This is a composite of the Jovian system and includes the edge of Jupiter with its Great Red Spot and Jupiter’s four largest moons.
A semi-circular view of Europa, with its light blue and brown surface marked with brown lines.

Moons of Jupiter

Jupiter has 95 moons that have been officially recognized by the International Astronomical Union. But the number doesn't capture the complexity of the Jovian system of moons, rings and asteroids. The giant planet has thousands of small objects in its orbit. Scientists are getting so good at spotting tiny moons orbiting distant, giant planets that the International Astronomical Union has decided the smallest will no longer be given mythological names unless they are of “significant” scientific interest.

Explore all of Jupiter's moons


Jovian System

First Discoveries

Jan. 7, 1610

Moon Count


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Europa Clipper

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Featured Moons

Jupiter's four largest moons were the first moons discovered beyond Earth. They are called the Galilean satellites after Italian astronomer Galileo Galilei, who is credited with their discovery in 1610. German astronomer Simon Marius observed them around the same time, but is largely forgotten because he published his findings after Galileo. But the names Marius proposed for the moons in 1614 (mythological characters associated with Jupiter, suggested to him by fellow astronomer Johannes Kepler) are the ones we use today — Ganymede, Callisto, Io, and Europa. Here they are in order of size:

A half-globe view of Jupiter's moon, Ganymede. The moon is gray with a big crater on the right side of the image. The moon also has streaks of lighter and darker materials.


Ganymede is Jupiter's largest moon, and the largest moon in our solar system. It's even bigger than Mercury, and Pluto. 

Bright scars on a darker surface testify to a long history of impacts on Jupiter moon Callisto in this image of Callisto from NASA Galileo spacecraft.


Callisto is Jupiter’s second largest moon and the third largest moon in our solar system.

Partially lit moon Io.


Io is Jupiter's third largest moon, and the most volcanically active world in our solar system.

A half disc view of Europa shows crisscrossed lines on the icy surface.


Europa is Jupiter's fourth largest moon. It's about 90% the size of Earth’s Moon.

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