The Solar System formed 4. 6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
In fact, it may be much more reasonable to suppose that the American government's real capabilities in space exceed anything we have heard about, or can easily believe. Cassini's successful mission of exploration to the Saturn system is over, but planetary scientists are left with a cornucopia filled with important new information that Cassini/Huygens sent back to Earth before its mission ended. A collaborative NASA/European Space Agency/Italian Space Agency mission, the robotic spacecraft was made up of two components. The first was the European Space Agency's (ESA's) Huygens Probe, that had been named in honor of the Dutch mathematician and astronomer Christiaan Huygens (1629-1695), who discovered Titan. The Huygens Probe also closely observed Saturn's lovely system of gossamer rings. The second component, the NASA-designed Cassini Orbiter, was named after the Italian-French astronomer Giovanni Dominico Cassini (1625-1712), who discovered four of Saturn's other intriguing, numerous, and icy moons. Using computer models, the team of scientists came up with a complex interior structure for Ganymede, composed of an ocean sandwiched between up to three layers of ice--in addition to the very important rocky seafloor. The lightest ice, of course, would be on top, and the saltiest liquid would be heavy enough to sink to the bottom. Furthermore, the results suggest the existence of a truly weird phenomenon that would cause the oceans to "snow" upwards! This bizarre "snow" might develop because, as the oceans swirl and churn, and frigid plumes wind and whirl around, ice in the uppermost ocean layer, called Ice III, may form in the seawater. When ice forms, salts precipitate out. The heavier salts would then tumble down, and the lighter ice, or "snow," would flutter upward. The "snow" would them melt again before reaching the top of the ocean--and this would possibly leave slush lurking in the middle of the moon's odd sandwich!