Newsgroup: it.discussioni.misteri
Titolo: Jupiter

Jupiter
http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html
Jupiter is the fifth planet from the Sun and by far the largest. 
Jupiter is more than twice as massive as all the other planets 
combined (318 times Earth). 
        orbit:    778,330,000 km (5.20 AU) from Sun
        diameter: 142,984 km (equatorial)
        mass:     1.900e27 kg
The gas planets do not have solid surfaces, their gaseous 
material simply gets denser with depth (the radii and diameters 
quoted for the planets are for levels corresponding to a 
pressure of 1 atmosphere). What we see when looking at these 
planets is the tops of clouds high in their atmospheres 
(slightly above the 1 atmosphere level). 
Jupiter is about 90% hydrogen and 10% helium (by numbers of atoms, 
75/25% by mass) with traces of methane, water, ammonia and "rock". 
This is very close to the composition of the primordial Solar 
Nebula from which the entire solar system was formed. Saturn has a 
similar composition, but Uranus and Neptune have much less 
hydrogen and helium. 
Jupiter probably has a core of rocky material amounting to 
something like 10 to 15 Earth-masses. 
Above the core lies the main bulk of the planet in the form of 
liquid metallic hydrogen. This exotic form of the most common 
of elements is possible only at pressures exceeding 4 million 
bars, as is the case in the interior of Jupiter (and Saturn).
Liquid metallic hydrogen consists of ionized protons and 
electrons (like the interior of the Sun but at a far lower 
temperature).
At the temperature and pressure of Jupiter's interior hydrogen 
is a liquid, not a gas. It is an electrical conductor and the 
source of Jupiter's magnetic field. This layer probably also 
contains some helium and traces of various "ices". 
The outermost layer is composed primarily of ordinary molecular 
hydrogen and helium which is liquid in the interior and gaseous 
further out. The atmosphere we see is just the very top of this 
deep layer. Water, carbon dioxide, methane and other simple 
molecules are also present in tiny amounts.
Jupiter would have to be at least 80 times 
more massive to become a star.
 Jupiter has a huge magnetic field, much stronger than Earth's. 
Its magnetosphere extends more than 650 million km (past the
orbit of Saturn!). (Note that Jupiter's magnetosphere is far 
from spherical -- it extends "only" a few million kilometers in 
the direction toward the Sun.) Jupiter's moons therefore lie 
within its magnetosphere, a fact which may partially explain 
some of the activity on Io. Unfortunately for future space 
travelers and of real concern to the designers of the Voyager 
and Galileo spacecraft, the environment near Jupiter contains 
high levels of energetic particles trapped by Jupiter's magnetic 
field. This "radiation" is similar to, but much more intense 
than, that found within Earth's Van Allen belts. It would be 
immediately fatal to an unprotected human being. 
The Galileo atmospheric probe discovered a new intense radiation 
belt between Jupiter's ring and the uppermost atmospheric layers. 
This new belt is approximately 10 times as strong as Earth's 
Van Allen radiation belts. Surprisingly, this new belt was also 
found to contain high energy helium ions of unknown origin. 
Jupiter has rings like Saturn's, but much fainter and smaller. 
Unlike Saturn's, Jupiter's rings are dark (albedo about .05). 
They're probably composed of very small grains of rocky material. 
Unlike Saturn's rings, they seem to contain no ice.
In July 1994, Comet Shoemaker-Levy 9 collided with Jupiter with 
spectacular results. The effects were clearly visible even with 
amateur telescopes. The debris from the collision was visible for
nearly a year afterward with Hubble Space Telescope (HST). 
Jupiter has 61 known satellites (as of May 2003): 
the four large Galilean moons, 34 smaller named ones, 
plus many more small ones discovered recently but not yet
named. 
http://www.ifa.hawaii.edu/~sheppard/satellites/
http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html
Pictures of Jupiter and its Satellites
http://seds.lpl.arizona.edu/nineplanets/nineplanets/pxjup.html
Hubble Space Telescope image of Jupiter 
http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/29/image/b
shows a hurricane twice the size of the Earth.
JUPITER, and the Eye of Horus:
http://home.hiwaay.net/~jalison/bowles.html
Recent Cassini images of Jupiter
http://photojournal.jpl.nasa.gov/target/Jupiter

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