On the observed clustering of major bodies in solar and extrasolar subsystems.

Major (exo)planetary and satellite bodies seem to concentrate at intermediate areas of the radial distributions of all the objects present in each (sub)system. We prove rigorously that the secular evolution of (exo)planets and satellites necessarily results in the observed intermediate accumulation of the massive objects in all such subsystems. We quantify a "middle" as the mean of mean motions (orbital angular velocities) of three or more massive objects involved. Orbital evolution is expected to be halted or severely diminished when the survivors settle near mean-motion resonances and substantial angular-momentum transfer between bodies ceases to occur (gravitational Landau damping). The dynamics is opposite in direction to what has been theorized for viscous and magnetized accretion disks in which gas spreads out and away from either side of any conceivable intermediate area. The results are bound to change the way we think about planet and moon formation and evolution.