Ganymede (Jupiter III)
Ganymede is Jupiter's largest moon, and indeed the largest moon in the entire solar system; it is larger in diameter than Mercury but only about half its mass.
Ganymede is one of Jovian moons most hospitable to life. Its internal heat raises its temperature higher than would be expected from solar radiation, while interactions between its ocean, volcanoes and biosphere have produced an oxygen-rich atmosphere, though one that also has a high sulfur content.
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