| The thermal response of the surface layer of an airless planetary body to sunlight is a result of the complex interplay of a number of thermophysical regolith properties. Properties such as grain size, bulk density, porosity, thermal conductivity, and rock abundance all play a role in the thermal behavior of a regolith. Penetration of sunlight below the surface and near-surface thermal emission can also effect regolith subsurface temperatures and emitted fluxes. I have done three investigations of the effects of regolith properties on thermal behavior of the surface layers of airless planetary bodies. In each investigation, I have included additional physics in a standard one-dimensional thermal-diffusion model.;In the first investigation, I modified the diurnal thermal-diffusion model to include the temperature-dependence of specific heat and thermal conductivity for the lunar regolith. I then used laboratory data taken from the literature to determine the effects of grain size, bulk density (or porosity), thermal conductivity, and rock abundance on lunar surface temperatures. Variations in rock abundance are by far the strongest contributors to thermal inertias derived from nighttime lunar thermal infrared observations.;In the second investigation, I constrained the magnitude of the solid-state greenhouse effect for each of the icy Galilean satellites. In icy regoliths, sunlight can penetrate below the surface, potentially affecting subsurface temperatures and thermal emission. Once again, I modified a diurnal standard thermal diffusion model, this time to include subsurface insolation. Using surface temperature data of Europa, Ganymede, and Callisto from the Voyager spacecraft, I found that the maximum subsurface heating could occur on Europa, with no more than a 10 K elevation in mean subsurface temperatures.;In the third investigation, I examined the impact of near-surface thermal gradients on lunar subsurface temperatures and thermal emission. I modified the thermal model from my first investigation to include both subsurface insolation and thermal emission from the near-surface. My model produced significant subsurface heating, with subsurface temperatures strikingly similar to those observed by the Apollo 15 and 17 heat flow experiments. I also found that near-surface thermal gradients can have a significant impact on IR emission, and should be considered when deriving thermal inertia from lunar infrared observations. |
