How does gravity affect the solar system?
This figure shows how the mass of the sun creates a distortion in the space time continuum.
This picture shows earth's distortion in the space time continuum. The sun exerts a constant gravitational pull upon the earth. The earth, according to Newton's first law of motion, wants to move straight forward except the sun exerts just enough force upon the earth to alter the straight forward direction, this is also mentioned in Newton's first law as the "outside force."
With the earth moving at a constant speed and the sun's gravity pulling at a constant force the equation is balanced, the orbit is unchangeable unless the earth slows down, not possible, or the sun's gravity changes, also not possible since gravity is a factor of mass.