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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. Comets are really traveling relic icy planetesimals, the remnants of what was once a vast population of ancient objects that contributed to the construction of the quartet of giant, gaseous planets of the outer Solar System: Jupiter, Saturn, Uranus, and Neptune. Alternatively, the asteroids--that primarily inhabit the region between Mars and Jupiter termed the Main Asteroid Belt--are the leftover rocky and metallic planetesimals that bumped into one another and then merged together to form the four rocky and metallic inner planets: Mercury, Venus, Earth, and Mars. Planetesimals of both the rocky and icy kind blasted into one another in the cosmic "shooting gallery" that was our young Solar System. These colliding objects also merged together to create ever larger and larger bodies--from pebble size, to boulder size, to mountain size--and, finally, to planet size. Dr. Thomas and his team also note that electrostatic forces could additionally keep the Space egg delightfully soft. Electrons that haunt Saturn's radiation belt could be charging ice crystals on the surface, causing them to rise, while also rendering them more mobile. However, the team of astronomers say that this is still speculation.