Jupiter, the largest of the Jovian planets, reigns supreme throughout the solarsystem. Named after the Roman god Jove, the ruler of Olympus; “Jupiter isthe fifth planet from the sun and is also the largest planet in the Earth’ssolar system. It is 318 times moremassive than Earth and is two thirds of theplanetary mass in the solar system. Jupiter’s surface, unlike earth, is gaseousand not a solid. It is about 90% hydrogen and 10% helium with traces of methane,ammonia, water and rock.
Jupiter’s interior is very similar to the Sun’sinterior but with a far lower temperature. “(Columbia) However, it is stillunknown for certain, but Jupiter is believed to have a core of liquid metallichydrogen. This exotic element can only be achieved at a pressure greater than 4million bars. Jupiter radiates more energy in space than it receives from thesun.
“Jupiter’s orbit lies beyond the asteroid belt at a mean distance ofc. 483 million mi (773 million km) from the sun; its period of revolution is11. 86 years. ” (Seeds) In order from the sun it is the first of the Jovianplanets (Jupiter, Saturn, Uranus, and Neptune), very large, massive planets ofrelatively low density, having rapid rotation and a thick, opaque atmosphere. “Jupiter has a diameter of 88,679 mi (142,800 km), more than 11 times thatof the earth.
Its mass is 318 times that of the earth and about 2 1/2 times themass of allother planets combined. ” (Columbia) A measurement of thediameter of Jupiter determined the planet’s polar flattening. The flattening ofJupiter was revealed by Pioneer to be slightly greater than that derived fromthe best Earth-based measurements. “The diameter of the planet was measuredat a pressure of 800 mbar near the cloud tops (a bar is roughly equal to thepressure of 1 atm of Earth). Its polar diameter is 133,540 km (82,980 miles) andits equatorial diameter is142, 796 kilometers (88,732 miles). ” (Seeds)These values were established by the timing of the occultation of the spacecraftby Jupiter.
Thus, Jupiter is nearly 20 times more fattened than Earth,principally because of its non-solid state and its higher rate of rotation. Theaverage density of Jupiter, calculated from its mass and volume, was confirmedas 1. 33 gm/cm^3 (the density of water is 1). The atmosphere of Jupiter iscomposed mainly of hydrogen, helium, methane, and ammonia. “It appears theatmosphere is divided into a number of light and dark bands parallel to itsequator and shows a range of complex features, including an ongoing storm calledthe Great Red Spot, located in its southern hemisphere and measuring 16,150 milong by 8,700 mi wide (26,000 by 14,000 km).
” (Columbia) This Great RedSpot is still present in Jupiter’s atmosphere, more than 300 years later. It isnow known that it is a vast storm, spinning like a cyclone. Unlike a low-pressure hurricane in the Caribbean Sea, however, the Red Spot rotates in acounterclockwise direction in the southern hemisphere, showing that it is ahigh-pressure system. “Winds inside this Jovian storm reach speeds of about270 mph.
The Red Spot is the largest known storm in the Solar System. With adiameter of 15,400 miles, it is almost twice the size of the entire Earth andone-sixth the diameter of Jupiter itself. ” (Fimmel) The Great Red Spot wasfirst detected by Robert Hooke in 1664. Jupiter has no solid rock surface. Onetheory pictures a gradual transition from the outer ammonia clouds to a thicklayer of frozen gases and finally to a liquid or solid hydrogen mantle. “The Spot and other markings of the atmosphere also provide evidence forJupiter’s rapid rotation, which has a period of about 9 hr 55 min.
This rotationcauses a polar flattening of over 6%. ” (Columbia) The temperature ofJupiter ranges from about -190? F (-124?C) for the visible surface of theatmosphere, to 9? F (-13? C) at lower cloud levels; localized regions reach ashigh as 40? F (4? C) at still lower cloud levels near the equator. Jupiterradiates 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 toa slow contraction of the planet.
Jupiter is also characterized by intensenon-thermal radio emission; in the 15-m range it is the strongest radio sourcein the sky. Jupiter has a simple ring system that is composed of an inner halo,a main ring and a Gossamer ring. To the Voyager spacecraft, the Gossamer ringappeared to be a single ring, but Galileo imagery provided the unexpecteddiscovery that Gossamer is really two rings. One ring is embedded within theother. The rings are very tenuous and are composed of dust particles kicked upas interplanetary meteoroids smash into Jupiter’s four small inner moons Metis,Adrastea, Thebe, and Amalthea.
Many of the particles are microscopic in size. “The innermost halo ring is toroidal in shape and extends radially fromabout 92,000 kilometers (57,000 miles) to about 122,500 kilometers (76,000miles) from Jupiter’s center. It is formed as fine particles of dust from themain ring’s inner boundary ‘bloom’ outward as they fall toward the planet. “(A. U. R.
A. ) The main and brightest ring extends from the halo boundary out toabout 128,940 kilometers (80,000 miles) or just inside the orbit of Adrastea. Close to the orbit of Metis, the main ring’s brightness decreases. “The twofaint Gossamer rings are fairly uniform in nature.
