Jupiter was named after the Roman King of Gods because it is the largest planet in our Solar System in both volume and mass.  Jupiter's diameter is 142,980 kilometers, and its mass is 318 times that of Earth.  It is 778,000,000 kilometers from the Sun, and its period of revolution is 12 years. It has a magnetic field.  It is mainly composed of gasses and has a low density of 1.3 grams per cubic centimeter.  However it does have a rocky core, a layer of ice, a layer of hydrogen in liquid metallic form, and an outer layer of molecular hydrogen.  The uppermost cloud layer is composed of frozen ammonia crystals and the temperature there is about 140 K.  The rotation about its axis is the fastest in the Solar System, taking only 10 hours.

A particular feature of Jupiter is the a Great Red Spot.  The most recent theory states that it is a huge counterclockwise hurricane lasting hundreds of years.  The area of this spot is larger than Earth.

Jupiter has at least 16 known moons.  4 are large and 12 are small. The four closest to the planet are small and have prograde orbits.  The largest moons were discovered by Galileo in 1610 and are called Galilean moons.  Ganymede is the largest moon in the Solar System.  The other large moons are Io, Europa, and Callisto.  Io has many active volcanoes.  Europa is covered with a thick crust of ice.  Ganymede and Callisto have cratered surfaces.  In addition, Jupiter has a faint planetary ring of dust.  Is there life on Europa?  Click below to find out.

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