Introduction

The temperature distribution in the regolith of a body of the solar system is important for several reasons. First, the mean temperature is one of the fundamental properties of an object; second, the regolith is the part of the planet studied by remote-sensing methods; and third, the temperature distribution in the upper layers constitutes the boundary condition for thermal models of the deeper interior. The temperatures in the regolith are governed by three energy-transport processes that interact within the medium: visible and near-IR solar radiation, thermal radiation, and heat conduction. However, most models treat the energy as being carried entirely by thermal conduction inside the medium, the interaction with radiation being treated only as a boundary condition. In this chapter all three processes occurring in the medium are treated simultaneously. In doing so it will be seen that radiative conductivity of heat and the solid-state greenhouse effect appear intrinsically without any ad hoc assumptions.

In Section 16.2 the time-dependent, one-dimensional radiative and heat conduction equations are introduced. The time-independent equations are solved analytically for two important cases: a layer of isotropically scattering particles heated from below and radiating into a vacuum, simulating conditions often used in laboratory IR and thermal measurements, and a semi-infinite medium of isotropic scatterers heated by incident visible light and radiating into a vacuum, simulating a planetary regolith in equilibrium with sunlight. In the final section some time-dependent problems are discussed briefly.