Saturn (redirected from 6th planet)

Saturn, in astronomy

Saturn, in astronomy, 6th planet from the sun.

Astronomical and Physical Characteristics of Saturn

Saturn's orbit lies between those of Jupiter and Uranus; its mean distance from the sun is c.886 million mi (1.43 billion km), almost twice that of Jupiter, and its period of revolution is about 29 1-2 years. Saturn appears in the sky as a yellow, starlike object of the first magnitude. When viewed through a telescope, it is seen as a golden sphere, crossed by a series of lightly colored bands parallel to the equator.

Saturn, like the other Jovian planets (Jupiter, Uranus, and Neptune), is covered with a thick atmosphere composed mainly of hydrogen and helium, with some methane and ammonia; its temperature is believed to be about −270°F; (−168°C;), suggesting that the ammonia is in the form of ice crystals that constitute the clouds. Like Jupiter's interior, Saturn's consists of a rocky core, a liquid metallic hydrogen layer, and a molecular hydrogen layer. Traces of various ices have also been detected. The wind blows at high speeds—reaching velocities of 1,100 mph (1,770 kph)—across Saturn. The strongest winds are found near the equator and blow mostly in an easterly direction. At higher latitudes, the velocity decreases uniformly and the winds counterflow east and west. Because no permanent markings on the planet are visible, the planet's exact period of rotation has not been determined. However, the period of each atmospheric band varies from 10 hr 14 min at the equator to about 10 hr 38 min at higher latitudes. This rapid rotation causes the largest polar flattening among the planets (over 10%). Saturn is the second largest planet in the solar system; its equatorial diameter is c.75,000 mi (120,000 km), and its volume is more than 700 times the volume of the earth. Its mass is about 95 times that of the earth, making Saturn the only planet in the solar system with a density less than that of water. Saturn has been encountered by four space probe missions: Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981), and Cassini and Huygens (2004). Among the discoveries made by the Voyager probes was a magnetosphere (a region of charged particles consisting primarily of electrons, protons, and heavy ions captured partly from the atmosphere of the satellite Titan) that encloses 13 of Saturn's satellites and its ring system. Huygens landed on Saturn's moon Titan in 2005 and returned photographs of its surface.

The Ring System

Saturn's most remarkable feature is the system of thin, concentric rings lying in the plane of its equator. Although first observed by Galileo in 1610, it was not until 1656 that the rings were correctly interpreted by Christiaan Huygens, who did not reveal his findings about their phases and changes in shape until his treatise Systema Saturnium was published in 1659. Saturn's rings were believed to be unique until 1977, when very faint rings were found around Uranus; shortly thereafter faint rings were also detected around Jupiter and Neptune.

Although the ring system is almost 167,770 mi (270,000 km) in diameter, it is only some 330 ft (100 m) thick. From earth, this system appears to consist mainly of two bright outer rings, denoted A and B, separated by a dark rift—discovered by the Italian-French astronomer Gian Domenico Cassini—known as Cassini's division, plus a third, faint inner crepe ring (denoted C). The Encke Division, or Encke Gap, which splits the A ring, is named after the German astronomer Johann Franz Encke, who discovered it in 1837. Pictures from the Voyager probes show four additional rings. The exceedingly faint D ring lies closest to the planet. The faint F Ring is a narrow feature just outside the A Ring. Beyond that are two far fainter rings named G and E. In 1859 the Scottish physicist James Clerk Maxwell showed that the rings must consist of countless tiny particles each orbiting the planet in accordance with the laws of gravitation. When edgewise to the earth the rings appear as a nearly imperceptible ribbon of light across the planet; this occurs twice during the 29 1-2-year period of revolution. Twice during each orbit the rings reach a maximum inclination to the line of sight, once when they are visible from above and once when visible from below.

