Jupiter is the biggest planet in our solar system. It is the fifth planet from the Sun.  In 1610, Galileo Galilei, an Italian scientist, was the first person to look at Jupiter with a telescope.  He saw Jupiter’s four largest moons, Callisto, Ganymede, Europa, and Io.  These are called the Galilean Moons.  The Galilean Moons were the first new objects in space found with a telescope.  Jupiter is named after the king of the Roman gods.

Jupiter ranges from 460 million miles (749.3 km) to 507 million miles(815.4 km) from the Sun. Jupiter’s year is 11.9 Earth years long.  The planet day is 9 hours, 50 minutes long in Earth time.  Jupiter’s main atmospheric gases are hydrogen (90%) and helium(10%). Jupiter has 16 known moons.  The planet also has a ring that is hard to see.

Jupiter is a "gas giant".  It has an iron core, then a layer of liquid metallic hydrogen, then a layer of liquid hydrogen.  On top of this is the atmosphere made of water droplets, ice droplets, ice crystals, clouds of frozen ammonia, and hydrogen gas.  This atmosphere swirls and has strong winds and storms.  The Great Red Spot is a giant storm that has gone on for centuries.

Many spacecraft have visited Jupiter. Pioneer 10 and 11, Voyager 1 and 2, and Ulysses helped scientists learn a lot about Jupiter’s atmosphere, magnetosphere, and gravity.  The Galileo spacecraft has been studying Jupiter since 1995.  It sent a  probe to look at Jupiter’s atmosphere.  The Galileo probe has also learned more about the Galilean moons.  It found volcanos erupting on Io and a magnetic field on Ganymede.  Oceans may exist on Callisto and Europa.  NASA has approved  the Millennium Mission which will extend the Galileo Probe's mission to Jupiter and its moons until the end of 2000.

Jupiter Facts

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