bedo of the Moon at far-UV wavelength region is 'in- verted' compared to ... where the far-UV albedo reversal of the Moon's mare and highlands region occurs.
45th Lunar and Planetary Science Conference (2014)
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LRO Lyman Alpha Mapping Project (LAMP) Investigation of the Lunar Albedo Far-UV Spectral Inversion. C. M. Seifert1,2 , K. E. Mandt1, K. D. Retherford1. T. K. Greathouse1, A. R. Hendrix3, A. F. Egan4, G. R. Gladstone1, P. D. Feldman5, C. Grava1, P. F. Miles1; 1Southwest Research Institute, Space Science & Engineering, PO Drawer 28510, 2St. Mary's University, San Antonio, TX 3Planetary Science Institute, Los Angeles, CA, 4Southwest Research Institute, Boulder, CO, 5Johns Hopkins University, Baltimore, MD. Introduction: One of the main findings of the Apollo 17 UV Spectrometer experiment is that the albedo of the Moon at far-UV wavelength region is 'inverted' compared to expectations from the more common visible light imagery [1]. This spectral inversion is prevalent in lab measurements of returned lunar soils but is absent in crushed rock powders [2], which implies a relation to space weathering other surface alteration processes [3]. Asteroids and likely other solid bodies in the solar system lacking atmospheres exhibit similar spectral trends at far-UV wavelengths (e.g., 100-200 nm) [4]. We investigate the wavelength where the far-UV albedo reversal of the Moon's mare and highlands region occurs. By using data obtained from the Lyman Alpha Mapping Project (LAMP) instrument on the Lunar Reconnaissance Orbiter (LRO) spacecraft [5] we identify a distinct inverse relation between the far-UV albedo and the visible albedo of the Moon (Figure 1). The Moon is divided into two distinct units, the brighter highlands and the darker mare regions. The mare regions which are now filled with iron were defined by past volcanic eruptions and are much younger then the brighter highlands. It is the abundance of anorthosite that gives the hilly portions of the Moon its bright color in stark contrast to the Mare regions. By comparing mare and highland regions measured at several wavelengths within the 57-196 nm spectral range of the LAMP instrument we plan to obtain a deeper understanding of the space weathering and surface altering processes that lead to the spectral inversion signature. LAMP Methodology:The LAMP instrument is an imaging spectrograph that measures ultraviolet surface reflectance using illumination by: 1) the Sun when LRO is on the dayside, and 2) the interplanetary medium and UV-starlight when on the nightside and/or when over permanently shaded regions (PSRs) [6,7]. The LAMP albedo maps provide sub-km resolution on the lunar surface and now cover both polar and equatorial regions [8]. Future Work: We are currently developing maps that divide the global LAMP maps into finer spectral bins to pinpoint the wavelength where the spectral inversion occurs. Maps of spectral slopes are determined from these products and our recent progress in identify-
ing regions with relatively blue and red spectral slopes will be reported.
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Figure 1: LROC-WAC western equatorial hemisphere map (top) and LAMP Lyman-α nightside brightness (bottom). References: [1] Lucke R. L. et. al. (1976). Astron. J. 81, 12. [2] Wagner, J.K. et. al.(1987): Icarus 69, 14-28. [3]Hapke. B.(2001). JGR, 106, E5, 10,309- 10,073. [4] Hendrix, A. Vilas, F. (2006) The Astron. J., 0:13961404. [5] Gladstone, G. R. et. al. (2010). Space Sci. Rev., 150, 161-181. [6] Hendrix, A. et al. (2012). JGR, 117, E12001.[7] Gladstone, G. R. et al. (2012). Geophys. Res., 117, E00H04,[8] Retherford K. D. et. al. (2014). LPSC Meeting.
