The Solar System[a] comprises the Sun and the objects that orbit it, either directly or indirectly.[b] Of those objects that orbit the Sun directly, the largest eight are the planets[c] that form the planetary system around it, while the remainder are significantly smaller objects, such as dwarf planets and small Solar System bodies such as comets and asteroids.[d] Of those that orbit the Sun indirectly, two are larger than the smallest planet.
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 most 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.