NASA/Galileo's moons. The Galilean moons Io. Europa. Ganymede and Callista. "On the 10th, in 1610, the moons appeared in yet another configuration, and on the 11th, Galileo, "arrived at the conclusion, entirely beyond doubt, that in the heavens there are stars wandering around Jupiter like Venus and Mercury around the sun.' With those words, Galileo reported the findings in his explosive little best seller, 'Sidereus Nuncius' (the starry messenger). Scientists now think that all of Jupiter's moons and rings formed from a disk of debris around the newborn planet, just as the planets of the solar system took shape in the disk of leftovers surrounding the infant sun. Similar disks are observed today around other sunlike stars and are presumed to be new planetary systems in the making.