Hendrix, Amanda - REGIONAL VARIATIONS IN FUV LUNAR SIGNATURES

Abstract: 
The Lunar Reconnaissance Orbiter (LRO) is currently in orbit at the Moon. The Lyman Alpha Mapping Project (LAMP) onboard LRO has been making measurements of the lunar nightside, dayside and atmosphere since September 2009. We report here on recent work analyzing LAMP dayside data, focusing on weathering and hydration effects in mature vs. immature terrains, including swirls.
The LAMP instrument [1] is a photon-counting imaging spectrograph. The entire passband is 57–196 nm, in the far-UV (FUV) spectral region. For dayside measurements, the instrument is operated in “pinhole” mode, with the aperture reduced by a factor of 736. The instrument was usually nadir-pointed in LRO’s characteristic 50-km lunar orbit of the prime mission and provided ~500 m resolution.  Approximately once per month LRO flies over any particular region; and although LAMP halts acquistion of dayside data when at high phase angles, there are numerous sets of spectra of each region at differing geometries; the emission angle is small while the incidence angle is larger and varies depending on the beta angle of the orbit. To determine the lunar FUV reflectance, we divide the LAMP data from each latitude bin by the full-disk solar spectrum from SORCE SOLSTICE [2], taken for the day of each observation and convolved to agree with the LAMP resolution and line spread function.
The FUV hosts a strong H2O absorption edge near 165 nm, allowing LAMP to study hydration on the Moon [3]. Past analyses of LAMP dayside data (e.g. [3]) have shown that the measurement of spectral slopes in the 164-173 nm range is an indicator of hydration, while spectral slopes in the 175-190 nm region are insensitive to hydration but good indicators of weathering and composition.
Here we use this spectral slope information to study hydration and weathering effects in swirls regions (Reiner Gamma, Mare Ingenii, Gerasimovich, Descartes highlands) and in immature regions (e.g. after [4]).

References: [1] Gladstone, G. R. et al. (2010) SSR, 150, 161-181. [2] McClintock et al. (2000) Proc. SPIE Earth Obs. Syst., 4135, 225–234.  [3] Hendrix et al. (2012) JGR, 117, E12001, doi:10.1029/2012JE004252. [4] Lucey, P. G. et al. (2000) JGR, 105, 20377.