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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


The largest moon in the solar system, this icy world is the only moon to have its own magnetic field – and the atmospheric auroras that come with that.

Jupiter’s icy moon Ganymede is the largest moon in our solar system, even bigger than the planet Mercury, and the dwarf planet Pluto. There’s strong evidence that Ganymede has an underground saltwater ocean that may hold more water than all the water on Earth's surface. It might even have ice and oceans stacked up in several layers like a club sandwich.

Ganymede is the only moon known to have its own magnetic field – something typically found on planets like Earth. The magnetic field causes auroras, or bright ribbons of glowing gas, that circle the moon’s poles.

pioneer 10, 1973
galileo, 1996
Jupiter's moon Ganymede appears as a fuzzy, yellowish ball against a black background in this image taken by the Pioneer 10 spacecraft.
NASA's Pioneer 10 had its closest encounter with Jupiter on Dec. 3, 1973. It was the first spacecraft to obtain close-up images of Jupiter, and three of its largest moons: Ganymede, Callisto, and Europa. Seen here, Ganymede appears fuzzy and yellowish.
NASA
A brownsh gray sphere, shaded on the left side, appears against a black background. It's mottled with dark patches in the upper half, while the lower half is spotted with beight, white mars, some with rays extending from them like paint splatters.
Jupiter's moon Ganymede appears as a fuzzy, yellowish ball against a black background in this image taken by the Pioneer 10 spacecraft.
NASA's Pioneer 10 had its closest encounter with Jupiter on Dec. 3, 1973. It was the first spacecraft to obtain close-up images of Jupiter, and three of its largest moons: Ganymede, Callisto, and Europa. Seen here, Ganymede appears fuzzy and yellowish.
NASA
A brownsh gray sphere, shaded on the left side, appears against a black background. It's mottled with dark patches in the upper half, while the lower half is spotted with beight, white mars, some with rays extending from them like paint splatters.
pioneer 10, 1973
galileo, 1996

two views of Jupiter's moon

Ganymede, As Seen by Pioneer 10 and Galileo

Pioneer 10, NASA's first mission to the outer planets, had its closest encounter with Jupiter on Dec. 3, 1973. It was the first spacecraft to obtain close-up images of Jupiter, and three of its largest moons: Ganymede, Callisto, and Europa. Seen here, Ganymede appears fuzzy and yellowish. Two decades later, the Galileo spacecraft captured this view during its first encounter with Ganymede, on June 26, 1996. The finest details that can be discerned in this picture are about 8 miles (13.4 kilometers) across. The dark areas are the older, more heavily cratered regions and the light areas are younger, tectonically deformed regions. The brownish-gray color is due to mixtures of rocky materials and ice. Bright spots are geologically recent impact craters and their ejecta. Credits: NASA and NASA/JPL

Ganymede – A Fresh Look

Several NASA probes have explored Jupiter and its moons, including Ganymede. The Juno spacecraft was most recent, taking detailed photographs of Ganymede in June 2021.

Images taken by Juno on June 7, 2021, provided a fresh look at features on Ganymede’s surface including craters, clearly distinct dark, and bright terrain, and long structural features possibly linked to tectonic faults. Deep inside Ganymede, there’s a metallic iron core that generates the moon's magnetic field. A shell of rock surrounds the core, and another icy shell surrounds the rock.

There is evidence Ganymede has a tenuous oxygen atmosphere.

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