Interior of Europa. Computer artwork of the interior of Europa, a moon of the planet Jupiter. This moon has a small metal core (silver) surrounded by a large layer of rock (beige). Around this, near the surface, is a layer of water (blue). Europa's surface is a smooth layer of ice, which bears very few impact craters. It is thought the water is kept liquid beneath the surface ice by heat from the tidal effects that Jupiter's gravitational field induces in Europa's interior. Major meteorite impacts would melt the ice, and the water would re-freeze as a smooth layer, which explains the lack of surface features on Europa.