The Solar System consists of one star, the nine principal planets, their satellites and lesser bodies such as asteroids, comets and meteoroids, plus a vast amount of thinly-spread interplanetary matter. The centre of gravity of the Solar System lies just outside the surface of the Sun, due mainly to the mass of Jupiter. According to the Nebular Hypothesis, most of the angular momentum of the Solar System would reside in the Sun, which would be in quick rotation; actually, most of the angular momentum is due to the giant planets. Modern theories are much more akin to Laplace’s than to later proposals. It is thought that the Solar System began in a huge gas-and-dust cloud, part of which started to collapse and to rotate–possibly triggered off by the effects of a distant supernova. The Solar System is essentially stable, and will remain so until the Sun leaves the Main Sequence and becomes a giant star.