Jupiter

Jupiter is the largest planet in the solar system and is easily visible in the night sky. Jupiter's mass (1.9 × 10²⁷kilograms [4.2 × 10²⁷ pounds]) is nearly two and a half times the mass of the rest of the solar system's planets combined. Jupiter's volume, filled mostly with gas, is 1,316 times that of Earth. The fifth planet from the Sun, Jupiter's year is 11.86 Earth years but its day is short, only nine hours and fifty-five minutes. Jupiter resembles a small star: its composition, like the Sun's, is mostly hydrogen and helium. It emits about twice the energy that it receives from the Sun and puts out over 100 times more heat than Earth. If Jupiter had been about 50 to 100 times larger, it might have evolved into a star rather than a planet.

Historic Observations of Jupiter

Jupiter has intrigued humans since antiquity. It is named for the king of the Roman gods, and most of its twenty-eight moons are named after the god's many lovers. In 1609 and 1610, Italian mathematician and astronomer Galileo Galilei and German astronomer Simon Marius began telescopic studies of Jupiter and its system. Galileo is credited with the discovery of Jupiter's four largest moons: Io, Europa, Ganymede, and Callisto, now called the Galilean satellites in his honor. These moons had an impact on the thinking of those times. It was believed then that Earth was the center of the universe and that all the planets and moons revolved around Earth. Galileo's observations showed that the four moons revolved around Jupiter, not Earth. This discovery contributed to Galileo's doom. He was condemned by the Catholic Church, forced to recant his discovery, and only in 1992 did Pope John Paul II agree that Galileo was right to support Copernicanism.

As telescopes improved, other astronomers continued to observe Jupiter and to study its colorful bands and the long-lived storm known as the Great Red Spot. Twenty-four other smaller satellites have been discovered, from Amalthea in 1892 to Leda in 1974 to twelve new moons in 2001. Observations from Earth showed that Jupiter has a massive magnetosphere and that the planet emits radiation at radio wavelengths . From this, astronomers deduced that Jupiter is surrounded by radiation belts , similar to Earth's Van Allen radiation belts , and that the planet must have a strong magnetic field.

Spacecraft Explorations

Space missions allowed scientists to make great leaps forward in the exploration of Jupiter and its moons. The first spacecraft to fly by Jupiter were Pioneer 10 (in 1973) and Pioneer 11 (in 1974). They passed as close as 43,000 kilometers (26,660 miles) from Jupiter. Their suite of instruments made important observations of the atmosphere, magnetosphere, and space environment around the planet. In 1979 the spacecraft Voyager 1 and Voyager 2 passed close to Jupiter and its moons, making startling discoveries that included auroras on Jupiter, a ring system surrounding the planet, and active volcanoes on the moon Io.

In 1995, the Galileo spacecraft became the first to orbit Jupiter. It dropped a probe into the planet that survived for 57.6 minutes, until it was crushed by Jupiter's enormous pressure. The probe's instruments sent back valuable information on the temperature, pressure, composition, and density of the upper atmosphere.

The Galileo probe provided scientists with their first glimpse inside the top layers of the atmosphere. One surprising discovery was that Jupiter has thunderstorms that are many times larger than those on Earth. The cause of the thunderstorms is the vertical circulation of water vapor in the top layers of Jupiter's atmosphere.

The main Galileo spacecraft has been making observations of Jupiter, its moons, and its environment since 1995, and these were slated to continue until 2002. Scientific observations continue to be made using Earth-based telescopes and the Hubble Space Telescope, which is in orbit around Earth. The combination of many sets of observations over time is extremely valuable for understanding Jupiter and its system.

The Atmosphere and Interior of Jupiter

Jupiter's atmosphere has alternating patterns of dark and light belts and zones. Within these belts and zones are gigantic storm systems such as the Great Red Spot. The locations and sizes of the belts and zones change gradually over time, and many of them can be seen through a telescope. The Great Red Spot has lasted for at least 100 years, and probably as long as 300 years. It rotates counterclockwise every six days, and this direction, plus its location in the southern hemisphere, indicates that it is a high-pressure zone. This differs from the cyclones that occur on Earth, which are low-pressure zones. The red color of the spot is something of a mystery. Several chemicals, including phosphorus, have been suggested as the cause of the red color but, on the whole, the reasons for Jupiter's different colors are not yet understood.

