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 years ago.