An Icy Nest Of Space Eggs. Methone is actually only one member of an icy nest of Space eggs, which also includes the very strange and smooth moons of Saturn, Pallene and Aegaeon. Aegaeon is a very, very small moonlet that also twirls around between Mimas and Enceladus. Like Methone, Aegaeon displays a mysteriously unblemished surface.
This gigantic "King of Planets" is considered by some astronomers to be a "failed star". It is about as large as a gas giant planet can be, and still be a planet. It is composed of approximately 90% hydrogen and 10% helium, with small amounts of water, methane, ammonia, and rocky grains mixed into the brew. If any more material were added on to this immense planet, gravity would hug it tightly--while its entire radius would barely increase. A baby star can grow to be much larger than Jupiter. However, a true star harbors its own sparkling internal source of heat--and Jupiter would have to grow at least 80 times more massive for its furnace to catch fire.
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.