A diurnal study of lunar topography to determine regolith temperature contributions to the inference of hydrogen volatiles using epithermal neutrons from the Lunar Exploration Neutron Detector (LEND).

Friday, 19 December 2014
Timothy P McClanahan1, Igor G. Mitrofanov2, William V Boynton3, Gordon Chin4, Larry G. Evans5, Richard D Starr6, Timothy A Livengood7, Maxim L Litvak2, Anton B. Sanin2, Joseph Murray8, Ann M Parsons1, Jao Jiang Su8, Julia Bodnarik3, Karl Harshman3 and Roald Sagdeev8, (1)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (2)Space Research Institute RAS, Moscow, Russia, (3)Univ Arizona, Tucson, AZ, United States, (4)NASA Goddard Space Flight Center, Code 693, Greenbelt, MD, United States, (5)Computer Sciences Corporation, Stennis Space Center, MS, United States, (6)Catholic University of America, Washington, DC, United States, (7)University of Maryland College Park, College Park, MD, United States, (8)University of Maryland College Park, Physics, College Park, MD, United States
In this research we investigate lunar volatiles in the Moon’s southern latitudes under diurnal conditions using five years of accumulated epithermal neutron observations by the Lunar Reconnaissance Orbiter’s Lunar Exploration Neutron Detector. The primary objective of this research is to determine the spatial extent and magnitude of a possible regolith temperature contribution to the Moon's epithermal leakage flux as a function of topography. Ongoing research has suggested that there exists a widespread preferential bias in hydrogen concentrations towards the Moon’s poleward-facing slopes as evidenced by a localized 1-2% suppression of the lunar epithermal leakage flux relative to equivalent equator-facing slopes (McClahanan et al., Under Review 2014). Monte Carlo neutron modeling results by (Lawson et al., 2000; Little et al. 2002) found that the epithermal neutron leakage flux may be slightly enhanced ~1% with regolith temperature in lunar conditions. Contrasting temperature conditions on poleward-facing and equator-facing slopes may at least partially explain the observation of biased concentrations of hydrogen towards poleward-facing slopes. To isolate any temperature contribution, LEND night observations are mapped and correlated with temperature maps from LRO's Diviner radiometer and terrain and illumination models derived from the Lunar Observing Laser Altimeter. Night and day results are contrasted to illustrate both the magitude and latitude extent of putative temperature effects and spatial hydrogen distributions.