I think it's the balance of matter and antimatter interacting creating dark matter which I believe is the basis of gravity.
Wherever there is matter there is gravity. Our Solar System contains a lot of matter, 99% of it is caused the sun. The gravitational forces of the planets are proportional to their mass and they all interact with each other according to Newtons laws of gravitation.
As far as the Solar System is concerned most of its gravity comes from the sun. You must be familiar with the universal law of gravitation F = G(m1)(m2)/r^2 where G is the gravitationa constant, m1 and m2 are masses and r is the (center to center) distance between two objects. Since the sun is the most massive object in the Solar System, it is accounted for the force that places the planets on its orbits.
Tom Cruise and the other Scientologists brought it back from outer space in a big trailer.