δ = (\frac{R_{p}}{R_{s}} )^{2}

θ ≃ \frac{R_{s}}{a}

\frac{2θ}{2π} = \frac{T}{P}

\frac{T}{P} = \frac{R_{s}}{πa}

P^{2} = \frac{4π^{2}}{\frac{4}{3}πGρ_{s}} (\frac{a^{3}}{R_{s}^{3}} )

P^{2} = \frac{4π^{2}}{\frac{4}{3}πGρ_{s}} (\frac{P^{3}}{π^{3}T^{3}} )