The atmosphere of Jupiter consists of about 81 percent hydrogen and 18 percent helium, with small amounts of methane, ammonia, phosphorus, water vapor, and various hydrocarbons. Observations by Galileo showed a cloud of fresh ammonia ice downstream from the Great Red Spot. Jupiter's atmosphere has strong winds, but the mechanisms that drive them are not well understood. There are at least twelve different streams of prevailing winds, and they can reach velocities of up to 150 meters per second (492 feet per second) at the equator. On Earth, winds are driven by large differences in temperature, differences that do not exist, at least not on the top part of Jupiter's atmosphere, where the temperature at the poles is about the same as that at the equator (-130°C [-202°F]).

The cloud layer, which is thought to be only about 50 kilometers (31 miles) thick, comprises only a small part of the planet. What is the interior of Jupiter like? The pressure inside Jupiter, which increases with depth, is enormous—it may reach about 100 million times the pressure on Earth's surface. Although we cannot directly observe Jupiter's interior, theory plus observations of the atmosphere and the surrounding environment suggest that below the cloud layer there is a 21,000-kilometer-thick (13,000-mile-thick) layer of hydrogen and helium. This layer gradually changes from gas to liquid as the pressure increases. Beneath this layer is a sea of liquid metallic hydrogen about 40,000 kilometers (24,800 miles) deep. Metallic hydrogen does not form on Earth, because our planet lacks the extreme pressures necessary to break up the hydrogen molecules and pack them so tightly that they break up and become electrically conductive. This electrically conductive metallic hydrogen is what drives Jupiter's strong magnetic field. Deeper still in Jupiter's interior is the core, which may be solid and rocky. It is estimated that the core is about one and a half times Earth's diameter, but ten to thirty times more massive. It is also very hot: about 30,000°C (54,000°F). This heat comes up through the layers and is detected at "hot spots" in the atmosphere, which are cloud-free holes.

Magnetic Field and Rings

Jupiter's sea of metallic hydrogen causes it to have the strongest magnetic field of any planet in the solar system. The field is inverted relative to Earth's, that is, a compass there would always point south. The region around the planet that is dominated by the magnetic field is called the magnetosphere. The stream of charged particles sent by the solar wind causes Jupiter's magnetosphere to be shaped like a teardrop, pointing directly away from the Sun. Inside the magnetosphere is a swarm of ions, protons , and electrons , which are called plasma. The plasma rotates along with Jupiter's magnetic field, blasting off charged particles. Some of them impact on the surfaces of the moons. On Io, volcanoes eject material into space, and the particles get caught up in Jupiter's magnetosphere. This creates a doughnut-shaped region of charged particles at about the distance from Jupiter of Io's orbit. This is called the Io plasma torus. It was first observed by the Pioneer spacecraft.

The Voyager missions showed that Jupiter is surrounded by faint rings. Unlike Saturn's rings, which are made up of icy particles, Jupiter's rings are made up of small dust particles. Two small satellites, Adrastea and Metis, are embedded within the rings. Observations by Galileo spacecraft showed that the dust comes from meteoroids impacting the satellites closest to Jupiter.

The Galilean Satellites

The Galilean satellites are all different from one another. Io and Europa have greater densities than Ganymede and Callisto, suggesting that the two inner moons (Io and Europa) contain more rock, and the outer moons more water ice.

Io.

Io is the most volcanically active body in the solar system. It is the only place outside Earth where eruptions of hot magma have been observed. Other planets and moons in the solar system have been volcanically active in the distant past. Io is about the same size as Earth's Moon and, had it not been for its peculiar orbit, it too would have cooled down and volcanism would have ceased. Tidal stresses are produced within Io as a result of the gravitational pull of Jupiter, Europa, and Ganymede. These stresses cause the interior of Io to heat up, leading to active volcanism. About 100 active volcanoes have been seen so far on Io, many of which were discovered from their thermal signature in infrared observations made by the Galileo spacecraft. Some of the active volcanoes have plumes that can reach 300 kilometers (186 miles) high. Io's surface is very young as a result of many continuous volcanic eruptions, and no impact craters have been seen. The colors of the surface—vivid reds, yellows, greens, and black—are different from those seen on other solid bodies in the solar system. These colors are a result of sulfur and silicates on the surface. Io's lavas are hotter than those seen on Earth today, reaching temperatures of 1,500°C (2,700°F). They may be similar in composition to ultramafic lavas on Earth, which erupted millions of years ago.

Europa.

