FREE ESSAY ON JUPITER AND IT'S MOONS

JUPITER AND IT'S MOONS

Jupiter
And It's Moons
Jupiter, the largest of the Jovian planets, reigns supreme throughout the solar 
system. Named after the Roman god Jove, the ruler of Olympus; Jupiter is the fifth 
planet from the sun and is also the largest planet in the Earth's solar system. It is 318

times moremassive than Earth and is two thirds of the planetary mass in the solar system.

Jupiter's surface, unlike earth, is gaseous and 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's interior but with a far lower temperature.(Columbia) However, it is

still unknown for certain, but Jupiter is believed to have a core of liquid metallic 
hydrogen. This exotic element can only be achieved at a pressure greater than 4 million 
bars. Jupiter radiates more energy in space than it receives from the sun. 
Jupiter's orbit lies beyond the asteroid belt at a mean distance of c.483 million mi 
(773 million km) from the sun; its period of revolution is 11.86 years. (Seeds) 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 88,679 mi (142,800 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 allother planets combined. (Columbia)
A measurement of the diameter of Jupiter determined the planet's polar flattening. 
The flattening of Jupiter was revealed by Pioneer to be slightly greater than 
that derived from the best Earth-based measurements. The diameter of the planet was 
measured at a pressure of 800 mbar near the cloud tops (a bar is roughly equal to the 
pressure of 1 atm of Earth). Its polar diameter is 133,540 km (82,980 miles) and its 
equatorial diameter is142, 796 kilometers (88,732 miles). (Seeds) These values were 
established by the timing of the occultation of the spacecraft by Jupiter. Thus, Jupiter
is 
nearly 20 times more fattened than Earth, principally because of its non-solid state and
its 
higher rate of rotation. The average density of Jupiter, calculated from its mass and 
volume, was confirmed as 1.33 gm/cm^3 (the density of water is 1).
The atmosphere of Jupiter is composed mainly of hydrogen, helium, methane, and 
ammonia. It appears the atmosphere is divided into a number of light and dark bands 
parallel to its equator and shows a range of complex features, including an ongoing storm

called the Great Red Spot, located in its southern hemisphere and measuring 16,150 mi 
long by 8,700 mi wide (26,000 by 14,000 km). (Columbia)
This Great Red Spot is still present in Jupiter's atmosphere, more than 300 years 
later. It is now 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 a 
counterclockwise direction in the southern hemisphere, showing that it is a high-pressure

system. Winds inside this Jovian storm reach speeds of about 270 mph. The Red Spot is 
the largest known storm in the Solar System. With a diameter of 15,400 miles, it is 
almost twice the size of the entire Earth and one-sixth the diameter of Jupiter itself. 
(Fimmel) The Great Red Spot was first detected by Robert Hooke in 1664. 
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. 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%. (Columbia)
The temperature of Jupiter 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 non-thermal radio emission; in the 15-m range it is the

strongest radio source in 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 ring appeared to be a 
single ring, but Galileo imagery provided the unexpected discovery that Gossamer is 
really two rings. One ring is embedded within the other. The rings are very tenuous and 
are composed of dust particles kicked up as 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 from about 
92,000 kilometers (57,000 miles) to about 122,500 kilometers (76,000 miles) from 
Jupiter's center. It is formed as fine particles of dust from the main 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 to about 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 two faint Gossamer rings are fairly uniform in

