Structure of Europa. Cut-away computer illustration showing the interior of Europa, one of Jupiter's moons. Europa has a small metal core (gold, centre) surrounded by a large layer of rock (orange). The surface is thought to consist of an ocean of liquid water (blue) covered by a thick layer of ice (white). It is thought the water beneath the surface ice is kept liquid by heat from tidal effects induced in Europa's interior by Jupiter's gravitational field. Major meteorite impacts would melt the ice, and the water would re-freeze as a smooth layer, which explains the lack of surface features.