tidal destruction. Collisions with meteoroids may have contributed significantly to the breakup of such moons.
©Copyright Andrew Do