Final answer:
Europa, one of Jupiter's moons, may have a saltwater ocean beneath its surface due to the planet's gravity generating enough heat to keep the water in liquid form. This makes Europa a significant target for astrobiologists.
Step-by-step explanation:
Jupiter's moon Europa may have a saltwater ocean beneath its surface. The icy crust of Europa conceals an ocean with a depth of tens to perhaps a hundred kilometers. The presence of liquid water on Europa is due to the planet's massive gravity, which generates enough heat to keep the water in liquid form. This discovery has made Europa one of the most interesting moons for astrobiologists.