Europa is particularly intriguing because of the possibility that it might harbor life. Observations by Galileo spacecraft showed that Europa's cracked surface resembles the ice floes seen in Earth's polar regions. High-resolution images show that some of the broken pieces of the ice crust have shifted away from one another, but that they fit together like a jigsaw puzzle. This suggests that the crust has been, or still is, lubricated from underneath by warm ice or liquid water. The two most basic ingredients for life are water and heat. Like Io, Europa is subject to tidal stresses because of

Jupiter and Ganymede's gravitational pull. While Europa has no evidence of current active silicate volcanism, the tidal stresses may cause heating of the interior, providing the other key ingredient for life. Europa's surface does show evidence of ice volcanism. There are places where material appears to have come up from underneath as slushy ice and flowed on the surface. Europa has very few impact craters, indicating that its surface is young. Slushy ice flowing over the surface probably erased many impact craters. Europa's surface composition is dominated by water, but Galileo detected other compounds, including hydrogen peroxide (H₂O₂) on the surface and a thin oxygen atmosphere. The behavior of Jupiter's magnetic field around Europa implies that there may be ions circulating globally beneath the icy surface.

Ganymede.

Larger than the planets Mercury and Pluto, Ganymede was the first moon known to have a magnetic field, one of the earliest discoveries made by the Galileo mission. The field is stronger than that of Mercury. Ganymede has a core made up of metallic iron or iron sulfides. If the core is molten and moving, it would produce the strong magnetic field observed by Galileo. Ganymede's surface shows a complex geologic history. The surface is characterized by large dark areas and by bright grooved terrains. The grooves are thought to have formed when the crust separated along lines of weakness. Other images showed hillcrests and crater rims capped by ice, and old terrain cut by furrows and marked by impact craters. Observations in the ultraviolet made from the Hubble Space Telescope showed the presence of oxygen on Ganymede, and Galileo observations detected hydrogen escaping from Ganymede into space. These results indicate that Ganymede has a thin oxygen atmosphere. Astronomers believe that the atmosphere is produced when charged particles trapped in Jupiter's magnetic field come down to Ganymede's surface. The charged particles penetrate the icy surface, disrupting the water ice. The hydrogen escapes into space, whereas the heavier oxygen atoms are left behind.

Callisto.

About the same size as the planet Mercury, Callisto is Jupiter's second largest moon. Its surface is heavily cratered, implying that it is extremely old, probably dating from about 4 billion years ago, which is close to the time when the solar system formed. Callisto's surface is icy and has some large impact craters and basins surrounded by concentric rings. The largest impact basin is called Valhalla, and it has a bright central region 600 kilometers (372 miles) in diameter, with rings extending to 3,000 kilometers (1,860 miles) in diameter. Galileo observations showed that Callisto has a magnetic field. Underneath its icy crust, Callisto may have a liquid ocean, which, if it is as salty as Earth's oceans, could carry enough electrical currents to produce the magnetic field. A major discovery made by the Galileo mission is that Callisto has a thin atmosphere of carbon dioxide.

see also Exploration Programs (volume 2); Galilei, Galileo (volume 2); NASA (volume 3); Planetary Exploration, Future of (volume 2); Robotic Exploration of Space (volume 2); Shoemaker, Eugene (volume 2); Small Bodies (volume 2).

Rosaly M. C. Lopes

Bibliography

Beatty, J. Kelly, Carolyn Colins Petersen, and Andrew Chaikin, eds. The New Solar System, 4th ed. Cambridge, UK: Sky Publishing Corporation and Cambridge University Press, 1999.

Shirley, James. H., and Rhodes. W. Fairbridge, eds. Encyclopedia of Planetary Sciences. London: Chapman & Hall, 1997.

Internet Resources

NASA Jet Propulsion Laboratory, California Institute of Technology. <http://jpl.nasa.gov/>.

Jupiter , in astronomy, 5th planet from the sun and largest planet of the solar system.

Astronomical and Physical Characteristics

Jupiter's orbit lies beyond the asteroid belt at a mean distance of 483.6 million mi (778.3 million km) from the sun; its period of revolution is 11.86 years. In order from the sun it is the first of the Jovian planets—Jupiter, Saturn , Uranus , and Neptune —very large, massive planets of relatively low density, having rapid rotation and a thick, opaque atmosphere. Jupiter has a diameter of 88,815 mi (142,984 km), more than 11 times that of the earth. Its mass is 318 times that of the earth and about 2 1/2 times the mass of all other planets combined.

