Part of the core of the planet is comprised of a very small, rocky, metallic sphere, although the bulk of the core is liquefied hydrogen and helium gas (not unlike that of a star). The liquefied gas at the core is under such pressure it has a metallic property to it, causing the electrons to move from one hydrogen atom to another. The flow of electrons is not unlike the flow of electrons in electrically conductive material on this world, creating a very strong electrical field which in turn creates the gigantic magnetosphere which is felt at over four million miles from the planet.
The planet rotates so fast (less than ten Earth hours) that it has a large bulge in the middle. This bulge is caused by the centrifugal force exerted by its mass in the quick rotation. The planet's poles actually rotate slower than does the equatorial region, because unlike the terrestrial planets, there is no solid matter (crust) to hold everything in sync, the gases of the poles are always trying to catch up with the rotation of the center of the planet.
Jupiter has the most satellites of all the planets, sixty three at last count, the most interesting are the four Galilean moons. Io currently has the most active volcanoes in the solar system, mostly caused by the tidal effect of Jupiter's tremendous gravity. The other three Galilean moons are covered with a thick layer of ice of varying composition. It is believed that the moon Europa may have a liquid salt water sea beneath its ice sheet. This is evidenced by what appears to be rafting of the surface ice sheets, similar to that of the Earth's salt water ice sheets, this rafting is evidenced when an iceberg moves. Because of the possibility of a liquid salt water ocean beneath the surface and the further possibility of volcanic vents being the cause of the liquefied ocean, scientist believe Europa gives us the best chance of finding complex life forms in our solar system.
It is hard to think of Jupiter or the other gas giants as planets because they lack the solid terra firma surface of the inner terrestrial planets. If Jupiter were much larger than it is, it would most certainly of had enough pressure at its core to possibly ignite the hydrogen into a nuclear furnace, but would most likely just be a brown dwarf (16) (there are many more brown dwarf stars then astronomers realize in the Universe). If that were the case, we would be living in a binary star system and the Earth would be a much hotter world than it is today, but probably still habitable.
The atmosphere of Jupiter is primarily comprised of hydrogen gas, about eighty percent with most of the other twenty percent consisting of helium gas. There is also trace amounts of methane, ammonia and oxygen which combine with the hydrogen to form trace amounts of water and hydro-sulfide gas.
Probably the most notable feature of Jupiter is the Great Red Spot, which has been observed from Earth for over three hundred years. This spot is actually a storm, a large tornado three times the size of Earth.
The Upper atmosphere of the planet is observable as bands or layers. These bands are the result of winds (in excess of four hundred miles per hour) moving in opposite directions around the planet. The bands are actually comprised of the different gases being layered in the atmosphere, creating the different hues to the rings.
The sixth planet in our solar system, Saturn, was believed to be the outermost and last planet in the solar system until the discovery of Uranus by British astronomer William Herschel. Originally the sixth planet was named Kronos by the ancient Greeks, the planet was renamed later by the Romans to the name we know it by today. Saturn has the second largest planetary diameter, but at the same time it has the lowest density of all the planets. The density is so low in fact, the planet would actually float in water. The composition of Saturn is very similar to that of Jupiter, consisting of gases and liquids, the atmosphere is also similar to that of Jupiter, consisting primarily of hydrogen gas.
A year on Saturn takes about twenty nine and a half Earth years (trip around the Sun), conversely a day on Saturn (tilt of twenty seven degrees) is a quick ten Earth hours. This rapid rotation causes the gaseous planet to bulge heavily at the equatorial region (like Jupiter), more than ten thousand miles larger at the equator than the circumference of the poles. The core of Saturn is believed to be a small rocky ball with very little mass.
Saturn is probably best known for its brilliant rings, the rings are thought to be the remnants of a moon (or many moons) that was caught inside the Roche limit. The bright, brilliant color comes mostly from ice crystals included in the rings, reflecting much of the light (photons) and radiation from the Sun. The mass of the rings is very small, mostly just fine dust particles. Saturn has the second most satellites, last count is forty eight.