The Voyager 1 (1980) and 2 (1981) space probes revealed incredible new detail as they passed within 78,000 mi (126,000 km) and 63,000 mi (101,000 km) of Saturn, respectively. They recorded hundreds of tiny rings that are grouped into the seven major rings. The three brightest rings are lettered from the outermost, A, B, and C. The A, B, and C rings dissolved into more than 1,000 narrow ringlets, 100 of which are in the Cassini division. The outer F ring was found to contain braids, knots, and strands, possibly caused by nearby moons that shepherd it, that is, limit the extent of a planetary ring through gravitational forces. The origin of the rings is unknown, although it is believed that they may have been formed from larger satellites that were shattered by the impact of comets and meteoroids.

The Satellite System

Saturn has 48 confirmed natural satellites. Because the increasing number of satellites makes it difficult to continue to name them after Greek Titans, a scheme was adopted for the outer satellites. These are now named after the giants of other cultures: Inuit, Norse, and Gallic. The satellites may be divided into eight groups for convenience. In the order of their distance from Saturn, the groups are shepherd (satellites whose orbit is within or just beyond Saturn's ring system), co-orbital (two satellites that share the same orbit and trade positions within it on a regular basis), inner large (large satellites within the E ring), Trojan (satellites that are co-orbital at Lagrangian points), outer large (large satellites beyond the E ring), and Inuit, Norse, and Gallic (each a group of outer satellites that have similar orbits).

There are four named satellites, Pan, Atlas, Prometheus, and Pandora in the shepherd group. The co-orbital group comprises Epimetheus and Janus. The inner large group comprises six satellites, Mimas, Methone, Pallene, Enceladus, Tethys, and Dione. The Trojan group comprises four satellites, Telesto, Calypso, Helene, and Polydeuces. The outer large group comprises four satellites, Rhea, Titan, Hyperion, and Iapetus. The Inuit group comprises five satellites, four of which—Kiviuq, Ijiraq, Paaliaq, and Siarnaq—have been named. Of the 18 satellites comprising the Norse group, only seven are named: Phoebe, Skathi, Mundilfari, Narvi, Suttungr, Thrymr, and Ymir. The Gallic group consists of three satellites, Albiorix, Erriapo, and Tarvos.

Almost all of Saturn's inner moons form a regular system of satellites; that is, their orbits are nearly circular and lie in the equatorial plane of the planet; almost all of the outer moons' orbits are inclined. Except for Hyperion, which has a chaotic orbit, and Phoebe, all the satellites are believed to have synchronous orbits; that is, their orbital and rotational periods are the same, so that they always keep the same face turned toward Saturn. The largest satellite, Titan, is 3,200 mi (5,150 km) in diameter and has the size and cold temperatures necessary to retain an atmosphere; it is the only natural satellite in the solar system with a substantial atmosphere.

Saturn has six major icy satellites that can be easily seen through earth-based telescopes. The most prominent feature of heavily cratered Mimas, the innermost of the six, is a large impact crater about one third the diameter of the satellite. Certain broad regions of Enceladus are uncratered, indicating geological activity that has resurfaced the satellite within the last 100 million years. Tethys also has a very large impact crater, as well as an extensive series of valleys and troughs that stretches three quarters of the way around the satellite. Both Dione and Rhea have bright, heavily cratered leading hemispheres and darker trailing hemispheres with wispy streaks that are thought to be produced by deposits of ice inside surface troughs or cracks. Iapetus, the outermost of the large icy satellites, has a dark leading hemisphere and a bright trailing hemisphere.

The remaining satellites, some sharing orbits with others, are smaller. The two largest of these, the dark-surfaced Phoebe and the irregularly shaped Hyperion, orbit far from the planet; the outermost satellite, Ymir, orbits with retrograde motion, i.e., opposite to that of the planet's rotation, as do Phoebe, Mundilfari, Narvi, Suttungr, Thrymr, and many of the newly discovered, yet unnamed satellites. The smallest, ranging from c.12 to 20 mi (20 to 32 km) in diameter, are Pan and Atlas, the satellites closest to the planet, and Telesto, Calypso, and Helene. Prometheus and Pandora, c.55 mi (90 km) in diameter, share an orbit, as do Epimetheus and Janus.

