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.
Makemake is about a fifth as bright as Pluto. However, despite its comparative brightness, it was not discovered until well after a number of much fainter KBOs had been detected. Most of the scientific hunts for minor planets are conducted relatively close to the region of the sky that the Sun, Earth's Moon, and planets appear to lie in (the ecliptic). This is because there is a much greater likelihood of discovering objects there. Makemake is thought to have evaded detection during earlier searches because of its relatively high orbital inclination, as well as the fact that it was at its greatest distance from the ecliptic at the time of its discovery--in the northern constellation of Coma Berenices. Cassini is an unmanned spacecraft sent to the Saturn system. It is the fourth space probe to visit the ringed planet, as well as the first to enter orbit. It has been studying Saturn and its many moons since arriving there in 2004. 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!