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Title:
Laboratory Visible to Far-Infrared Measurements in Support of the 2009 LRO Diviner Lunar Radiometer Compositional Investigation
Authors:
Greenhagen, B. T.; Paige, D. A.; Bowles, N. E.; Thomas, I.
Affiliation:
AA(University of California, Los Angeles - Dept of Earth and Space Sciences, 595 Charles Young Drive East Box 951567, Los Angeles, CA 90095-1567, ; ), AB(University of California, Los Angeles - Dept of Earth and Space Sciences, 595 Charles Young Drive East Box 951567, Los Angeles, CA 90095-1567, ; ), AC(University of Oxford - Department of Physics, Clarendon Laboratory Parks Road, Oxford, OX1 3PU, United Kingdom ; ), AD(University of Oxford - Department of Physics, Clarendon Laboratory Parks Road, Oxford, OX1 3PU, United Kingdom ; )
Publication:
American Geophysical Union, Fall Meeting 2008, abstract #P31B-1420
Publication Date:
12/2008
Origin:
AGU
AGU Keywords:
3630 Experimental mineralogy and petrology, 3934 Optical, infrared, and Raman spectroscopy, 5470 Surface materials and properties, 6250 Moon (1221), 6297 Instruments and techniques
Bibliographic Code:
2008AGUFM.P31B1420G

Abstract

We measured reflectance spectra of common lunar minerals spanning wavelengths from the visible to the far-infrared. These measurements provided critical data related to spectral variability of lunar minerals relevant to the Diviner lunar radiometer Compositional Investigation. Diviner will launch in early 2009 onboard the Lunar Reconnaissance Orbiter (LRO). Diviner is a nine-channel radiometer designed to study the thermal-physical and compositional properties of the lunar surface. Diviner has two solar channels (0.35- 2.8 μm; high / low sensitivity), three '8-micron' channels (7.55-8.05, 8.10-8.40, and 8.40-8.70 μm), and four thermal channels (13-23, 25-41, 50-100, 100-200 μm). The Diviner Compositional Investigation will use the 8-micron channels to determine the location of the Christiansen Feature, which is a good compositional indicator. The Christiansen Feature has a systematic behavior for silicates and shifts to longer wavelengths with increasing polymerization of the Si-04 tetrahedra. Therefore, the Christiansen Feature is located at shorter wavelengths for more felsic materials and longer wavelengths for more mafic materials. Additional compositional constraints will be gained using bulk solar albedo from solar channel data and spectral variation of thermal channels data. Even at Diviner's far- infrared spectral resolution, differences between mineral spectra are evident. It was important to have competent laboratory spectra measured across all Diviner-sensitive wavelengths. The spectra presented were measured on a Bruker IFS66/V Fourier transform infrared spectrometer at the University of Oxford Atmospheric, Oceanic, and Planetary Physics Laboratory. In order to cover Diviner's 0.3-200 micron response, we used three sources (quartz-tungsten, Glowbar, and mercury-arc) and several beam splitters. The measurements included the most common lunar minerals quartz, anorthite, enstatite, augite, forsterite, fayalite, and ilmenite and additional minor minerals. The samples were crushed and dry-sieved to different grain size seperates (< 30, 30-64, 64-120, and 120-450 μm). These minerals were also mixed into several analog lunar rock compositions. The location of the Christiansen Feature for 64-120 μm seperates in low vacuum was measured as follows: quartz, 7.38 μm; anorthite, 8.03 μm; enstatite, 8.38 μm; augite, 8.42 μm; forsterite, 8.88 μm; and fayalite, 9.38 μm. It was observed that the shape of Christiansen Feature changed and the location shifted slightly with changes in grain size and sample camber pressure. Some minerals also showed variations in solar albedo with grain size. Understanding spectral variations in common lunar minerals is critical to the success of the Diviner Compositional Investigation. These measurements represent an important first step. Future studies will expand the measurements to include a simulated lunar environment (i.e. emission measurements in vacuum with a cold back shield).
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