JUPITER

Photograph of Jupiter taken by Voyager 1 on Feb. 1, 1979, at a range of 32.7 million kilometres most massive of the planets, fifth in distance from the Sun. When ancient astronomers named the planet Jupiter, designated in astronomy, for the ruler of the gods in the Greco-Roman pantheon, they had no idea of the planet's true dimensions, but the name is appropriate, for Jupiter is larger than all the other planets combined. It has a narrow system of rings and 16 known satellites, one larger than the planet Mercury and 3 larger than the Earth's Moon. Jupiter also has an internal heat sourcei.e., it emits more energy than it receives from the Sun. This giant has the strongest magnetic field of any planet, with a magnetosphere so large that it would exceed the apparent diameter of the Moon if it could be seen from the Earth. Jupiter's system is the source of intense bursts of radio noise, at some frequencies occasionally radiating more energy than the Sun. Crescent view of Jupiter, a composite of three images taken by Voyager 1 on March 24, 1979. Knowledge about the Jovian system grew dramatically during the 1970s. The new information came in part from Earth-based observations but especially from two sets of spacecraftPioneers 10 and 11 in 197475 and Voyagers 1 and 2 in 1979. The Pioneer spacecraft served as scouts for the Voyagers, showing that the radiation environment of Jupiter was tolerable and mapping out the main characteristics of the planet and its environment. The more sophisticated instrumentation on the later spacecraft then filled in the details, providing so much new information that it was still being analyzed in 1995, when the Galileo spacecraft entered Jupiter's orbit and began a two-year mission (later extended to four) to study the planet and its satellites. also called Jove, Latin Iuppiter, Iovis, or Diespiter, the chief ancient Roman and Italian god. Like Zeus, the Greek god with whom he is etymologically identical (root diu, bright), Jupiter was a sky god. One of his most ancient epithets is Lucetius (Light-Bringer); and later literature has preserved the same idea in such phrases as sub Iove, under the open sky. As Jupiter Elicius he was propitiated with a peculiar ritual to send rain in time of drought; as Jupiter Fulgur he had an altar in the Campus Martius, and all places struck by lightning were made his property and were guarded from the profane by a circular wall. Throughout Italy he was worshiped on the summits of hills; thus, on the Alban Hill south of Rome was an ancient seat of his worship as Jupiter Latiaris, which was the centre of the league of 30 Latin cities of which Rome was originally an ordinary member. At Rome itself on the Capitoline Hill was his oldest temple; here there was a tradition of his sacred tree, the oak, common to the worship both of Zeus and of Jupiter, and here, too, were kept the lapides silices, pebbles or flint stones, which were used in symbolic ceremonies by the fetiales, the Roman priests who officially declared war or made treaties on behalf of the Roman state. Jupiter was not only the great protecting deity of the race but also one whose worship embodied a distinct moral conception. He is especially concerned with oaths, treaties, and leagues, and it was in the presence of his priest that the most ancient and sacred form of marriage (confarreatio) took place. The lesser deities Dius Fidius and Fides were, perhaps, originally identical and certainly were connected with him. This connection with the conscience, with the sense of obligation and right dealing, was never quite lost throughout Roman history. In Virgil's Aeneid, though Jupiter is in many ways as much Greek as Roman, he is still the great protecting deity who keeps the hero in the path of duty (pietas) toward gods, state, and family. But this aspect of Jupiter gained a new force and meaning at the close of the early Roman monarchy with the building of the famous temple on the Capitol, of which the foundations are still to be seen. It was dedicated to Iuppiter Optimus Maximus (i.e., the best and greatest of all the Jupiters), and with him were associated Juno and Minerva, in a fashion that clearly indicates a Greco-Etruscan origin, since the combination of three deities in one temple was foreign to the ancient Roman religion, while it is found in both Greece and Etruria. The temple's dedication festival fell on September 13, on which day the consuls originally succeeded to office, accompanied by the Senate and other magistrates and priests. In fulfillment of a vow made by their predecessors, the consuls offered to Jupiter a white ox, his favourite sacrifice, and, after rendering thanks for the preservation of the state during the past year, they made the same vow as that by which their predecessors had been bound. Then followed the feast of Jupiter. In later times this day became the central point of the great Roman games. When a victorious army returned home the triumphal procession passed to this temple. Throughout the Roman Republic this remained the central Roman cult; and, although Augustus' new foundations (Apollo Palatinus and Mars Ultor) were in some sense its rivals, that emperor was far too shrewd to attempt to oust Iuppiter Optimus Maximus from his paramount position; he became the protecting deity of the reigning emperor as representing the state, as he had been the protecting deity of the free republic. His worship spread over the whole empire. Jupiter, the fifth planet from the Sun and largest planet in the solar system. The Great Red Spot in astronomy, fifth major planet from the Sun, the largest nonstellar object in the solar system. It is named for the ruler of the gods in the Roman pantheon. Jupiter is 318 times as massive as the Earth, and its volume exceeds that of the latter by more than 1,500 