Io

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Io /ˈaɪ.oʊ/[7] (Jupiter I) is the innermost of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon, has the highest density of all the moons, and has the least amount of relative water of any known object in the Solar System. It was discovered in 1610 and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.