|The Diviner Lunar Radiometer Experiment on NASA’s Lunar Reconnaissance Orbiter (LRO) has been systematically mapping the global thermal state of the Moon since July of 2009. The instrument has acquired solar reflectance and mid-infrared radiance measurements in nine spectral channels spanning a wavelength range from 0.3 to 400 μm (Paige et al., 2010a). With nearly five years of data, the density of observations both spatially and in localtime is high enough that global diurnal temperatures can be adequately resolved to create global maps of surface temperatures. Nadir observations of radiance from the 7 infrared spectral channels are used to derive bolometric brightness temperatures, a measure of the spectrally integrated flux of infrared radiation emerging from the surface (Paige et al., 2010b). For the purposes of quantifying the overall heat balance of the surface and comparing with available models, the bolometric brightness temperature is the most fundamental and interpretable measurable quantity. With the diurnal temperatures determined for each 0.5 degree of binned data we create instantaneous global maps of surface temperatures for a given subsolar point.
These systematic observations of the global thermal state of the Moon and its diurnal variability provides the ability to characterize the surface energy balance and develop an understanding of how the lunar regolith stores and exchanges heat. The highly insulating nature of the surface, the lack of an appreciable atmosphere to buffer surface temperatures, and slow rotation, result in an extremely complex thermal environment, especially when illumination angles are low such as in the vicinity of the dawn and dusk terminators and at high latitudes and the polar regions, where topography dominates the surface temperatures. Temperatures can vary by >100 K between shadowed and sunward facing slopes down to the smallest length scales resolved. In addition to topographic effects, daytime temperatures, which are in near-equilibrium with the solar flux, are influenced by radiative properties of the surface. Nighttime temperatures however are determined by the radiation of sensible heat stored in the subsurface during the day and therefore are sensitive to the thermophysical properties of the regolith (Bandfield et al., 2011, Vasavada et al., 2012).
Paige, D. A., et al. (2010a) The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment, Space Sci. Rev., 150, 125-160.
Paige, D. A., et al. (2010b) Diviner Lunar Radiometer observations of cold traps in the Moon’s south polar region, Science, 330, 479-482.
Vasavada, A. R., et al. (2012) Lunar equatorial surface temperatures and regolith properties from the Diviner Lunar Radiometer Experiment, J. Geophys. Res., 117, E00H18, doi:10.1029/2011JE00398.