$\quad \mathrm{T}^{2} \propto \mathrm{R}^{3}$ $$ \begin{aligned} & \left(\frac{\mathrm{T}_{\mathrm{m}}}{\mathrm{~T}_{\mathrm{s}}}\right)^{2}=\left(\frac{\mathrm{R}}{\mathrm{R} / 9}\right)^{3} \\ & \frac{\mathrm{~T}_{\mathrm{m}}}{\mathrm{~T}_{\mathrm{s}}}=(3)^{3} \\ & \Rightarrow \mathrm{~T}_{\mathrm{s}}=\left(\frac{27}{27}\right)=1 \text { day } \end{aligned} $$