When this parameter is defined to a non-zero value , the smoothing length for the evaluation over the mesh of the potential arising from each planet is , where is the Hill sphere radius of the planet, defined by:
where and are respectively the mass of the planet and the mass
of the central object, and where is the planet's semi-major axis.
This same Hill radius fraction applies to all planets simultaneously. The use of this parameter is mutually exclusive with the use of