A pure rock planet with no atmosphere has a spin period of 24 hours. Consider a patch of the planet's surface at the equator. At the surface, there is a diurnal (daily) temperature variation of T as the patch alternates between 12 hours of daylight and 12 hours of night. Sufficiently far below the surface, at depths d > dskin, diurnal temperature vari- ations are T. In other words, rock sufficiently deep in the planet's interior, below the "thermal skin depth" dskin, cannot tell whether it is day or night. Make a rough, order-of-magnitude, numerical estimate for dskin. Explain your reasoning and specify the units of your answer. Hint: rocks and turkeys can be approximated as being made of the same material, i.e. having the same thermal properties