Interpreting LRO Diviner surface temperatures: Modeling three-dimensional lunar regolith thermophysical properties

Details Interpreting LRO Diviner surface temperatures: Modeling three-dimensional lunar regolith thermophysical properties Interpreting LRO Diviner surface temperatures: Modeling three-dimensional lunar regolith thermophysical properties

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51c1445w&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P51C-1445

Physics

[5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6250] Planetary Sciences: Solar System Objects / Moon

Scientific paper

The Diviner Lunar Radiometer Experiment on NASA's Lunar Reconnaissance Orbiter has been mapping the global thermal state of the Moon since July of 2009. The instrument has acquired solar reflectance and thermal emission data in nine spectral channels spanning a wavelength range from 0.3 to 400 microns [1] revealing the extreme nature of the lunar thermal environment. Superposed on the large-scale trends due to latitude, time of day, and season, the surface temperature of the Moon can exhibit extreme spatial variations at length scales all the way down to that of the diurnal thermal skin depth (˜10 cm) due to the low thermal conductivity of the bulk of the regolith, the lack of an appreciable atmosphere, and the effects of slopes and shadowing [2]. Further, surface temperatures are highly sensitive to the thermophysical properties within the first few meters of the surface and thus spatial variations in density, thermal conductivity, heat capacity, albedo, and emissivity, will have an influence. This significantly complicates the interpretation of lunar thermal observations and thermal model results. To aid in our interpretation of Diviner data and model derived results, we are developing a 3-diminsional regolith model to better understand how variations both vertically and laterally of the thermophysical properties of the lunar regolith can affect Diviner observations. This extends previous 1-dimisional modeling efforts which included vertical layering [3] to now capture lateral variability in regolith properties which, in the lunar environment, can result in extreme thermal gradients over short length scales (10’s cm). The initial application of the model is to explore the sensitivity of the surface temperature throughout the diurnal cycle to rocks in the regolith. With no appreciable atmosphere to buffer surface temperatures, the nighttime environment is characterized by extreme cold with the sensible heat stored in the subsurface during the day being the only heat source to balance the loss of thermal radiation to space during the long lunar night. As a result, surface temperatures are sensitive to rocks as they can remain warmer than the surrounding regolith throughout the Lunar night with 1 m rocks remaining as much as ˜90 K warmer [1][4]. Our 3D finite element model is flexible in that we can explore an arbitrary number of nodes and length scales with arbitrary geometries of embedded thermophysical properties to represent a rock as well as vertical layering to capture the temperature dependent conductivity in the top few centimeters of the regolith. Given a diurnal solar forcing function at the surface we then can use this model to develop an understanding of the size range of rocks that the Diviner instrument should be sensitive to and characterize how rocks may influence the observations. References: [1] Paige, D. A. et. al. (2009) Space Sci. Rev., DOI: 10.1007/s11214-009-9529-2 [2] Paige, D. A. et. al. (2010) 41st LPSC, 2267 [3] Vasavada, A. R. et al. (1999) Icarus, 141, 179-193 [4] Bandfield, J. L. et al. (2010) 41st LPSC, 2012.

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