Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Our Solar System is a planetary system that consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud. The principal component of the Solar System is the Sun, a main-sequence G2 star that contains 99.86 percent of the system's known mass and thus dominates it gravitationally. The inner Solar System includes the four terrestrial planets and the asteroid belt, while the outer Solar System is beyond the asteroids, including the four gas giants. Learn more about the Solar System, the most popular models of its formation 4.568 billion years ago as well as its subsequent evolution in the following pages.