Uranus was discovered by William Herschel in 1781. When he first observed the planet he mistakable thought it to be a comet. After it was finally determined to be a planet, Herschel was given the honor of naming the newly found celestial body. He named the planet Georgium Sidus (George's Star) in honor of King George III. The name was not accepted well by the populous though, believing it to be presumptuous to name a celestial body after a mere man. For years, the populous simply referred to the planet as Herschel. Upon Herschel's death in 1822, the planet was formally renamed Uranus, following in the tradition of naming celestial bodies after Greek mythology.
At last count there are twenty seven known moons circling the planet. A year on Uranus last a little over eighty four Earth years. The planet is sitting cock-eyed on a ninety eight degree tilt, this orientation means the poles face the Sun, rather than the equator. The rotation of the planet takes about seventeen hours, again this fast rotation causes the center to elongate, only this time because of its orientation it is the poles that are elongated.
Neptune was not discovered as a planet until 1846. A year on Neptune last nearly one hundred sixty five Earth years, that means only one Neptunium year will have passed by 2011 since it was first discovered.
There are thirteen known moons with more to be found, because the Kuiper Belt crosses paths with both Uranus and Neptune there is a strong possibility that many of the moons are actually 'caught' asteroids from the belt. The dwarf planets found in the Kuiper Belt actually carries their orbit's through the orbit's of both Uranus and Neptune.
The atmosphere of the two outer planet's contain a measurable amount of methane, making them slightly different in composition than Jupiter and Saturn. Some astronomers have suggested these two planets should not be referred to as Jovian planets because of the different composition of their atmosphere.
Neptune's most interesting moon may be Triton, as it is believed to have the possibility of some life forms. The remoteness (distance) of the outer gas giants and the harsh conditions found on these planets, make them only accessible to orbital or plunging probes, as nothing can survive entering far into the atmosphere of these two planets.
THE OUTER LIMIT'S
The Kuiper Belt lies beyond Neptune and is what most believe to be the outer edge of our solar system (the area influenced by the Sun's gravity). The Kuiper Belt consist of asteroids and many dwarf planets, including Pluto. After astronomers were able to accurately calculate the mass of Pluto to be less than that of our Moon, along with the discovery of even larger planetary masses in the Kuiper Belt, Pluto was demoted to the status of dwarf planet in 2006.
Pluto normally resides in the Kuiper Belt along with several other bodies of equal or larger mass, discovered in 1930 (at an Arizona observatory), Pluto was called the ninth planet, but as noted poor Pluto has since been demoted to the category of dwarf planet.
The Kuiper Belt consist of large meteors, asteroids, comets and the infamous Pluto, along with several other dwarf planets. The Kuiper Belt is more of the remnants of the matter that made our solar system, the left-overs that are trapped by the gravitational influence of the entirety of our solar system from the center, which is our Sun of course (early teachings believed the Earth to be the center of all that existed in the sky). As mentioned, the Kuiper Belt is on the outer edge of our solar system, but not actually the far reaches of our solar sys
tem, there are comets, dwarf planets and asteroids whose orbit's are at times outside the Kuiper Belt in an area called the Oort Cloud, at other times these orbits are inside the outer most planets of Neptune and Uranus.
As stated, larger bodies than Pluto have been found in the Kuiper Belt, one of these being the dwarf planet Eris, like Pluto Eris has a very eccentric orbit, at times bringing its orbit inside the orbit's of Neptune and Uranus on its closest swing to the Sun, at other times its orbit is way beyond the Kuiper Belt at its farthest, way out in the Oort Cloud (the area believed by most to be the true outer limit of our solar system). Little is known of these dwarf planets that reside in the Kuiper Belt, as they are so far from Earth they have not been even partially explored.
As stated, the Kuiper Belt not only consist of the dwarf planets, but of asteroids and debris left over from the formation of our solar system, much of the same type of debris as the asteroid belt between Mars and Jupiter, but unlike the asteroid belt, also residing in the Kuiper Belt and the Oort Cloud are icy formations or comets. Some of the better known comets to the inhabitants of this world are Haley's, Temple Tuttle and Swift