A Microphysical Thermal Model for the Lunar Regolith: Investigating the Latitudinal Dependence of Regolith Properties

Abstract

Abstract The microphysical structure of the lunar regolith provides information on the geologic history of the Moon. We used remote sensing measurements of thermal emission and a thermophysical model to determine the microphysical properties of the lunar regolith. We expand upon previous investigations by developing a microphysical thermal model, which more directly simulates regolith properties, such as grain size and volume filling factor. The modeled temperatures are matched with surface temperatures measured by the Diviner Lunar Radiometer Experiment on board the Lunar Reconnaissance Orbiter. The maria and highlands are investigated separately and characterized in the model by a difference in albedo and grain density. Within the stratification model, we identified the turnover pressure as a critical parameter, and with a lower absolute calibration of this parameter, the modeled regolith temperatures are best described by the bulk densities and mean grain sizes obtained from returned Apollo samples. We then study the latitudinal dependence of regolith properties in the highlands up to latitude. For a higher absolute calibration of the turnover pressure, we identified one combination of regolith properties at the lunar equator that can fit all latitudes reasonably well. For other sets of regolith properties and especially the lower calibration of the turnover pressure, we find that a variation of the solar incidence‐dependent albedo can reduce the initially observed latitudinal gradient between model and Diviner measurements significantly. A better match can be achieved by a variation in intrinsic regolith properties with a decrease in bulk density with increasing latitude.

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