"We are just beginning to try and figure out quantitatively how all this might smooth a surface," Dr. Thomas said in the May 17, 2013 New Scientist.
Ganymede, and four other moons dwelling in our Sun's family, possess liquid water beneath their frigid crusts of ice. The others are Saturn's moons, Titan and Enceladus, and two other Galilean moons of Jupiter--Europa and Callisto. Planetary scientists think the oceans of Europa and Enceladus are in contact with rock--thus making these two moons high-priority targets for future astrobiology missions.
When Jupiter was born along with the rest of our Solar System, approximately 4.56 billion years ago, it twinkled like a star. The energy that it emitted--as a result of tumbling surrounding material--made Jupiter's interior searing-hot. In fact, the larger Jupiter grew, the hotter it became. At long last, when the material that it had drawn in from the whirling, swirling surrounding protoplanetary accretion disk--made up of nurturing dust and gas--was depleted, Jupiter may well have attained the enormous diameter of over 10 times what it has today. It also may have reached a truly toasty central temperature of about 50,000 Kelvin. During that long ago era, Jupiter twinkled, glittered, and sparkled like a little star, shining ferociously with a fire that was approximately 1% that of our much more brilliant Sun today.