The atmosphere of Jupiter is composed mainly of hydrogen, helium, methane, and ammonia. However, the concentration of nitrogen, carbon, sulfur, argon, xenon, and krypton—as measured by an instrument package dropped by the space probe Galileo during its 1995 flyby of the planet—is more than twice what was expected, raising questions about the accepted theory of Jupiter's formation. The atmosphere appears to be divided into a number of light and dark bands parallel to its equator and shows a range of complex features, including a storm called the Great Red Spot. Located in the southern hemisphere and varying from c.15,600 to 25,000 mi (25,000 to 40,000 km) in one direction and 7,500 to 10,000 mi (12,000 to 16,000 km) in the other, the storm rotates counterclockwise and has been observed ever since 1664, when Robert Hooke first noted it. Also in the southern hemisphere is the Little Red Spot, c.8,000 mi (13,000 km) across. It formed from three white-colored storms that developed in the 1940s, merged in 1998-2000, and became clearly red by 2006. Analysis of the data obtained when massive pieces of the comet Shoemaker Levy 9 plunged into Jupiter in 1994 has extended our knowledge of the Jovian atmosphere.

Jupiter has no solid rock surface. One theory pictures a gradual transition from the outer ammonia clouds to a thick layer of frozen gases and finally to a liquid or solid hydrogen mantle. Beneath that Jupiter probably has a core of rocky material with a mass 10-15 times that of the earth. The spot and other markings of the atmosphere also provide evidence for Jupiter's rapid rotation, which has a period of about 9 hr 55 min. This rotation causes a polar flattening of over 6%. The temperature ranges from about -190°F (-124°C) for the visible surface of the atmosphere, to 9°F (-13°C) at lower cloud levels; localized regions reach as high as 40°F (4°C) at still lower cloud levels near the equator. Jupiter radiates about four times as much heat energy as it receives from the sun, suggesting an internal heat source. This energy is thought to be due in part to a slow contraction of the planet. Jupiter is also characterized by intense nonthermal radio emission; in the 15-m range it is the strongest radio source in the sky. Jupiter has a huge asymetrical magnetic field, extending past the orbit of Saturn in one direction but far less in the direction of the sun. This magnetosphere traps high levels of energetic particles far more intense than those found within earth's Van Allen radiation belts . Six space probes have encountered the Jovian system: Pioneers 10 and 11 (1973 and 1974), Voyagers 1 and 2 (both 1979), Ulysses (1992), and Galileo (1995-2003).

Its Moons and Rings

At least 63 natural satellites orbit Jupiter. They are conveniently divided into six main groups (in order of increasing distance from the planet): Amalthea, Galilean, Himalia, Ananke, Carme, and Pasiphae. The first group is comprised of the four innermost satellites—Metis, Adrastea, Amalthea, and Thebe. The red color of Amalthea (diameter: 117 mi/189 km), a small, elongated satellite discovered (1892) by Edward Barnard , probably results from a coating of sulfur particles ejected from Io. Metis (diameter: 25 mi/40 km), Adrastea (diameter: 12 mi/20 km), and Thebe (diameter: 62 mi/100 km) are all oddly shaped and were discovered in 1979 in photographs returned to earth by the Voyager 1 space probe. Metis and Adrastea orbit close to Jupiter's thin ring system; material ejected from these moons helps maintain the ring.

The four largest satellites—Io, Europa, Ganymede, and Callisto—were discovered by Galileo in 1610, shortly after he invented the telescope, and are known as the Galilean satellite group. Io (diameter: 2,255 mi/3,630 km), the closest to Jupiter of the four, is the most active geologically, with 30 active volcanoes that are probably energized by the tidal effects of Jupiter's enormous mass. Europa (diameter: 1,960 mi/3,130 km) is a white, highly reflecting body whose smooth surface is covered with dark streaks up to 43 mi/70 km in width and from several hundred to several thousand miles in length. Ganymede (diameter: 3,268 mi/5,262 km), second most distant of the four and the largest satellite in the solar system, has heavily cratered regions, tens of miles across, that are surrounded by younger, grooved terrain. Callisto (diameter: 3,000 mi/4,806 km), the most distant and the least active geologically of the four, has a heavily cratered surface. Themisto (diameter: 5 mi/8 km) orbits Jupiter midway between the Galilean and next main group of satellites, the Himalias. The Himalia group consists of five tightly clustered satellites with orbits outside that of Callisto— Leda (diameter: 6 mi/10 km), Himalia (diameter: 106 mi/170 km), Lysithea (diameter: 15 mi/24 km), Elara (diameter: 50 mi/80 km), and S/2000 J11 (diameter: 2.5 mi/4 km). These 14 inner satellites are regular, that is, their orbits are relatively circular, near equatorial, and prograde, i.e., moving in the same orbital direction as the planet. Almost all of the remainder are irregular in that their orbits are large, elliptical, inclined to that of the planet, and usually retrograde, i.e., motion opposite to that of the planet's rotation. (Jupiter's irregular satellites are distinguished from the regular by the spelling of their names, which all end in the letter "e" .)