times. Jupiter's enormous mass produces strong gravitational effects on other members of the solar system, including the formation of the Kirkwood gaps in the periods of asteroids, the tidal heating of the interior of the volcanic Galilean satellite Io, and the trajectory changes in cometary motions. Jupiter has at least 16 satellites, 4 of which were discovered by Italian astronomer Galileo Galilei in 1610. The planet and its moons, in effect, represent a miniature version of the solar system. Jupiter's diffuse ring system, which is less than 1 km (0.6 mile) thick, was discovered in 1979 by instruments on board the U.S. Voyager spacecraft. In 1995 Jupiter acquired its first artificial satellite, the Galileo spacecraft, which made detailed observations of the planet and its satellites, rings, and magnetosphere. Jupiter's northern and southern auroras, as observed by the Hubble Space Telescope.The auroras are Lightning storms on Jupiter, recorded by the Galileo spacecraft on Oct. 6, 1997, Spectroscopic research conducted over a wide range of the electromagnetic spectrum from Earth-based and Voyager instruments indicates that the planet is fluid, composed mainly of hydrogen and helium in near solar proportions. The planet emits nearly 70 percent more radiation in the infrared portion of the spectrum than it receives from the Sun. Laboratory experiments performed on hydrogen under a pressure of several million atmospheres indicate that the liquid region surrounding a solid, rocky core of approximately 10 Earth masses within Jupiter would be a highly conducting metallic allotrope. The planet's rapid rotation (9 hours 55 minutes 29.71 seconds) induces a variation in electric currents in the metallic hydrogen region that results in the largest magnetic field of any known planet, stretching 100 RJ (where RJ is Jupiter's equatorial radius of 71,492 km [44,423 miles]) on the sunward side (the magnetopause) and beyond the orbit of Saturn on the other side (the magnetotail). Charged particles, consisting of electrons, protons, and metallic ions (captured from Io's volcanic debris) are trapped by the magnetic field into narrow regions. This process results in the production of intense (Van Allen) radiation belts whose extent includes the six innermost satellites. The belts emit radio waves at a characteristic period used to define the planetary rotation rate. The interaction of charged particles from a flux tube connecting Io and Jupiter with the upper atmosphere of the planet triggers not only an extensive polar auroral display but also a number of polar electrical storms. Such storms were observed by cameras on board the Voyager and Galileo spacecraft as lightning superbolts. The highly coloured appearance of the visible cloud layers in Jupiter's atmosphere is thought to arise from the combined effects of electrical discharges and photochemical reactions (induced by solar radiation) of chemical constituents consisting primarily of ammonia, methane, ethane, ethylene, sulfur, and water vapour. Complex organic molecules have not been observed, and the rapid vertical motions at the cloud tops as well as the hostile radiation environment argue against the possible existence of organic life, as is known on the Earth, in Jupiter's atmosphere. Computer processing of Voyager images has revealed the magnitude and structure of the Jovian winds and the circulation of the atmosphere at the cloud tops. The banded appearance of the clouds is highly correlated with the location of wind speed maxima. In some respects, the global cloud-top circulation behaves like the Earth's atmosphere, with small-scale weather systems redistributing the energy associated with the uneven nature of the external solar heating. On the other hand, the longevity and symmetry of the wind profile around the equator and the breakdown of the regular cloud bands (both occurring at 45 latitude) suggests that stellar models of concentric cylindrical convection are a more plausible explanation of the cloud-top flow being primarily driven by internal heating. Jupiter's cloud bands may therefore more closely resemble the supergranulation cells observed on the Sun. Meteorologic research indicates that the Great Red Spot, the prominent oval-shaped area in the planet's clouds, is only unique for its longevity (over 300 years) and size (0.4 RJ 0.2 RJ), because its internal flow and interaction properties with other storm systems are entirely consistent with observations of all other oval features in the Jovian atmosphere. Research on the origin and evolution of the solar system has been conducted by using measurements of Jupiter's atmospheric composition, the surface cratering records of its Galilean satellites, and measurements of their physical properties (e.g., density). Such studies suggest that, though surface weathering has effaced much of their very early history, the Galilean satellites suffered meteoritic bombardment at about the same time that the lunar maria were formed. A spectacular example of the system's continuing susceptibility to bombardment occurred in July 1994, when more than 20 large fragments of the disintegrating Comet Shoemaker-Levy 9 crashed into the Jovian atmosphere, creating plumes and fireballs that yielded new clues to the nature of the planet's composition. Additional reading The standard reference for visual observations of Jupiter with telescopes of moderate size is still Bertrand M. Peek, The Planet Jupiter, 2nd ed., rev. by Patrick Moore. An extensive compilation of papers on all aspects of the Jovian system through 1975 is presented in Tom Gehrels (ed.), Jupiter (1976), which includes a discussion of the findings of Pioneers 10 and 11. Details regarding the Voyager mission itself may be found in David Morrison and Jane Samz, Voyage to Jupiter (1980). Tobias Chant Owen