... Our Solar System is a stellar-planetary unit consisting of the Sun ; the nine planets and their satellites; the asteroids, comets, and meteoroids; and interplanetary dust and gas. The dimensions of this system are specified in terms of the mean distance from the Earth to the Sun, called the astronomical unit (AU). ... The boundary between the solar system and interstellar space - called the heliopause - is estimated to occur somewhere beyond 120 AU. ... Earth . ...