Illustration showing the type, depth, and volume of ocean thought to be on each planet. From left to right: Earth with a surface ocean, Europa and Callisto with possible subsurface ocean, Ganymede with possible layered ice-water ocean, Titan with an ammonia-water ocean and hydrocarbon lakes, Enceladus with possible regional subsurface ocean and geyser beneath south pole, and Triton with subsurface ammonia-water ocean.