Jupiter over Europa. The planet Jupiter seen above the horizon of the icy landscape of Europa. Jupiter is shown with a shadow on it cast by it innermost moon, Io (right). The surface of Europa is lit by sunlight reflected from Jupiter. Europa is the smallest of the four Galilean moons of Jupiter, and the second closet to the planet. Its surface is icy and relatively smooth. Impacting meteorites cause melting of the surface, allowing the water to smooth out before re-freezing. There is some evidence of large-scale movements of the ice, possibly supported by a liquid mantle and driven by thermal processes within the moon.