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Jupiter: Planets
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Jupiter is the biggest planet in the Solar System and is the first of the four Gas Giants. Earth could fit into Jupiter over 1300 times! The planet has a very strong pull of gravity and a very thin ring spinning around it, just like Saturn's rings only much, much thinner. Jupiter is made up almost entirely of gas. This means that the whole planet is just like sky without any land below it. In this sky are electrical storms (lightning) and winds and hurricanes. Jupiter may have a very small liquid or solid centre which would be only the same size as Earth.
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[F]ar the only spacecraft to orbit Jupiter is the Galileo orbiter, which went into orbit around Jupiter on December 7, 1995. It orbited the planet for over seven years, conducting multiple flybys of all of the Galilean moons and Amalthea. The spacecraft ... witnessed the impact of Comet Shoemaker-Levy 9 as it approached Jupiter in 1994, giving a unique vantage point for the event. However, while the information gained about the Jovian system from Galileo was extensive, its originally-designed capacity was limited by the failed deployment of its high-gain radio transmitting antenna.[74]
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Since Jupiter has no solid surface, no human will ever walk on the planet. In fact, any attempt to visit the Jovian system will require heavy shielding. Jupiter's magnetic field captures electrically charged particles from the Sun and from the planet's volcanic moon Io. These particles create strong radiation belts. Around Io's orbit, the radiation belts are powerful enough to kill an unprotected human in a few minutes. That adds one more item to the list of Jupiter's superlatives: deadliest radiation belts.
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At latest count in May 2005, Jupiter has been found to have at least 63 satellites orbiting outside of its rings. (See an animation of the orbits of many of these satellites around Jupiter, with a table of basic orbital and physical characteristics, or a NASA fact sheet.) In addition to the four innermost moons, the next four are ... the largest, called "Galilean" moons because they were first seen in 1610 by the astronomer Galileo Galilei, who was subsequently persecuted by the Church for suggesting that at least some celestial bodies do not revolve around the Earth. By order of their increasing distance from the giant planet, the four moons are Io, Europa, Ganymede, and Callisto. As with Earth and its Moon, Jupiter's rotation is gradually slowing down from the tidal drag of the large Galilean moons, and these tidal forces are also gradually causing the moons' orbits to move farther away from the planet.
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The magnetosphere of Jupiter is responsible for intense episodes of radio emission from the planet's polar regions. Volcanic activity on the Jovian moon Io (see below) injects gas into Jupiter's magnetosphere, producing a torus of particles about the planet. As Io moves through this torus, the interaction generates Alfven waves that carry ionized matter into the polar regions of Jupiter. As a result, radio waves are generated through a cyclotron maser mechanism, and the energy is transmitted out along a cone-shaped surface. When the Earth intersects this cone, the radio emissions from Jupiter can exceed the solar radio output.[47]
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Jupiter's magnetosphere is huge. It's about 10 times wider than the sun, and its tail, stretched out by the solar wind, extends far beyond Saturn. One day, astronomers expect, this vast magnetosphere is going to flip. The Sun's magnetic field reverses polarity every 11 years; Earth's magnetic field flips, too, every 300,000 years on average. This seems to be normal behavior for magnetic dynamos in stars and planets. When will Jupiter's field flip?
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