Mutual Hill radius ($R_{H,m}=\frac{a_1+a_2}{2}[(M_1+M_2)/(3M_{\star }){]}^{1/3}$)

A scale for the combined gravitational influence of two small orbiting bodies relative to their common host star. It is often used to express the separation of neighboring planetary embryos. For equal masses and nearly equal orbital radii it exceeds the individual Hill radius by $2^{1/3}$.