Galileo also, I think, estimated the average distances between stars from the assumption that the stars and the Sun were about equally luminous. The eternal silence of these infinite spaces alarms me. Newton provided the key to the mechanism behind the solar system. Unless a force acts, an object continues at rest or moves at a constant velocity in a straight line. The acceleration is proportional to the force and in the direction of the force.
Orbital motion is a continuous acceleration.
He 'invented' the force of gravity to explain the fall of an apple to earth, the motions of the Moon and planets, etc. With the law of gravitation one could predict the future positions of planets to great accuracy. When much later the orbit of Uranus showed it departing from the predicted one, it was supposed that an even more distant planet was pulling Uranus out of its predicted orbit. This was a triumph for gravitation. The orbit of Mercury, however, was not predicted correctly by Newton's law of gravitation.