Explain the preferentially low masses of innermost and outermost planets

Determine whether the systematically lower masses of the innermost and outermost planets in the simulated planetary systems arise from a narrower range of planetary-embryo mass within the Hill spheres of the innermost and outermost protoplanets.

Background

The simulations show that the innermost planet is the lightest planet in approximately 44% of systems, and the outermost planet is likewise the lightest in approximately 44% of systems. These frequencies exceed the values expected from random ordering of planet masses.

The authors do not establish the physical origin of this mass ordering; they explicitly present the restricted range of embryo masses within the boundary protoplanets’ Hill spheres as a hypothesis requiring confirmation.