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Saturn, in Roman religion and mythology

Saturn, in Roman religion and mythology, god of harvests, later identified with the Greek Kronos. Little is known of the origins of his cult. His reign was regarded as the Golden Age. He was the husband of Ops and the father of Jupiter, Juno, Ceres, Pluto, and Neptune. It was said that after the fall of the Titans, Saturn fled to Italy, where he settled on the Capitoline Hill, civilized the people, and taught them the arts of agriculture. At his festival, the Saturnalia, held at first on Dec. 17 but later extended for several days thereafter, gifts were exchanged, schools and courts were closed, war was outlawed, and slaves and masters ate at the same table.

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Saturn

Roman god of agriculture, equated with the Greek deity Cronus. His wife was Ops, the goddess of plenty, and his children included Juno, Neptune, and Ceres. His festival, Saturnalia (beginning December 17), became the most popular Roman festival; its influence is still felt in the celebration of Christmas and the Western New Year. During Saturnalia, all business transactions were suspended, presents were exchanged, and slaves were given token freedom. The remains of Saturn's temple are located in the Forum in Rome. Saturday is named for Saturn.

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Saturn

Sixth planet from the Sun, named for the Roman god of sowing and seed. The second largest nonstellar object in the solar system after Jupiter, it is about 95 times as massive as Earth and has more than 700 times its volume. Saturn's outer layers are gaseous, mainly hydrogen. Models of its interior suggest a rock-and-ice core surrounded by a shallow layer of liquid metallic hydrogen encased by an envelope of molecular hydrogen. Its mean density, about 70% that of water, is the lowest of any known object in the solar system. Saturn has at least 47 moons (including Titan, the largest) and an extensive ring system, with several main sections visible from Earth with a telescope. Saturn's rings, first observed in 1610 by Galileo, are made up of countless separate particles ranging mainly from inches to many feet in size but also including dust in some regions. Water ice probably constitutes most of the ring material. Saturn's day is about 10.6 hours; its year is 29.4 Earth years. Its rapid rotation, acting on electric currents in the core, generates a strong magnetic field and large magnetosphere. Saturn's fast spin also makes it the most flattened (oblate) of the planets; its polar diameter of 67,560 mi (108,728 km) is 10% smaller than its equatorial diameter. Its average distance from the Sun is 887 million mi (1.43 billion km).

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Saturn

Any of a series of space launch vehicles developed by the U.S. beginning in 1958 for the Apollo Moon-landing program. Saturn I, the first U.S. rocket specifically developed for spaceflight (first fired 1961), was a two-stage vehicle that placed unmanned versions of Apollo spacecraft and other satellites into Earth orbit. An upgraded version, Saturn IB, was used for unmanned and manned Apollo Earth-orbital missions and for ferrying crews to the Skylab space station. The three-stage Saturn V, the largest launch vehicle ever built by the U.S., was used for manned Apollo lunar flights and to launch Skylab.

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Saturn¹

the Roman god of agriculture and vegetation

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Saturn²

1. one of the giant planets the sixth planet from the sun, around which revolve planar concentric rings (Saturn's rings) consisting of small frozen particles. The planet has at least 30 satellites. Mean distance from sun: 1425 million km; period of revolution around sun: 29.41 years; period of axial rotation: 10.23 hours; equatorial diameter and mass: 9.26 and 95.3 times that of the earth, respectively

2. a large US rocket used for launching various objects, such as a spaceprobe or an Apollo spacecraft, into space

3. the alchemical name for lead

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Saturn [′sad·ərn]

(aerospace engineering)

One of the very large launch vehicles built primarily for the Apollo program; begun by Army Ordnance but turned over to the National Aeronautics and Space Administration for the manned space flight program to the moon.

(astronomy)

The second largest planet in the solar system (mass is 95.2 compared to earth's 1) and the sixth in the order of distance to the sun; it is visible to the naked eye as a yellowish first-magnitude star except during short periods near its conjunction with the sun; it is surrounded by a series of rings.

