LRO Diviner Radiometer and the Apollo 15 Heat Flow Experiment
Abstract
A synergistic relationship has grown out of incoming data from the Diviner infrared radiometer aboard LRO, and measurements from the Apollo 15 and 17 heat flow experiments. Here we look at the 3.5 year surface and subsurface temperatures from the Apollo 15 mission as both a calibration point for Diviner and as a guide for extending surface thermal properties models into the subsurface. Whereas Diviner’s strength is in global surface properties, the Apollo 15 data (from NSSDC: PSPG-00752) recorded subsurface temperatures within the top 2 meters of the regolith.
The goal is to use an Apollo-based conductivity and density model as a base for global lunar regolith conditions. A model confirmed both with surface and subsurface temperatures from Apollo 15 will be a reliable calibration point for Diviner. Thermal variations at other locations can be fixed to specific changes in the local subsurface regolith structure and associated thermal properties. Here we examine the current radiometric surface temperatures at the Apollo 15 landing site derived from Diviner data, then apply our thermal model to USGS topography data sets (10m and 50m resolution; Rosiek, 2009) to correlate measured temperatures with near surface thermal properties. This same model will be illuminated using ephemeris conditions appropriate to the 1971-74 Apollo 15 heat flow experiment. Beginning with previously published thermal property models (Vasavada et al 1999, Keihm and Langseth 1975, Langseth and Keihm 1976, Keihm 1984), we will model the regolith and thermal probe to recreate seasonal, diurnal and other transient thermal behavior measured by the Apollo heat flow experiment. This model should allow for more confidence in using surface temperatures measured by Diviner to infer regolith structure at depth. Ray tracing thermal models developed for Diviner can include effects of topography and orbital cycles that have led some to challenge the validity of conclusions drawn from the Apollo data sets (Saito et al 2007, 2008). Shallow Apollo data show clear signs of shunting of heat down the borestem of the thermal probe at the onset of the lunation cycle, requiring 2 or 3D models. The thermal probe also showed a long term drift postulated to be caused by either alteration of surface conditions by the Apollo astronauts (Langseth et al 1976) or the 18.6 year component of the lunar orbit (Saito 2008). An overarching explanation of these inconsistencies should bolster confidence in an Apollo based thermal model and heat flow results as well as provide a base for modeling diffusive movement of volatiles through the near surface regolith in polar environments. [1] Keihm S. and Langseth (1975) Icarus 24, 211. [2] Keihm (1984) Icarus 60, 568. [3] Langseth, M. G. et al. (1976) Proc. Lunar Sci. Conf., 7th, 3143. [4] Courtesy Rosiek M., USGS Astrogeology Science Center, http://astrogeology.usgs.gov [5] Saito, Y. (2007) Proc. 38th Lunar Planet. Sci. Conf., 2197. [6] Saito, Y. (2008) Proc. 39th Lunar Planet. Sci. Conf., 1663. [7] Vasavada A. et al (1999) Icarus 141, 179.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.U31A0022S
- Keywords:
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- 5410 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Composition;
- 5418 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Heat flow;
- 5460 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Physical properties of materials;
- 6250 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Moon