Final answer:
Europa is thought to contain a vast ocean of liquid water beneath its icy crust, making it a prime candidate in the search for extra-terrestrial life in Jupiter's moons.
Step-by-step explanation:
The moon of Jupiter thought to contain liquid water somewhere in its interior is Europa. Europa is unique due to the planet Jupiter's massive gravity, which creates tides similar to those on Earth, and the resulting friction generates enough heat to maintain a liquid water ocean beneath a thick ice crust. This subsurface ocean is of great interest to scientists because it presents a possible environment for extra-terrestrial life. Aside from Europa, Ganymede and Calisto, with their high water ice composition, may also have liquid water under their surfaces, but Europa's conditions are considered the most favorable for the existence of life.