JUPITER

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Jupiter – the fifth planet in the Solar System is the largest of all. It is interesting to note that since prehistoric times it was adored as the main god… 
Ancient Greeks identified it with Zeus, the god of all atmospheric phenomena, the overseer of family and the state, the maintainer of laws involved in vows and treaties and of course most important of all the father of all gods and people… Zeus was the son of Cronus and Rhea. His brothers were: Poseidon, Hades, Hestia, Demeter and Hera (who were also his wives). They helped him to defeat his father, the Titans, Giants and therefore he shared with them the power over the world… As I have mentioned before the main centers of Zeus’ cult were Dodona and Olympia (the god himself has his at Mount Olympus). His main attribute was the thunderbolt which he used to punish the ones who deserved to be punished. A symbol of Zeus is also the eagle the holy bird and a tree (oak). Ancient Romans worshipped him as Jup(p)iter, who according to olditalic beliefs was the god of bright sky and later had similar functions as in the Greek myths. It is interesting to know that the word ''Jowisz'' – the Polish name for Jupiter – comes from the Latin genetive according to the rule: Jup(p)iter – Iovis.

    As I have mentioned before, Jupiter is the largest planet in the Solar System with a mass exceeding the masses of all other planets and their moons combined (317 greater than the Earth's!). If Jupiter was only several times more massive its mass would be sufficient for the ignition of thermonuclear synthesis in its core and would cause it to become… a star! Even its chemical composition resembles stars…
    Another unusual feature of this planet is the apparent lack of solid surface! In a telescope we can only see a complicated structure (pattern of belts) of outer cloud layers… What’s more the rotational period depends on the latitude. Jupiter rotates the fastest at its equator with a period of less than 10 Earth hours! At higher latitudes the rotational period is a bit longer. Fast spinning causes the planet to flatten with the oblatness noticeable even in amateur telescopes. Jupiter’s equatorial diameter is 142,984 km whereas at the poles it measures only 133,708 km (with a mean diamater of 139,822 km). And this means that Jupiter is over 19 times more oblate than the Earth!
     It has been determined that Jupiter radiates 1.67 times more energy than it gets from the Sun although it is five times furher from it than the Earth. This unusual excess of heat is probably caused by slow cooling of its outer layers originally warmed up by the energy from shrinking in proto-Jupiter when it was forming 4.5 billion years ago. The inner heating and its fast spin make Jupiter’s interior rapidly convective. The hotter places called zones are slowly moving upwards and the darker ones (so called belts) are moving down. One of the unusual features still perplexing scientists is the Great Red Spot in the southern hemisphere. It is a huge (bigger than the Earth!) which has been observed for 300 hundred years before its discovery although it must have existed much earlier... Over all those years its shape and hue were changing but it’s never disappeared completely! It can be obesrved even in moderate amateur telescopes of 10 to 15 centimeters (4'' – 6'')! It is good to spend some time checking its visibility in an astronomical almanach for the time of its transit since it is changing as well: in 2004 its longitude was 84 deg and at its latitude Jupiter’s spin is much slower (the coordinates are rotating in accordance with a so called system II).

    And what is in the planet’s interior, below the clouds? We cannot be absolutely sure but using some high pressure physics and obseving changes in its surface features we are able to speculate on its internal structure…
    If we could only dive into Jupiter’s interior in a very durable bathyscaphe we could probably ascertain ourselves that it has no clear stratification with its „surface” being defined as an outer gas layer at a pressure of 10⁵ Pa (about 1 Bar) and a temperature of –67 degrees centigrade (170 K). The outer layers consist of mainly ammonia NH₃, methane CH₄, NH₄CH, nd also Phosphorus (giving the Great Red Spot its red hue), sulfur and some unstable organic compounds. Slightly lower one could probably find some water vapor clouds.
    Pressure and temperature keep rising… About 1,000 km below the „surface” (which is only 1.4% of Jupiter’s radius!) hydrogen molecules and helium atoms are compressed so greatly that they are beginning to act like a liquid! This does not mean that there are oceans of helium and hydrogen at Jupiter since the transition between gas and liquid is not irreversible and they are also subject to constant mixing of lower and upper layers due to convection… About 14,380 kilometers below (0.78 R) the temperature rises to about 10,000 degrees centigrade and the pressure is 2 million times greater than at the surface of the Earth!
    Under such circumstances hydrogen begins acting like something similar to a solid body and also becomes a good conductor. It therefore becomes metalic! Now we have to travel a long distance of 40,000 km and at 0.2 R we find a core of rock and ice which once was the cornerstone for the formation of proto-Jupiter. It is surrounded by a liquid mix of water, methane and ammonia at a temperature of about 20,000 degrees centigrade. What prevents those liquids from evaporating is the tremendous pressure 45 million times greater than on Earth.

     Above Jupiter, at about 1.4 to 3.15 R, lurk some faint and narrow rings. The had never been seen until the →Voyagers, era since their light is 300,000 times fainter than that of our planet! Another invisible object around Jupiter is its vast magnetosphere ! If we could only glimpse it from Earth it would look like a halo around Jupiter comparable in size to Full Moon! Under the influence of the →solar wind, the magnetosphere widens at its side opposite to the Sun until it reaches the orbit of Saturn! (it is therefore the largest object in the Solar System) Furthermore, we have been also able to see some  →auroras in Jupiter’s magnetosphere…

    There are already over 60 known moons of Jupiter making it the current record-holder in this matter. Four largest ones – Io, Europa, Ganymede and Callisto, owere discovered by Galileo almost 400 years ago! They can be viewed swirling aroung the planet even in binoculars which is a great bit of fun for all amateur astronomers! Larger telescopes will show us other phenomena like a transit of the moon's shadow on the disk of the planet (a really spectacular event!) and mutual occultations every six years (the last series occured in early 2003). Observing other moons is out of reach of amateur telescopes and especially when it comes to the remote moonlets being discovered recently in great quantities...

    The Jupiter system has been explored by Pioneer 10 and 11, Voyager 1 and 2 and also Ulyssess… Those space probes were flying by only for a brief moment and could not carry on any long-term investigation. Only large ground-based telescopes and Hubble Space Telescope are able to view Jupiter for extended periods of time and follow the changes in its appearance. A plethora of information has also been gathered by the Galileo probe which recently finished its mission lasting over eight years! (December 7, 1995 to September 21, 2003)

THE ORBIT OF JUPITER