Io: Moon Over Jupiter . ... Credit Copyright: . Credit: Cassini Imaging Team , Cassini Project , NASA Explanation: How big is the Jovian moon Io ? ... Although in the picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter . That puts it nearly 350,000 kilometers above Jupiter's cloud tops , roughly equivalent to the distance between Earth and Moon . ...