Situated between the Himalia and Ananke groups is Carpo (diameter: 2 mi/3 km), which like Thermisto doesn't seem to fit into any of the main groups. The Ananke group comprises 17 satellites, which share similar orbits and range from 1.2 to 2.5 mi (2-4 km) in diameter except for two: S/2003 J12, Euporie, Orthosie, Euanthe, Thyone, Mneme, Harpalyke, Hermippe, Praxidike (diameter: 4.5 mi/7 km), Thelexinoe, Iocaste, Ananke (diameter: 12.5 mi/20 km), S/2003 J16, S/2003 J3, S/2003 J18, Helike, and S/2003 J15.

Like the Ananke group, the Carme group is remarkably homogeneous. It comprises 17 satellites, which share similar orbits and, except for one, range from 1.2 to 3 mi (2-5 km) in diameter: Arche, Pasithee, Chaldene, Kale, Isonoe, Aitne, Erinome, Taygete, Carme (diameter: 28 mi/46 km), Kalyke, Eukelade, Kallichore, S/2003 J17, S/2003 J10, S/2003 J9, S/2003 J5, and S/2003 J19. The most distant of the groups from the planet is the Pasiphae, which comprises 14 widely dispersed satellites that, except for two, range from 1.2 to 4.5 mi (2-7 km) in diameter: S/2000 J12, Eurydome, Autonoe, Sponde, Pasiphae (diameter: 36 mi/58 km), Megaclite, Sinope (diameter: 23 mi/38 km), Hegemone, Aode, Callirrhoe, Cyllene, S/2000 J23, S/2000 J4, and S/2000 J14. The odd orbits of the irregular satellites indicate that they were captured after Jupiter's formation. Because they are small, irregularly shaped, and clustered into groups, it is believed that they originated as parts of a larger body that either shattered due to Jupiter's enormous gravity or broke apart in a collision with another body.

Jupiter has three rings — Halo, Main, and Gossamer —similar to those of Saturn but much smaller and fainter. An intense radiation belt lies between the rings and Jupiter's uppermost atmospheric layers.

Jupiter

Jupiter, the fifth planet from the Sun, is the largest and most massive planet in our solar system. It is 1,300 times larger than Earth, with more than 300 times the mass of Earth and 2.5 times the mass of all the other planets combined. It has a diameter over 88,000 miles (142,000 kilometers), more than eleven times Earth's diameter of 7,900 miles (12,700 kilometers). Lying about 480 million miles (770 million kilometers) from the Sun, Jupiter takes almost 12 years to complete one revolution.

With its 28 moons, Jupiter is considered a mini-solar system of its own. Before the twenty-first century, astronomers believed Jupiter had only 16 moons. But a rash of discoveries soon put the total at 28. The newly discovered satellites are highly different from Jupiter's more well-known moons. They are much smaller, with estimated diameters ranging from 1.8 to 5 miles (3 to 8 kilometers). Also, they have large and eccentric orbits. Some go around Jupiter in a clockwise direction, while others

orbit counter-clockwise. Astronomers speculate that Jupiter, while it was still young, captured the newly discovered moons from a group of small icy and rocky objects that orbit the Sun.

Jupiter is often the brightest object in the sky after the Sun and Venus. For some unknown reasons, it reflects light that is twice as intense as the sunlight that strikes it.

Jupiter has rings that are composed of small particles. Saturn, Uranus, and Neptune also have ring systems. It was only in late 1998 that

Dr. Joseph Burns, astronomy professor at Cornell University, and a team of researchers figured out how Jupiter's rings are formed. After studying photos taken by the unmanned spacecraft Galileo, astronomers announced that Jupiter's rings are formed when cosmic debris (such as asteroids or particles of comets) are pulled and smashed into Jupiter's moons by the planet's powerful magnetic field. The resulting collision produces dust clouds that become the rings around the planet.

Through a telescope, Jupiter appears as a globe of colorful swirling bands. These bands may be a result of the planet's fast rotation. One day on Jupiter lasts only 10 hours (compared to a rotational period of 24 hours on Earth).

Jupiter's most outstanding feature is its Great Red Spot. The spot is actually a swirling, windy storm measuring 16,000 miles (25,700 kilometers) long and 8,700 miles (14,000 kilometers) wide, an area large enough to cover two Earths. The spot may get its red color from sulfur or phosphorus, but no one is sure. Beneath it lie three white oval areas. Each is a storm about the size of Mars.

