Jupiter is classified as a Gas Giant planet, meaning that it is mainly composed of gases; hydrogen with a little helium mixed in and trace amounts of other elements. It does have a solid core, made of different materials and thought to be roughly 12 times or more the mass of the Earth. Interestingly, stars are made mainly of hydrogen and helium, so what sets Jupiter apart from being a star? A couple of things: Firstly, its mass; Jupiter would have to be 60 times larger to qualify as a star. Secondly, the source of heat and light coming from Jupiter is internal, and not as a result of nuclear fusion, like our sun. If Jupiter were 60 times more massive, gravitational forces would be strong enough to initiate nuclear fusion.
One of the most noticeable features of Jupiter is the Great Red Spot. This spot is created by a massive storm that has been going for several hundred years. The Great Red Spot is wider than two planet Earths side by side.
Jupiter has 63 known moons, but four are large enough to be of note; Io, Europa, Ganymede and Callisto. The Galileo spacecraft, the only space mission dedicated to Jupiter, orbited the planet for 7 years enabling us to glimpse up close and personal the Shoemaker-Levy comet’s collision with the planet and to gain some spectacular photographs of its larger moons.
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