There is an altitude above every planet where a moon can orbit forevermore. In millions of miles of ups and downs, there is one narrow passageway of permanence. If a moon can reach this groove, it will never crash down like masonry nor drift away like a mood; it will be inalienable; it will circle its planet at the exact speed that the planet rotates, always over one site, like the Badlands or Brazzaville or the Great Red Spot, so that the planet neither drags the moon faster nor slows it down. Moons not locked into this synchronous orbit are either being perturbed up or down.