Another Ocean in Space: Jupiter's Moon Ganymede

Hot on the heels of the announcement that hydrothermal vents have been found on Saturn's moon Enceladus, we get another watery alien world announcement: Indirect evidence has been found for a salty ocean under the surface of Jupiter's moon Ganymede! Ganymede is a huge moon, bigger than Mercury, and edging in on Mars-sized territory (Ganymede is 5,270 kilometers in diameter; Mercury is 4,880 and Mars 6,780). Its density is low, meaning it probably is a mixture of rock and ice--that's common for m...