All of the water on Jupiter’s moon Europa compared to all of the water on Earth. Scientists’ consensus is that a layer of liquid water exists beneath Europa’s surface. It is estimated that the outer crust of solid ice is approximately 10–30 kilometers (6–19 mi) thick, including a ductile “warm ice” layer, which could mean that the liquid ocean underneath may be about 100 kilometers (60 mi) deep. This leads to a volume of Europa’s oceans of 3 × 1018 m3, between two or three times the volume of Earth’s oceans.
Europa (Jupiter II, diameter: 3,122 km / 1,940 mi) is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet. It has a smooth and bright surface, with a layer of water surrounding the mantle of the planet, thought to be 100 kilometers thick. The smooth surface includes a layer of ice, while the bottom of the ice is theorized to be liquid water. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life. Heat energy from tidal flexing ensures that the ocean remains liquid and drives geological activity. Life may exist in Europa’s under-ice ocean, perhaps subsisting in an environment similar to Earth’s deep-ocean hydrothermal vents or Antarctica’s Lake Vostok. Life in such an ocean could possibly be similar to microbial life on Earth in the deep ocean.