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Saturn 

in ancient Roman religion and mythology, the god of seed sowing. He was identified with the ancient Greek god Cronus. Annual festivals were held in Saturn’s honor.

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Saturn 

the sixth major planet from the sun in the solar system; its astronomical symbol is b. Saturn is one of the giant planets. The semimajor axis of its orbit, that is, the mean distance from the sun, is 9.54 astronomical units, or 1.43 billion km. The eccentricity of its orbit is 0.056, the largest among the giant planets. The orbit is inclined 2°29’ to the plane of the ecliptic. Saturn completes one revolution around the sun (sidereal period of revolution) in 29.458 years at an average velocity of 9.64 km/sec. Its synodic period of revolution is equal to 378.09 days. In the sky Saturn appears as a yellowish star, whose brightness ranges from stellar magnitude 0 to 1 (at mean opposition). The high variability of its brightness is due to the existence of rings around the planet; the angle between the plane of the rings and the direction to the earth varies from 0° to 28°, and an observer on the earth sees the rings at different angles, which determines the variation in the planet’s brightness. The visible disk of Saturn has the shape of an ellipse, with axes of 20.7” and 14.7” (at mean opposition). At superior conjunction, the visible dimensions of Saturn are 25 percent smaller, and the brightness is 0.48 stellar magnitude fainter. Saturn’s visual albedo is equal to 0.69.

The ellipticity of Saturn’s disk is the result of a spheroidal object undergoing rapid rotation: Saturn’s period of rotation about its axis is 10 hr 14 min at the equator, 10 hr 38 min at middle latitudes, and 10 hr 40 min at a latitude of approximately 60°. The axis of rotation is inclined to the planet’s orbital plane at an angle of 63°36’. In linear units, Saturn’s equatorial radius is 60,100 km, its polar radius is 54,600 km (to an accuracy of approximately 1 percent), and its oblateness is equal to 1: 10.2. Saturn’s volume exceeds the earth’s by a factor of 770, and its mass is 95.28 times greater than the earth’s (5.68 × 10²⁶ kg); thus, its average density is 0.7 g/cm³ (half as much as the density of the sun). With respect to the sun, Saturn’s mass is 1:3,499. The acceleration of the force of gravity on Saturn’s surface, measured at the equator, is equal to 9.54 m/sec². The escape velocity on the planet’s surface reaches 37 km/sec.

Few details are visible on the disk of Saturn, even when the planet is viewed under optimum conditions. Only light and dark bands parallel to the equator can be seen. Dark or light patches are infrequently seen superimposed on these bands; they are useful in determining the planet’s rotation.

According to measurements of the heat flux emanating from the planet in the infrared region of the spectrum, which corresponds to the thermal flux from the sun, Saturn’s surface temperature ranges between - 190°C and - 150°C (above the equilibrium temperature of - 193°C). This indicates that the planet’s thermal radiation contains a fraction of internally generated heat, which is confirmed by measurements of the radio-frequency radiation.

The difference in Saturn’s angular rates of rotation at different latitudes indicates that the surface observed from the earth is only the outer cloud layer of the atmosphere. Some idea of the planet’s internal structure can be formed on the basis of theoretical studies. The observed perturbations in the motions of Saturn’s satellites, when compared with the planet’s oblateness and with its average density, make it possible to determine the approximate pressure and density variations in the interior (seePLANET). Saturn’s very low average density indicates that it, like the other giant planets, consists primarily of light gases—hydrogen and helium—which are also predominant on the sun. Saturn’s composition is presumed to include hydrogen (80 percent) and helium (18 percent); the heavier elements, concentrated in the planet’s core, amount to only 2 percent. To depths of about half the planet’s radius, hydrogen is found in the molecular phase; at greater depths, because of the tremendous pressures, hydrogen enters the metallic phase. At the center of Saturn the temperature is close to 20,000°K.

