The Solar System is the Sun and all objects gravitationally bound to it. Its outer boundary is roughly a sphere with a radius of some 100,000 AU, centered on the Sun, that marks the furthest extent of the Oort Cloud. The Sun is overwhelmingly the dominant object. Planets, satellites, and all interplanetary material together comprise only about 1/750 of the total mass. Geochemical dating shows that the Solar System chemically isolated itself from the rest of the Galaxy some 4.7 billion yr ago.