|Orbital period||42 hours|
|Discovered||January 8, 1610|
Io 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 water of any known astronomical object in the Solar System.
|Moons of Jupiter|
|Ganymede • Callisto • Io • Europa|