All About Jupiter
Galileo was subsequently placed under house arrest for the rest of his life for
Jupiter is the largest of all the planets. It is so big it could swallow all the other planets together. It is almost 143,000km across at the equator.If Jupiter were any bigger it would turn into a star!Jupiter was named by the Romans as lord of the planets. In Greece this is the equivalent to Zeus, and was the original namesake of the weekday that would come to be known in English as Thursday.Jupiter is the 5th planet out from the Sun. It lies between Mars and Saturn, at nearly 780 million km. It takes almost 12 Earth years to make one complete orbit.Jupiter is not a solid rocky planet like the Earth, but instead is a 'gas giant' composed mainly of hydrogen and helium gas.The pressure towards the centre has made the gases turn almost solid, but not rock.What we see of Jupiter is simply the top of the clouds. Different layers combine to make belts crossing the surface.Despite its massive size, Jupiter rotates very quickly; one day on Jupiter lasts for about 10 hours.This rapid spinning has caused the planet to bulge at the equator, so that the radius at the equator is 72,000km while at the poles it is only 67,000km. This flattened shape is clearly visible from Earth.Jupiter is a very turbulent place, high winds blow in every direction stirring up the cloud belts.This stirring causes anomalies in the upper clouds. One such anomaly has created an anticyclone storm that has lasted for over 300 years. We call it 'The Great Red Spot'.The great red spot is over 10 times bigger than the Earth. It was probably first observed by Giovanni Cassini, who described it around 1665.It was Galileo who first turned a telescope toward Jupiter, and on January 7, 1610 he observed 4 bright spots moving around the planet over a succession of nights.He deduced that these were in fact Moons orbiting around the planet. His discovery caused a major outcry with the church when he declared that the Earth was not the centre of the universe, but instead was a planet travelling around the Sun.He was subsequently placed under house arrest for the rest of his life for heresy.We now know that what Galileo saw were the four largest moons of Jupiter : Ganymede, Callisto, Io and Europa. Jupiter has at least 60 moons and counting.The four Galilean moons are huge and are all completely different from each other in structure.Ganymede is the largest of the Moons at over 5262km in diameter. It is composed of silicate rock and water ice, with an ice crust floating over a warmer ice mantle.Callisto is the second largest at 4820km in diameter. Callisto is also the least dense of the Galilean moons. It is one of the most heavily cratered satellites in the solar system, and has one major feature, a basin around 3000 km wide called Valhalla, which probably dates back to the formation of Callisto's crust.Io is the closest of the four moons to Jupiter and the second smallest. But Io is still the fourth largest moon in the solar system and it is also the most volcanically active body in the solar system, with the largest recorded volcanic eruptions.It is believed that if life exists in the solar system other than on Earth then Europa is the most likely candidate. Europa is a strange world. It is completely covered in a layer of ice up to 100km thick, with possibly a liquid ocean beneath. The core of Europa is keeping the ocean from melting and so there may be underwater volcanic geysers similar to those under the Earth's oceans.Over millions of years, Jupiter's size has protected the Earth and the other inner planets from catastrophic impacts from comets and meteors by acting as the solar systems cosmic vacuum cleaner.As it travels around in its orbit it sweeps all interstellar debris before it.Proof of this occurred in 1994 when a comet known as Shoemaker-Levy 9 got a little careless near to Jupiter. (This was the 9th Com
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