The planet's origin

One theory about Jupiter's origin is that the planet is made of the original gas and dust that came together to form the Sun and planets. Since it so far from the Sun, its components may have undergone little or no change. A more recent theory, however, states that Jupiter was formed from ice and rock from comets, and that it grew by attracting other matter around it.

Astronomers have been observing Jupiter since the beginning of recorded time. In 1610, Italian astronomer Galileo Galilei (1564–1642) looked through his recently developed telescope and discovered the planet's four largest moons: Io, Europa, Ganymede, and Callisto.

Discoveries by the Galileo probe

In 1989, the 2.5-ton (2.3-metric ton) Galileo space probe was launched aboard the space shuttle Atlantis. On December 7, 1995, Galileo began orbiting Jupiter and dropped a mini-probe the size of an average backyard barbecue grill. The probe entered Jupiter's atmosphere at a speed of 106,000 miles (170,500 kilometers) per hour. Soon after, the probe released a parachute and floated down to the planet's hot surface. As it fell, intense winds blew it 300 miles (480 kilometers) horizontally. The probe spent 58 minutes taking extremely detailed pictures of Jupiter until its cameras stopped working at an altitude of about 100 miles (160 kilometers) below the top of the planet's cloud cover. Eight hours later, the probe was completely vaporized as temperatures reached 3,400°F (1,870°C).

What the probe discovered first was a belt of radiation 31,000 miles (49,900 kilometers) above Jupiter's clouds, containing the strongest radio waves in the solar system. It next encountered Jupiter's swirling clouds and found that they contain water, helium, hydrogen, carbon, sulfur, and neon, but in much smaller quantities than expected. It also found gaseous krypton and xenon, but in greater amounts than previously estimated.

Scientists had predicted the probe would encounter three or four dense cloud layers of ammonia, hydrogen, sulfide, and water, but instead it found only thin, hazy clouds. The probe detected only faint signs of lightning at least 600 miles (965 kilometers) away, far less than expected. It also discovered that lightning on Jupiter occurs only one-tenth as often as it does on Earth. Perhaps the biggest surprise uncovered by the probe was the lack of water on the planet.

The probe did not survive long enough to gather information on Jupiter's core. Astronomers believe the planet has a rocky core made of material similar to that of Earth's core. The temperature of the core may be as hot as 18,000°F (9,820°C), with pressures two million times those

at Earth's surface. Scientists believe a layer of compressed hydrogen surrounds the core. Hydrogen in this layer may act like a metal and may be the cause of Jupiter's intense magnetic field (five times greater than the Sun's).

At the beginning of 2001, Galileo was still making valuable scientific observations about the planet and its moons, more than three years after its original two-year mission in orbit around Jupiter. The craft had already received three times the cumulative radiation exposure it was designed to withstand.

Comet Shoemaker-Levy 9 collides with Jupiter

In early 1993, Eugene Shoemaker (1928–1997), Carolyn Shoemaker (1948– ), and David Levy discovered a comet moving across the night sky. They were surprised at its appearance, since it seemed elongated compared to other comets they had seen. Further observations showed that the comet consisted of a large number of fragments, apparently torn apart during a close encounter with Jupiter during a previous orbit. Calculations showed that this "string of pearls" would collide with Jupiter in July 1994.

A global effort was mounted to observe the impacts with nearly all ground-based and space-based telescopes available. Although astronomers could not predict what effect the collisions would have on Jupiter, or even whether they would be visible, the results turned out to be spectacular. Observatories around the world and satellite telescopes such as the Hubble Space Telescope observed the impacts and their effects. Galileo, en route to Jupiter at the time, provided astronomers with a frontrow seat of the event. Even relatively small amateur telescopes were able to see some of the larger impact sites. Dark regions were visible in the atmosphere for months.

The data collected from the impact event will help scientists to understand the atmosphere of Jupiter, since the collisions dredged up material from parts of the atmosphere that are normally hidden. The wealth of information provided by Galileo, added to the Shoemaker-Levy impact data, is giving astronomers their best understanding yet of the biggest planet in our solar system.

[See also Comet; Solar system; Space probe ]

Jupiter (symbol ♃) The fifth planet from the Sun, and the largest planet in the Solar System, with a mass two and a half times greater than all the other planets combined. Its maximum opposition magnitude is −2.9, making it normally the second-brightest planet after Venus. Jupiter is distinctly ellipsoidal in shape (equatorial diameter 142 984 km, polar diameter 133 708 km). The rotation period of the visible surface is about 9 h 50 m in equatorial regions and about 9 h 56 m for the rest of the planet (see Systems I and II). The rotation of the solid surface, derived from radio observations, is thought to be 9 h 55 m 29s, known as System III.

