Jupiter General Information

INTRO: 
      Jupiter is the largest of all the planets in the solar system, 318 times more 
massive than Earth. Even though it is of such a great mass, its density is less than
twenty five percent of that of the Earth. These facts indicate that the chemical 
composition of this planet is similar to that of the sun, in which it consists 
mostly of hydrogen and helium. Jupiter's clouds have one lasting feature, the great 
red spot. This is caused by a spinning cloud that is large enough to encase an area 
as large as several earths. Jupiter was named after the king of the Roman gods, the 
lord of the sky. Jupiter revolves around the sun with a radius that is five times 
that of the earth. Due to this, it can be seen from our skies for most of the year. 
Each year it appears to shift about 30 degrees eastward which helps create a 12 
year cycle. Jupiter has no solid surface which leaves nothing to tie down its 
atmosphere. Thus, Jupiter exhibits differential rotation, meaning that its rotation 
rate is not the same from one location to another. Its equatorial zones rotate more 
rapidly than the polar regions. The central temperature of Jupiter is about 20,000 
degrees Kelvin, compared to 7000 degrees for earth and 15,000,000 degrees for the 
sun. 

       The coloration of Jupiter is a result of the interaction of sunlight to the 
atmosphere and the clouds. Different chemicals absorb different colors of light. 
Jupiter has two distinct features. One is the constantly changing atmospheric bands 
arranged parallel to the equator, and the other called the Great Red Spot. The 
cloud bands are visible in many different colors: yellows, blues, browns and reds. 
Scientists believe that chemical compounds in Jupiter's atmosphere create these 
different colors, but the chemistry is still not completely understood. The Great 
Red Spot is one of many features associated with Jupiter's weather. It seems to be 
an Earth-sized hurricane that has persisted for hundreds of years. 

     A remarkable finding of the 1979 Voyager mission was the discovery of a faint 
ring of matter encircling Jupiter at its equator. This ring lies roughly 31,000 
miles (50,000 km) above the top cloud layer of this planet and inside the orbit of 
the innermost moon. The outer edge of the ring is sharply defined, but only a few 
tens of kilometers thick. The dark particles that make up the ring may have been 
chipped off by meteorite impacts on two small moons that lie very close to the ring 
itself. 

     Not only is Jupiter the largest planet, it has four of the largest moons or 
satellites. These are Io, Europa, Ganymede, and Callisto. These are known as the 
Galilean satellites, after their discoverer, Galileo Galilei in 1610.

Discovering Jupiter:
     A Pioneer Mission to Jupiter was approved in 1969 by NASA. The goal was to fly 
two spacecraft by Jupiter, but soon it was seen that Saturn could be observed as 
well. Pioneer 10 was launched on March 2, 1972, and Pioneer 11 on April 3, 1973. 
These spacecraft swept across targeted areas but the instruments could not stay in 
one single place for a time exposure of any region because of their fixed rates of 
rotation. Images were obtained with a scanning photometer. This was able to be 
placed perpendicular to the spinning spacecraft. 23 images were transmitted to 
Earth by Pioneer 10 and 17 by Pioneer 11 in 24 hours. Although the images revealed 
little new information, new facts about temperature and pressure within the 
atmosphere was obtained by infrared detectors. Astronomers learned of the rich 
hydrogen atmosphere similar to our sun. 

      In 1972, a Voyager mission was created to observe Jupiter and Saturn. It then 
included Uranus and Neptune. The Voyager 1 observed a faint ring around Jupiter's 
equator. The Voyager 2 sent back views on Jupiter's satellites as well as Jupiter, 
the planet.

Significant Dates
1610 -- Italian astronomer Galileo Galilei discovered four moons orbiting Jupiter 
(Io, Europa, Ganymede, and Callisto-the Galilean Satellites).
1973 -- Pioneer 10 passed within 130,354 km of Jupiter (12/3/73); cloud tops and 
moons imaged.
1974 -- Pioneer 11 passed within 43,000 km of Jupiter (12/2/74) providing the first 
images of polar regions.
1979 -- Voyager 1 passed within 350,000 km of Jupiter (3/79) and discovered a faint 
ring and three moons.
1979 -- Voyager 2 passed within 650,000 km of Jupiter (7/79) providing detailed 
imagery of Jovian ring and Io volcanism.
1989 -- Galileo spacecraft launched (10/18/89).
1995 -- Galileo arrives at Jupiter (12/9/95); atmospheric entry probe survives to 
pressure depth of 23 bars.
1999 -- Galileo orbits in Jupiter's system, studying planet, rings, satellites, and 
magnetosphere.