The innermost AmaltheaGossamer ring extends from the orbit of Adrastea out to the orbit of Amalthea at181,000 kilometers (112,000 miles) from Jupiter’s center. ” (Hamilton) Thefainter Thebe Gossamer ring extends from Amalthea’s orbit out to about Thebe’sorbit at 221,000 kilometers (136,000 miles). Jupiter’s rings and moons existwithin an intense radiation belt of electrons and ions trapped in the planet’smagnetic field. “These particles and fields comprise the Jovianmagnetosphere or magnetic environment, which extends 3 to 7 million kilometers(1. 9 to 4.
3 million miles) toward the Sun, and stretches in a windsock shape atleast as far as Saturn’s orbit – a distance of 750 million kilometers (466million miles). ” (Seeds) Jupiter has a huge magnetic field, much strongerthan Earth’s called the magnetosphere. The magnetosphere is not a true sense aperfect sphere. It is highly flattened due to the rapid rotation of Jupiter.
This magnetic field causes phenomenon such as strong lightening and even anaurora similar to earth’s aurora borealis. “Plasma flows in the daysideouter magnetosphere; the plasma rotates with the planet every 10 hours. “(Hamilton) Jupiter, unlike earth, has three distinct weather-producing zones ora troposphere. They are believed to contain Ammonia ice, ammonium hydrosulfide,and water and ice. “In the apparent or uppermost atmosphere, ammonia icecrystals thrive in a temperature of about 150 degrees Kelvin.
” (A. U. R. A.
)Most astronomers theorize that the next level of the atmosphere is primarilymade up of Ammonium hydrosulfide crystals in a temperature of 200 degreesKelvin. It is also theorized that the third and final level before the liquidmetallic hydrogen is a layer of liquid ammonia and water droplets. Jupiter’satmosphere is also plagued by high velocity winds that move in wide bands. Thesewinds blow in opposite directions along the latitude of the planet. Because ofchemical reactions and differences, they can be seen wrapping around Jupiter incolorful bands. The light colored bands are called zones and the dark coloredbands are called belts.
It is not known whether the belts and zones arepermanent; they have not changed in eighty years of observance. “One theoryis that the jet stream at the belt-zone boundaries are linked to circulationpatterns deep in the liquid interior” (Seeds). At least sixteen naturalsatellites are known to orbit Jupiter. Twelve of Jupiter’s moons are relativelysmall and seem to have been more likely captured than to have been formed inorbit around Jupiter. They are conveniently divided into three groups.
The fourlargest- -Io, Europa, Ganymede, and Callisto–were discovered by Galileo in1610, shortly after he invented the telescope, and is known as the Galileansatellites. “These large moons are believed to have accreted as part of theprocess by which Jupiter itself formed. ” (Fimmel) “Accretion is theaccumulation of dust and gas into larger bodies. ” (Astronomy) Ganymede isthe largest satellite in the solar system; with a diameter of 3,268 mi (5,262km), it is larger than the planet Mercury.
In 1979 Io was observed by Voyager Iand II and was found to have several active volcanoes actually in eruptionduring the spacecraft flyby. Io is the innermost of the Galilean satellites. Io’s size and density is very similar to our own Moon, and it the most dense ofthe Galilean satellites. “When the Galileo spacecraft flew by Io inDecember 1995; it discovered that Io has an iron inner core. A high-altitudeionosphere was also revealed by the Galileo flyby. In 1979, the Voyagerspacecraft flew through the Jovian system, and one of the most excitingdiscoveries made by the Voyager spacecraft was the presence of active eruptingvolcanoes on Io.
” (Helicon). It was discovered that Io was the mostvolcanically active planet in the solar system, even more active than the Earth. “The volcanism on Io is due to the internal heat generated by the tidaltug-of-war between Jupiter, Europa and Ganymede. “(Helicon). The largestvolcano on Io is named Pele. Pele was the first volcano discovered on Io and itwas actively erupting with a plume an astonishing 300 km high at the time of itsdiscovery.
The Voyager spacecraft observed eleven active volcanoes during theirflyby. “Hundreds of volcanic calderas have also been observed. ” (Fimmel). There are no impact craters on Io. Therefore, the surface of Io is believed tobe younger than a millions years old, and is continually being resurfaced byvolcanic activity.
Also, the surface is very colorful, covered with red, yellow,white and orange black markings. The surface composition on Io consists largelyof sulfur with deposits of frozen sulfur dioxide. The surface on Io is mostlyflat plains rising no more than 1km. Mountain ranges up to 9 km high have alsobeen observed. “A torus of sodium gas along with sulfur ions is spread outover Io’s orbit. This torus is so large that it has been observed fromEarth.
” (Io;Helicon) Europa is a strange looking moon of Jupiter with alarge number of intersecting features. It is unlike Callisto and Ganymede withtheir heavily cratered crusts. “Europa has almost a complete absence ofcraters as well as almost no vertical relief. ” (Europa;Helicon). As onescientist put it, the features “might have been painted on with a feltmarker” (Seeds). There is a possibility that Europa may be internallyactive due to tidal heating at a level one-tenth or less that of Io.
