The term 'A Moon of Jupiter' refers to two of the four Galilean moons of Jupiter, Europa and Elara. Europa is the sixth-closest moon to Jupiter and is the smallest of the four Galilean moons. It is composed of silicate rock and has a water-ice crust. Elara is the seventh-closest moon to Jupiter and is the third-largest of the four Galilean moons. It is composed of silicate rock and ice and is believed to have an icy mantle.