The chemical composition of the atmosphere above Saturn’s cloud layer is determined from the absorption lines of the planet’s spectrum. Molecular hydrogen (40 km-atmospheres) forms the principal part, methane (CH₄) is indisputably present (0.35 km-atmosphere), and the existence of ammonia (NH₃) is hypothesized, although it may be present in the clouds in the form of aerosols. There is reason to believe that Saturn’s atmosphere also contains helium, which is not spectroscopically detected in the spectral region accessible to us. No magnetic field has been found for Saturn.

A remarkable feature is the rings of Saturn—concentric formations of varying brightness that appear as if fitted inside each other, forming a single planar system of slight thickness lying in the planet’s equatorial plane. A ring around Saturn was first observed by Galileo in 1610, but because of the poor quality of the telescope he mistook the portions of the ring visible at the edges of the planet for satellites of Saturn. A correct description of Saturn’s ring was given by C. Huygens (1659), and soon afterward J. Cassini showed that it consisted of two concentric components—rings A and B, separated by a dark interval (Cas-sini’s division). Much later, in 1850, the American astronomer W. Bond discovered a faint, inner ring (C), and in 1969 a still fainter ring close to the planet—ring D—was detected. The brightness of ring D does not exceed 1/20 the brightness of the brightest ring—ring B. Ring A extends from 138,000 to 120,000 km above the surface of the planet; B, from 116,000 to 90,000 km; C, from 89,000 to 75,000 km; and D, from 71,000 km almost to the surface. The nature of the rings became clear after the British physicist J. Maxwell (in 1859) and the Russian mathematician S. V. Kovalevskaia (in 1885) proved by different methods that a stable ring around a planet can exist only if the ring consists of a number of individual small bodies; a continuous solid or fluid ring would be broken up by the planet’s gravitational force.

This theoretical conclusion, drawn in the late 19th century, was empirically confirmed independently by A. A. Belopol’skii (Russia), J. Keeler (USA), and H. Deslandres (France), who photographed the spectrum of Saturn by means of a slit spectrograph. They found, on the basis of the Doppler-Fizeau principle, that the outer portions of Saturn’s ring system rotate more slowly than the inner portions. The measured speed proved to be equal to the speeds Saturn’s satellites would have if they were located at the same distances from the planet.

Over a period of 29.5 years the rings of Saturn are twice visible from earth at maximum exposure, and twice there are periods when the sun and the earth are in the plane of the rings. On the latter occasions either the rings are illuminated edgewise by the sun, or they are visible edgewise to an observer on the earth. At such times, the rings are practically invisible, which indicates their very small thickness. Various investigators, relying on visual and photometric observations and on the theoretical analysis of them, draw the conclusion that the average thickness of the rings ranges from 10 cm to 10 km. Of course, a ring of such thickness cannot be seen edgewise from the earth. The dimensions of the solid bodies in the ring are estimated at 10^-1 to 10³ cm, with a predominance of bodies approximately 1 m in diameter. This is confirmed by the observed reflection of radio waves reflected from Saturn’s rings.

The chemical composition of the matter in the rings is apparently the same for all four sections; only the degree to which each is filled with bodies varies. The spectrum of the rings differs significantly from that of Saturn itself and from that of the sun by which the rings are illuminated. It indicates an increased reflectance of the rings in the near-infrared region (2.1 and 1.5 micrometers) corresponding to reflection from ice (H₂O). It may be assumed that the bodies forming the rings either are covered with ice or frost or consist of ice. In the latter case, the mass of all the rings may be estimated at 10²⁴ g, that is, five orders of magnitude less than the mass of the planet itself. The temperature of Saturn’s rings is apparently close to the equilibrium temperature, that is, 80°K.

Saturn has ten satellites. One of them—Titan—has dimensions comparable to those of the planets; its diameter is 5,000 km, and its mass is 2.4 × 10^-4 times the mass of Saturn. Titan has an atmosphere containing methane. The satellite closest to the planet is Janus, which was discovered in 1966. It revolves around the planet in 18 hr at an average distance of 160,000 km, and its diameter is approximately 220 km. The most distant satellite is Phoebe. It revolves around Saturn in a retrograde direction at a distance of approximately 13 million km.