Models ofEuropa’s interior show that beneath a thin 5 km (3 miles) crust of water ice,Europa may have oceans as deep as 50 km (30 miles) or more. “The visiblemarkings on Europa could be a result of global expansion where the crust couldhave fractured, filled with water and froze. ” (Europa;Helicon). Ganymede isthe largest moon of the planet Jupiter, and the largest moon in the SolarSystem, 5,260 km/3,270 mi in diameter which is larger than the planet Mercury.
It orbits Jupiter every 7. 2 days at a distance of 1. 1 million km/700,000 mi. ” Its surface is a mixture of cratered and grooved terrain. Molecularoxygen was identified on Ganymede’s surface in 1994″ (Ganymede;Helicon).
“The space probe Galileo detected a magnetic field around Ganymede in 1996;this suggests it may have a molten core. ” (Hamilton). Galileo photographedGanymede at a distance of 7,448 km/4,628 mi. The resulting images were 17 timesclearer than those taken by Voyager 2 in 1979, and show the surface to beextensively cratered and ridged, probably as a result of forces similar to thosethat create mountains on Earth. “Galileo also detected molecules containingboth carbon and nitrogen on the surface March 1997.
Their presence may indicatethat Ganymede harbored life at some time” (Hamilton). Callisto is theeighth of Jupiter’s known satellites and the second largest. It is the outermostof the Galilean moons and was discovered by Galileo and Marius in 1610. UnlikeGanymede, Callisto seems to have little internal structure; However, there aresigns from recent Galileo data that the interior materials have settledpartially, with the percentage of rock increasing toward the center.
“Callistois about 40% ice and 60% rock/iron ” (Callisto;Helicon). Callisto’s surfaceis covered entirely with craters. The surface is very old, like the highlands ofthe Moon and Mars. “Callisto has the oldest, most cratered surface of anybody yet observed in the solar system; having undergone little change other thanthe occasional impact for 4 billion years” (Callisto;Helicon).
“Thelargest craters are surrounded by a series of concentric rings that look likehuge cracks but which have been smoothed out by eons of slow movement of theice. The largest of these has been named Valhalla (right). 4000 km in diameter,Valhalla is a dramatic example of a multi-ring basin, the result of a massiveimpact ” (Callisto;Helicon). “In terms of the mass of Earth’s Moon,the masses of the Galilean satellites in order of distance from Jupiter werefound to be: Io, 1.
21; Europa, 0. 65; Ganymede, 2. 02; and Callisto, 1. 46. Themass of Io was 23% greater than that estimated before the Pioneer odyssey. Thedensity of the satellites decreases with increasing distance from Jupiter andwas refined as a result of Pioneer’s observations.
Io’s density is 3. 52;Europa’s, 3. 28; Ganymede’s, 1. 95; and Callisto’s, 1. 63 gm/cm^3.
The outersatellites, because of their low density, could consist largely of water andice. All four satellites were found to have average daylight surfacetemperatures of about-140 C (-220 F) ” (Columbia). A second group iscomprised of the four innermost satellites–Metis, Adrastea, Amalthea, and Thebe. Discovered by E. E. Barnard in 1892, Amalthea has an oblong shape and is 168 mi(270 km) long.
Metis and Adrastea orbit close to Jupiter’s thin ring system;material ejected from these moons helps maintain the ring. The final groupconsists of the eight remaining satellites, none larger than c. 110 mi (180 km)in diameter. “Four of the outer eight satellites located from 14 million to16 million mi from Jupiter (22 million-26 million km), have retrograde motion,i. e. , motion opposite to that of the planet’s rotation.
The other four havedirect orbits. It is speculated that all eight might be captured asteroids”(Seeds). When it is in the nighttime sky, Jupiter is often the brightest”star” in the sky (it is second only to Venus, which is seldom visiblein a dark sky). The four Galilean moons are easily visible with binoculars; afew bands and the Great Red Spot can be seen with a small astronomicaltelescope.
Jupiter is very gradually slowing down due to the tidal drag producedby the Galilean satellites. How will this effect it and its moons? We currentlyknow that the same tidal forces that are slowing Jupiter down are changing theorbits of the moons, very slowly forcing them farther from Jupiter. Asadditional data is gathered and technology enables a new fronitier, only thenwill we know the fate of Jupiter. Until then we can merely speculate it’s finallife as a Jovian planet. BibliographyBibliography The Columbia Encyclopedia, Fifth Edition. Copyright ?1993,Columbia University Press.
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1998. Callisto; ( The Hutchinson Dictionaryof Science ) ; 01-01-1998, Helicon Publishing Ltd. 1998. Europa; ( TheHutchinson Dictionary of Science ) ; 01-01-1998, Helicon Publishing Ltd. 1998.
Seeds, Michael A. , Foundations of Astronomy; copyright 1994, Wadsworth Inc. Copyright ? 1997-1999 by Calvin J. Hamilton. Copyright ? 1998 The Associationof Universities for Research in Astronomy, Inc.
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