Jupiter has a thick atmosphere composed of about 90 % hydrogen and 10 % helium (molecular percentages), plus traces of methane, ammonia, water, ethane, ethyne, phosphine, carbon monoxide, and germanium tetrahydride. Near the top of the atmosphere the temperature is around −143°C. Internally, Jupiter is thought to have an iron-rich rocky and perhaps icy core about 10 times the mass of the Earth. The pressure at the centre is thought to be about 10⁸bar. Surrounding this is a layer of dense hydrogen and liquid helium. Nearly 20 000 km below the surface the pressure reaches 3 million bar. Under these pressures the hydrogen begins to behave like a liquid metal, with convection currents that are probably responsible for Jupiter's strong magnetic field. The metallic hydrogen layer, about 50 000 km thick, is surrounded by a layer of normal molecular liquid hydrogen, which gradually merges into gaseous hydrogen near the surface. Giant aurorae and electrical storms occur in the planet's turbulent atmosphere. Jupiter's centre is estimated to be very hot, about 20 000 K. This internal heat is left over from the kinetic energy of impacts during accretion, and from the conversion of gravitational potential energy into heat when the core formed.

jupiter

Jupiter Fifth major planet from the Sun and the largest of the giant planets. It is one of the brightest objects in the sky. Through a telescope, Jupiter's yellowish elliptical disk is seen to be crossed by brownish-red bands, known as belts and zones. The most distinctive feature is the Great Red Spot (GRS), first observed (1664) by Robert Hooke. Jupiter's rapid rotation and turbulent atmosphere prouduces spots, streaks, and bands. Eddies give rise to the spots, which are cyclones or (like the GRS) anticyclones. Hydrogen accounts for nearly 90% of Jupiter's atmosphere and helium for most of the rest. The pressure at the cloud tops is c.0.5 bar. At 1000km (600mi) below the cloud tops there is an ocean of liquid molecular hydrogen. At a depth of 20,000–25,000km (12,500–15,000mi), under a pressure of 3 million bars, the hydrogen becomes so compressed that it behaves as a metal. At the centre of Jupiter, there is probably a massive iron-silicate core surrounded by an ice mantle. The core temperature is estimated to be 30,000K. The deep, metallic hydrogen ‘mantle’ gives Jupiter a powerful magnetic field. It traps a large quantity of plasma (charged particles); high-energy plasma funnels into the radiation belts. Jupiter's magnetosphere is huge, several times the size of the Sun, and is the source of the planet's powerful radio emissions. Jupiter has 16 known satellites, the four major ones being the Galilean satellites. Knowledge of the planet owes much to visits by space probes: Pioneers 10 and 11, Voyagers 1 and 2, Ulysses, and Galileo.

http://lpl.arizona.edu/nineplanets/nineplanets/jupiter.html; http://wr.usgs.gov

Jupiter, also Jove. The chief patriarch of the Roman pantheon, god of sky and thunderbolts, protector of oaths, was widely worshipped in Romano-Celtic religion, often with local epithets. Under the process of interpretatio celtica (see GAUL), the native populations of Roman colonies adapted the imperial god to local religious needs. Not surprisingly, classical commentators described Jupiter as ranking lower in native esteem than Gaulish Mercury, Gaulish Apollo, and Gaulish Mars, Celtic gods given Roman names under interpretatio romana. Evidence from non-Roman sources implies that the Continental Celtic Taranis most resembles Jupiter, as does Bussumarus, although it is not clear that either is identical with ‘Gaulish Jupiter’. About 150 columns were erected to honour Jupiter, from eastern Gaul through the Moselle and Rhine valleys. The upper figure is usually seen trampling a serpent-like anthropomorphic monster. Jupiter's placement here may be to put him as high as possible into the sky, his realm, or to link him with trees. Contemporary commentators give little heed to Sir John Rhŷs's (1886) assertation that Nodons, Conchobar mac Nessa, Conaire Mór, and Cormac mac Airt could be related to Zeus, Jupiter's Greek counterpart.

Jupiter in Roman mythology, the chief god of the Roman state religion, giver of victory, originally a sky god associated with thunder and lightning. His wife was Juno. Also called Jove. His Greek equivalent is Zeus. The name is Latin, from Jovis pater, literally ‘Father Jove’.

In astronomy, Jupiter is the name given to the largest planet in the solar system, a gas giant which is the fifth in order from the sun and one of the brightest objects in the night sky.
Jupiter Ammon a deity worshipped in the Egyptian western desert, where the cult of the Egyptian god Amun was linked with Jupiter.