nature. The innermost Amalthea Gossamer ring extends from the orbit of Adrastea out to 
the orbit of Amalthea at 181,000 kilometers (112,000 miles) from Jupiter's center. 
(Hamilton)
The fainter Thebe Gossamer ring extends from Amalthea's orbit out to about 
Thebe's orbit at 221,000 kilometers (136,000 miles). 
Jupiter's rings and moons exist within an intense radiation belt of electrons and 
ions trapped in the planet's magnetic field. These particles and fields comprise the 
Jovian magnetosphere 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 at least as
far 
as Saturn's orbit - a distance of 750 million kilometers (466 million miles). (Seeds)
Jupiter has a huge magnetic field, much stronger than Earth's called the 
magnetosphere. The magnetosphere is not a true sense a perfect sphere. It is highly 
flattened due to the rapid rotation of Jupiter. This magnetic field causes phenomenon 
such as strong lightening and even an aurora similar to earth's aurora borealis. Plasma 
flows in the dayside outer magnetosphere; the plasma rotates with the planet every 10 
hours. (Hamilton)
Jupiter, unlike earth, has three distinct weather-producing zones or a troposphere. 
They are believed to contain Ammonia ice, ammonium hydrosulfide, and water and ice. 
In the apparent or uppermost atmosphere, ammonia ice crystals thrive in a temperature 
of about 150 degrees Kelvin. (A.U.R.A.) Most astronomers theorize that the next level 
of the atmosphere is primarily made up of Ammonium hydrosulfide crystals in a 
temperature of 200 degrees Kelvin. 
It is also theorized that the third and final level before the liquid metallic 
hydrogen is a layer of liquid ammonia and water droplets. Jupiter's atmosphere is also 
plagued by high velocity winds that move in wide bands. These winds blow in opposite 
directions along the latitude of the planet. Because of chemical reactions and
differences, 
they can be seen wrapping around Jupiter in colorful bands. The light colored bands are 
called zones and the dark colored bands are called belts. It is not known whether the
belts 
and zones are permanent; they have not changed in eighty years of observance. One 
theory is that the jet stream at the belt-zone boundaries are linked to circulation
patterns 
deep in the liquid interior (Seeds).
At least sixteen natural satellites are known to orbit Jupiter. Twelve of Jupiter's moons

are relatively small and seem to have been more likely captured than to have been formed

in orbit around Jupiter. They are conveniently divided into three groups. The four
largest-
-Io, Europa, Ganymede, and Callisto--were discovered by Galileo in 1610, shortly after 
he invented the telescope, and is known as the Galilean satellites. 
These large moons are believed to have accreted as part of the process by which 
Jupiter itself formed. (Fimmel) Accretion is the accumulation of dust and gas into 
larger bodies. (Astronomy) Ganymede is the largest satellite in the solar system; with a

diameter of 3,268 mi (5,262 km), it is larger than the planet Mercury. In 1979 Io was 
observed by Voyager I and II and was found to have several active volcanoes actually in 
eruption during 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 of the Galilean satellites. When the Galileo 
spacecraft flew by Io in December 1995; it discovered that Io has an iron inner core. A 
high-altitude ionosphere was also revealed by the Galileo flyby. In 1979, the Voyager 
spacecraft flew through the Jovian system, and one of the most exciting discoveries made

by the Voyager spacecraft was the presence of active erupting volcanoes on Io. 
(Helicon).
It was discovered that Io was the most volcanically 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 tidal tug-of-war between Jupiter, Europa and Ganymede.(Helicon). The 
largest volcano on Io is named Pele. Pele was the first volcano discovered on Io and it 
was actively erupting with a plume an astonishing 300 km high at the time of its 
discovery. The Voyager spacecraft observed eleven active volcanoes during their flyby. 
Hundreds of volcanic calderas have also been observed. (Fimmel).
There are no impact craters on Io. Therefore, the surface of Io is believed to be 
younger than a millions years old, and is continually being resurfaced by volcanic 
activity. Also, the surface is very colorful, covered with red, yellow, white and orange

black markings. The surface composition on Io consists largely of sulfur with deposits of

frozen sulfur dioxide. The surface on Io is mostly flat plains rising no more than 1km. 
Mountain ranges up to 9 km high have also been observed. A torus of sodium gas along 
with sulfur ions is spread out over Io's orbit. This torus is so large that it has been 
observed from Earth. (Io;Helicon)
Europa is a strange looking moon of Jupiter with a large number of intersecting 
features. It is unlike Callisto and Ganymede with their heavily cratered crusts. Europa 
has almost a complete absence of craters as well as almost no vertical relief. 
(Europa;Helicon). As one scientist put it, the features might have been painted on with a

