Newton steps in

Newton's second law says that the body will accelerate, or change its speed, at a rate that is proportional to the force. Acceleration is twice as great if force is twice as great. 

The acceleration is also smaller the greater the mass of the body. (The same force acting on a body of twice the mass will produce half the acceleration).

Newton also tells us the farther apart the bodies, the smaller the gravitational force.

His law of gravity says that the gravitational attraction of a star is exactly one quarter that of a similar star at half the distance. If the law were that the gravitational attraction of a star went down faster or increased more rapidly with distance, the orbits of the planets would not be elliptical, they would either spiral in to the sun or escape from the sun.