 1. What physically retains the planets in orbits around the Sun and their satellites in orbit around them? Newton's answer — inverse-square gravity, one in kind with everyday terrestrial gravity — turned on a largely suppressed failure to account for more than half of the precession of the lunar orbit, it tacitly assumed interaction between the Sun and Jupiter and the other individual planets, and it raised unanswered questions about whether the perihelia of the planetary orbits do or do not precess.