Question

Is there an explanation for this 'quirk' of Newtonian gravity?

Answer 1

If you have the Sun (marked '1'), then all points along the circle (assume from now on that all solar satellites in this example have the same mass) would experience the same gravitational pull. But...

Answer 2

Consider 2 objects of the same mass, but different densities.. The inner parts (y on the diagram) will experience more force than the outer parts (labelled here x). However, for planet A, y/x is smaller than planet B's y/x, so surely it would experience less force?

Answer 3

Essentially, for the smaller object, z is less proportionally to its diameter than for A. So, if this is right, it shows that Newton's idea of a centre of mass is just a (incredibly accurate) rule of thumb.