Atmosphere: 
      Jupiter was being observed as early as 1610. The first patterns that were 
observed were east west parallel bands extending out across the planet. The colors 
range from pale yellow and brown to blue and white. These early observers were also 
able to track main features of the planet, such as a specific cloud that would cross
its face in less than five hours. By learning more about the rotation rates of other 
features, we learned that there is a strong eastward motion near the equator of 
Jupiter. The king of the planets is aptly named because it not only has the most 
dynamic atmospheric motion but also the most riveting cloud patterns and storms. 
The dramatic appearance of Jupiter stems partially because the composition of 
Jupiter's atmosphere includes complicated molecules such as ammonia and methane, 
as well as simple molecules such as helium, hydrogen, and sulfur. The composition 
includes exotic molecules such as germain as well. The atmosphere of Jupiter is 
only a narrow surface layer, with three cloud decks found at different levels in 
the troposphere. Hazes of smog can be found higher in the atmosphere.

Clouds:
      Observers reasoned that since Jupiter is five times farther than Earth is 
from the sun and the area which light spreads is the entire sphere surrounding the 
sun, the solar energy per unit area at Jupiter is diluted by more than 25 times. 
This means that the average cloud top temperature must be colder than -150 degrees 
Celsius. If this is so, then what material can form these clouds? Definitely not 
water in such a cold atmosphere, because then water could not melt and the clouds 
could not be constantly changing. Chemists predict that the clouds are actually 
made up of white ammonia ice crystals, formed by the combination of hydrogen and 
nitrogen. 

Interior: 
      Most of Jupiter's interior is liquid hydrogen and helium. The central 
temperature is between 13,000-35,000 degrees Celsius, and the central pressure is 
about 100 million Earth atmospheres. Normally, hydrogen does not conduct heat or 
electricity very well, which are defining characteristics for a metal. And 
therefore, under normal conditions hydrogen is not a metal. Under extreme pressures 
deep within Jupiter, theory suggests that electrons are released from hydrogen 
molecules and are free to move about the interior, causing hydrogen to behave as 
a metal. It then can conduct both heat and electricity. The core of Jupiter is 
believed to be iron silicate that is surrounded by the liquid metallic hydrogen. 
The intense magnetic field of Jupiter is thought to result from the electrical 
currents in this region of metallic hydrogen. It is spinning rapidly and is thought 
to compose 75% of the planet's mass. The outer layer is liquid molecular hydrogen. 
The outer layer of the planet is believed to consist of water droplets, ice 
crystals, Ammonium hydrosulphide crystals, ammonia crystals and cloud tops. 

      High winds blow in opposite directions adjacent to the bands on Jupiter's 
surface. Jupiter has a strong magnetic that allows it to trap atomic particles and 
form the Van Allen belts. These belts contain enough radiation to kill a person. An 
interesting discovery about Jupiter is that it has much less water than we had 
previously expected. Jupiter has less water than even the sun.

Energy:
      There are many theories for the energy source of Jupiter. It loses a large 
amount of heat in relation to its supply, which means that the planet must have 
some source that compensates for its loss. Jupiter radiates 1.6 times as much 
energy as falls on it from the Sun. This means that Jupiter has an internal heat 
source. It is believed that this heat is residual and left over from the original 
collapse of the primordial nebula to form the Solar System, but some may come from 
slow contractions (liquids are highly incompressible, so Jupiter cannot be 
contracting very much.) This internal heat source is presumably responsible for 
driving the complex weather pattern in its atmosphere, unlike the Earth where the 
primary heat source driving the weather is the Sun. Another possible source could 
be the conversion of gravitational potential energy to heat. 

       Jupiter has a large, complex, and intense magnetic field that is thought 
to arise from electrical currents in the interior. The Earth has a strong magnetic 
field, but Jupiter's magnetic field ten times stronger than that of the Earth.

The Magnetic Field:
      The magnetic field is doughnut shaped (or toroidal). It contains larger 
versions of the Earth's Van Allen Belts that trap high-energy charged particles. 
These belts are flattened into plasma sheets in the case of Jupiter. The field 
rotates approximately every 9 hours. The satellites Amalthea, Io, Europa, and 
Ganymede all orbit through this region. 

       The magnetosphere of Jupiter is enormous. Interacting with solar winds of 
charged particles from the sun, it forms a bow shock, like that produced by the bow 
of a ship in water that deflects the charged particles of the solar wind. The 
magnetosphere is strongly affected by the solar wind, pulsing in shape and size. 
It can shrink to about a third of its maximum size when the solar wind is strong. 

       Intense auroras have been observed on Jupiter. Since the bow shock of 
Jupiter's magnetosphere deflects solar wind away from Jupiter's atmosphere, the 
charged particles responsible for the auroras must come from another source. They 
are thought to originate from the innermost satellites that orbit the region with a 
strong magnetic field and trapped charged particles. In fact, they have found that 
the auroras are caused by Io. Io is linked by an electrical current of charged 
particles called an "flux tube" to Jupiter. The charged particles that are ejected 
from Io by volcanic eruptions, flow along Jupiter's magnetic field lines, which 
thread through Io, to the planet's north and south magnetic poles. These charged 
particles hit the atmosphere of Jupiter and interact with the hydrogen gas, 
it glows, or makes auroral emissions. Those bright spots are called footprints. 
They change in brightness and structure as Jupiter rotates.