felt marker (Seeds). There is a possibility that Europa may be internally active due to 
tidal heating at a level one-tenth or less that of Io. Models of Europa'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 visible markings on Europa could be a result of global 
expansion where the crust could have fractured, filled with water and froze. 
(Europa;Helicon).
Ganymede is the largest moon of the planet Jupiter, and the largest moon in the 
Solar System, 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. Molecular oxygen 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 photographed 
Ganymede at a distance of 7,448 km/4,628 mi. The resulting images were 17 times 
clearer than those taken by Voyager 2 in 1979, and show the surface to be extensively 
cratered and ridged, probably as a result of forces similar to those that create
mountains 
on Earth. Galileo also detected molecules containing both carbon and nitrogen on the 
surface March 1997. Their presence may indicate that Ganymede harbored life at some 
time (Hamilton).
Callisto is the eighth of Jupiter's known satellites and the second largest. It is the 
outermost of the Galilean moons and was discovered by Galileo and Marius in 1610. 
Unlike Ganymede, Callisto seems to have little internal structure; However, there are 
signs from recent Galileo data that the interior materials have settled partially, with
the 
percentage of rock increasing toward the center. Callisto is about 40% ice and 60% 
rock/iron  (Callisto;Helicon). Callisto's surface is covered entirely with craters. The 
surface is very old, like the highlands of the Moon and Mars. Callisto has the oldest, 
most cratered surface of any body yet observed in the solar system; having undergone 
little change other than the occasional impact for 4 billion years (Callisto;Helicon).
The largest craters are surrounded by a series of concentric rings that look like 
huge cracks but which have been smoothed out by eons of slow movement of the ice. 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 massive impact  
(Callisto;Helicon).
In terms of the mass of Earth's Moon, the masses of the Galilean satellites in 
order of distance from Jupiter were found to be: Io, 1.21; Europa, 0.65; Ganymede, 2.02;

and Callisto, 1.46. The mass of Io was 23% greater than that estimated before the 
Pioneer odyssey. The density of the satellites decreases with increasing distance from 
Jupiter and was 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 outer satellites, 
because of their low density, could consist largely of water and ice. All four satellites

were found to have average daylight surface temperatures of about-140 C (-220 F)  
(Columbia).
A second group is comprised 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 group 
consists 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 to 16 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 have direct 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 visible in a dark sky). The four Galilean moons 
are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a

small astronomical telescope. 
Jupiter is very gradually slowing down due to the tidal drag produced by the 
Galilean satellites. How will this effect it and its moons? We currently know that the 
same tidal forces that are slowing Jupiter down are changing the orbits of the moons,
very 
slowly forcing them farther from Jupiter. As additional data 
is gathered and technology enables a new fronitier, only then will we know the fate of 
Jupiter. Until then we can merely speculate it's final life as a Jovian planet. 
Bibliography
Bibliography
The Columbia Encyclopedia, Fifth Edition. Copyright ?1993, Columbia University Press.
Licensed from Lernout & Hauspie Speech Products USA, Inc. 
Pioneer: First to Jupiter, Saturn, and Beyond: Chapter 6A Results At The New Frontier;
Fimmel, Richard O.; Van Allen, James; Burgess, Eric; 09-01-1990
Ganymede; ( The Hutchinson Dictionary of Science ) ; 01-01-1998, Helicon Publishing Ltd.
1998. 
Io ; ( The Hutchinson Dictionary of Science ) ; 01-01-1998, Helicon Publishing Ltd. 1998.

Callisto; ( The Hutchinson Dictionary of Science ) ; 01-01-1998, Helicon Publishing Ltd.
1998. 
Europa; ( The Hutchinson 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 Association of Universities for Research in Astronomy, Inc. 
Author not available, Astronomy: Common Terms in Astronomy. , The New York Public
Library Science Desk Reference, 01-01-1995.