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True color image of Jupiter with about half the planet illuminated by sunlight.
A Cassini spacecraft portrait of Jupiter in 2000.

With its numerous moons and several rings, the Jupiter system is a "mini-solar system." Jupiter is the most massive planet in our solar system, and in composition it resembles a small star. In fact, if Jupiter had been between fifty and one hundred times more massive, it would have become a star rather than a planet.

On January 7, 1610, while skygazing from his garden in Padua, Italy, astronomer Galileo Galilei was surprised to see four small "stars" near Jupiter. He had discovered Jupiter's four largest moons, now called Io, Europa, Ganymede, and Callisto. Collectively, these four moons are known today as the Galilean satellites.

Galileo would be astonished at what we have learned about Jupiter and its moons in the past 30 years. Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and has its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. An icy ocean may also lie beneath the crust of Callisto. In 2003 alone, astronomers discovered 23 new moons orbiting the giant planet. Jupiter now officially has 63 moons - by far the most in the solar system. Many of the outer moons are probably asteroids captured by the giant planet's gravity.

Read More About Jupiter

Just the Facts
Distance from the Sun: 
778,412,020 km
Equatorial Radius: 
71,492 km
1,425,500,000,000,000 km3
000,000 kg
Planetary Expressions
Kid's Drawing Jeremy (age 11) drew this picture of Jupiter. Looks pretty good, huh?

Check out the kid-friendly Jupiter page for more images and pictures! Read More...
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