REFERENCES

Sharonov, V. V. Prirodaplanet. Moscow, 1958.
Moroz, V. I. Fizikaplanet. Moscow, 1967.
Bobrov, M. S. Kol’tsa Saturna. Moscow, 1970.
Fizicheskie kharakteristiki planet-gigantov. Alma-Ata, 1971.
Zharkov, V. N. Vnutrennee stroenie Zemli, Luny i planet. Moscow, 1973.

D. IA. MARTYNOV

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Saturn 

the name of a series of American launch vehicles developed between 1964 and 1967 for the Apollo programs; the series included the Saturn 1, Saturn 1B, and Saturn 5 models.

The Saturn 1 was an experimental, two-stage launch vehicle used for development work on certain subassemblies common to all launch vehicles and also for the orbital injection of models of the Apollo spacecraft. It had a launch weight without pay-load of 502 tons, a diameter of 6.58 m (12 m including stabilizer fins), and a length of 38.1 m. It was capable of injecting a pay-load of up to 10.2 tons into a geocentric, circular orbit with an altitude of 185 km. The propulsion system of the first stage consisted of eight liquid-propellant rocket engines, having a total thrust of 6.8 meganewtons (MN) (1 MN = 100 tons-force) and operating on liquid oxygen and kerosine. The engine of the Thor ballistic missile was the basis for these liquid-propellant rocket engines. Those on the outer edge of the installation were mounted on hinged suspensions at an angle to the axis of the rocket and were used to control the rocket through three axes. The second stage had six liquid-propellant rocket engines, having a total thrust of 40.8 kilonewtons (kN) and operating on liquid oxygen and liquid hydrogen. These engines had been used previously on the Atlas-Centaur launch vehicle. There was a total of six launchings of the Saturn 1.

The Saturn 1B was a two-stage launch vehicle designed for development work on unmanned and manned Apollo spacecraft in geocentric orbits, for the delivery of astronauts to the Skylab space station, and for spacecraft launchings in the Apollo-Soyuz program. It had a launch weight of approximately 570 tons, a diameter of 6.6 m, and a length of 43.3 m. It was capable of injecting a payload of 18.1 tons into a circular, geocentric orbit with an altitude of 195 km. The first stage used a modified first stage from the Saturn 1 and had a total thrust when operating on liquid oxygen and kerosine of 7.44 MN. The second stage had a single liquid-propellant rocket engine operating on liquid oxygen and liquid hydrogen with a thrust of 1.043 MN. In order to control the banking of the rocket, two installations were mounted on the second stage, each with three auxiliary engines, having a thrust of 680 kN and operating on nitrogen tetroxide and unsymmetrical dimethylhydrazine. There was a total of seven launchings on the Saturn 1B.

The Saturn 5 was a three-stage launch vehicle. It was designed for development work on a fully equipped Apollo spacecraft in geocentric and selenocentric orbits, as well as for the delivery of astronauts to the moon. Its launch weight was as much as 2,950 tons, its length was 85.6 m without payload and approximately 110 m with payload, and its diameter was 10.1 m (19.2 m including stabilizer fins). It was capable of injecting a payload of approximately 130 tons into a circular, geocentric orbit with an altitude of 195 km; it could launch up to 48.8 tons into a lunar trajectory. The propulsion system of the first stage comprised five liquid-propellant rocket engines, operating on liquid oxygen and kerosine and having a total thrust of 34.33 MN. The second stage had five liquid-propellant rocket engines, with a total thrust of 5.2 MN, and the third stage had one liquid-propellant rocket engine, with a thrust of 1.043 MN; the third stage was similar to the second stage of the Saturn 1B, but there were some design differences. The liquid-propellant rocket engine used liquid oxygen and liquid hydrogen.

There was a total of 12 launchings of the Saturn 5, including seven for lunar missions and one launching of the manned space station Skylab into a geocentric orbit.

The Saturns were assembled in the vertical position inside a building more than 5 km from the launching pad. The launching vehicles were assembled on the launch stand, which served as a launch pad.

G. A. NAZAROV