... Galileo Images of Io . ... Galileo Finds Giant Iron Core in Jupiter's Moon Io . ... The temperature on Io's surface is about -143њ C (-230њ F); however, a large hot spot associated with a volcanic feature measured about 17њ C (60њ F). ... Io's rotation . ... This pair of Hubble images of Jupiter's volcanic moon Io shows the surprising emergence of a 320-kilometer (200-mile) diameter, large yellowish-white feature near the center of the moon's disk (photo on the right). ... Volcanic Plumes . ...