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.
The team of scientists used data gathered by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, composed of a duo of twin spacecraft that circled Earth's Moon throughout 2012, each measuring the push and pull of the other as an indicator of lunar gravity.
Tracing our Moon's changing porosity may ultimately help astronomers to track the trajectory of the invading army of a multitude of lunar impactors, that occurred during the Late Heavy Bombardment, 4 billion years ago.
Moons, Myths, Etc. Our bewitching, and sometimes bewildering Moon, has long been the inspiration for magical myths, weird legends, bedtime stories, and beautiful poetry. Earth's Moon is a very ancient symbol of femininity, as well as for wild bouts of strange madness and romantic love. Some ancient, traditional legends and childhood stories tell of a man's face etched out on its shining surface, while others tell strange tales of a "Moon Rabbit." Lovely, ancient myths, tales, and bedtime stories aside, Earth's Moon is a very real object. It has been a companion-world to our Earth almost from that very ancient era, when our Solar System was first forming, about 4.5 billion years ago.