Jupiter The fifth and largest planet in the solar system, distant 5.203 AU from the Sun. It has a radius of 71 900 km, and a mass 318 times and a volume 1403 times that of the Earth. Its density is 1310 kg/m³ and it is comprised mainly of hydrogen and helium. The atmosphere is 0.9H-0.1 He (with traces of H₂O, CH₄, and NH₃) which grades down into a liquid shell, overlying a zone of metallic hydrogen. In the centre is a small rock-ice core of about ten Earth masses. Jupiter has at least 16 satellites, including the four Galilean satellites.

Jupiter in Roman religion and mythology, the supreme god, also called Jove. Originally a sky deity associated with rain and agriculture, he developed into the great father god, prime protector of the state, concerned, like the Greek Zeus (with whom he is identified), with all aspects of life. At his temple on the Capitol, triumphant generals honored him with their spoils and magistrates paid homage to him with sacrifices. Jupiter was the son of Saturn and Ops and the brother and husband of Juno .

Jupiter The chief god in the Roman pantheon, equivalent to the Greek Zeus, to whom many temples were dedicated in the Roman Empire. At Lystra, after the healing of a cripple, a crowd acclaimed Barnabas as Jupiter (Zeus) and Paul as Mercury (Hermes); the apostles deprecated this (Acts 14: 15).

Jupiter was associated with storms and thunder, but was especially venerated as the protector of the Roman people.

Ju·pi·ter / ˈjoōpitər/ 1. Roman Mythol. the chief god of the Roman state religion, originally a sky god associated with thunder and lightning. His wife was Juno. Also called Jove. Greek equivalent Zeus. 2. Astron. the largest planet in the solar system, a gas giant that is the fifth in order from the sun and one of the brightest objects in the night sky.

Jupiter an intermediate range ballistic missile originally put on an accelerated development schedule after the Soviet Union completed ICBM tests in 1957. It was later scrapped because of problems finding sites for the missiles in other countries.

Jupiter supreme deity of the ancient Romans XIII, (in earliest use Iubiter); largest of the planets XIII; (alch.) †tin XIV; †(her., in blazoning by the names of heavenly bodies) azure XVI. — L.; see JOVIAL.

Jupiter King of the Roman gods, identified with the Greek god Zeus. He could take on various forms: the light-bringer (Lucetius), god of lightning and thunderbolts (Fulgur), and god of rain (Jupiter Elicius).

Jupiter •bitter, committer, critter, embitter, emitter, fitter, flitter, fritter, glitter, gritter, hitter, jitter, knitter, litter, permitter, pitta, quitter, remitter, sitter, skitter, slitter, spitter, splitter, submitter, titter, transmitter, twitter, witter •drifter, grifter, lifter, shifter, sifter, snifter, uplifter •constrictor, contradictor, depicter, dicta, evictor, inflicter, predictor, victor •filter, kilter, philtre (US philter), quilter, tilter •Jacinta, midwinter, Minter, Pinta, Pinter, printer, splinter, sprinter, tinter, winter •sphincter •assister, ballista, bistre (US bister), blister, enlister, glister, lister, mister, resistor, Sandinista, sister, transistor, tryster, twister, vista •trickster •minster, spinster •hipster, quipster, tipster •cohabiter • arbiter • presbyter •exhibitor, inhibitor, prohibiter •Manchester • Chichester • Silchester •Rochester • Colchester •creditor, editor, subeditor •auditor • Perdita • taffeta • shopfitter •forfeiter • outfitter • counterfeiter •register • marketer •cricketer, picketer •Alistair • weightlifter • filleter •fillister • shoplifter •diameter, heptameter, hexameter, parameter, pentameter, tetrameter •Axminster • Westminster •limiter, perimeter, scimitar, velocimeter •accelerometer, anemometer, barometer, gasometer, geometer, manometer, micrometer, milometer, olfactometer, optometer, pedometer, photometer, pyrometer, speedometer, swingometer, tachometer, thermometer •Kidderminster • janitor •banister, canister •primogenitor, progenitor, senator •administer, maladminister, minister, sinister •monitor • per capita • carpenter •spanakopita • Jupiter • trumpeter •character • barrister • ferreter •teleprinter •chorister, forester •interpreter, misinterpreter •capacitor • ancestor • Exeter •stepsister •elicitor, solicitor •babysitter • house-sitter • bullshitter •competitor • catheter • harvester •riveter • banqueter • non sequitur •loquitur •inquisitor, visitor •compositor, expositor