Jupiter
main page
Mercury
Venus
Earth
Mars
Asteroides belt
Saturn
Uranus
Neptune
Pluto
Sun
Jupiter, named rightly for the greatest of the Roman gods, is very close to the dividing line between planets and stars. Many, many times larger than the Earth (and containing more mass than all of the other planets, moons, etc except for the sun), Jupiter is so massive that it has been able to hold onto an extremely thick atmosphere, including massive quantities of hydrogen, which is light enough to escape from Earth relatively easily. This gaseous planet is especially composed by Hydrogen and Helium. Jupiter is 778'600'000 km far from the sun. The diametre of this enormous planet is 142'984 km, more than ten Earth. The volumic mass of this planet is 1.32kg/litre. The average of the temperature is -110°C. The atmosphere, like the planet is especially composed by hydrogen, and helium. By calculating the density of matter needed to initiate fusion, it can be seen that Jupiter is nearly large enough, although it would only be a small, weak star, many times dimmer than the Sun.
Nevertheless, it can be shown that Jupiter does have some internal energy of its own, as it gives off more energy than it receives from the sun (the only planet to do so). Unfortunately, the dense atmosphere, severe storms, and awesome gravity of Jupiter make a landing impossible even for unmanned craft, and in fact even makes it impossible to determine if there is actually a solid surface (although one is believed to exist based on other evidence).
Far more interesting about Jupiter are its moons. In total, there are 16, but the four largest, known as the Gallilean Moons after their discoverer 390 years ago, are by far the most intersesting. The smallest, Io, is about the size of our Moon, and is extremely volcanically active, with volcanoes spewing sulfuric ash across the whole of the planet. Ganymede, the largest, is larger than Mercury and Pluto. While having the dry, cratered look of our moon, density and other indicators point to the surface being made largely of water ice, and recent studies by the Gallileo probe have indicated that it might have a vast salty ocean under the surface. Like Ganymede, although smaller, Callisto is largely ice with a rocky core. For biologists, Europa is by far the most promising body in the solar system. With a surface of water ice and extremely strong evidence of a salty ocean beneath, many believe life could spawn near thermal vents or other sources of energy. In the cases of all of the water-bearing moons, the possibilities for human uses are almost unlimited, as they supply water, oxygen, and rocket fuel in almost unlimited quantities.
Jupiter has rings like Saturn's, but much fainter and smaller. They were totally unexpected and were only discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth a quick look to see if any rings might be present. Everyone else thought that the chance of finding anything was nil, but there they were. It was a major coup. They have since been imaged in the infra-red from ground-based telescopes and by Galileo.
