The "Dagwood Sandwich" Moon. Earlier models of Ganymede's oceans were based on the assumption that the existence of salt didn't change the nature of liquid very much with pressure. However, Dr. Vance and his colleagues found, through laboratory experiments, that salt does increase the density of liquids under the extreme conditions hidden deep within Ganymede and similar icy moons with subsurface bodies of water. Imagine adding table salt to a glass of water. Instead of increasing in volume, the liquid will actually shrink and become denser. The reason for this is that salt ions lure water molecules.
"For the smaller craters, it's like if you're filling a bucket, eventually your bucket gets full, but if you keep pouring cups of water into the bucket, you can't tell how many cups of water beyond full you've gone. Looking at the larger craters at the subsurface might give us insight, because that 'bucket' isn't full yet," Dr. Soderblom added.
A moon is defined as a natural satellite in orbit around another body that, in turn, is in orbit around its Star. The moon is kept in its position by both its own gravity, as well as its host's gravitational grip. Some planets have many moons, some have only a small number, and still others have none at all. Several asteroids inhabiting our Solar System are circled by very small moons, and some dwarf planets--such as Pluto--also host moons.