We report observations of the lunar helium exosphere made between December 29, 2011, and January 26, 2012, with the Lyman Alpha Mapping Project (LAMP) ultraviolet spectrograph on NASA's Lunar Reconnaissance Orbiter Mission (LRO). The observations were made of resonantly scattered He I 584 from illuminated atmosphere against the dark lunar surface on the dawn side of the terminator. We find no or little variation of the derived surface He density with latitude but day-to-day variations that likely reflect variations in the solar wind alpha flux. The 5-day passage of the Moon through the Earth's magnetotail results in a factor of two decrease in surface density, which is well explained by model simulations.
@article{arxiv.1209.3274,
title = {Temporal Variability of Lunar Exospheric Helium During January 2012 from LRO/LAMP},
author = {Paul D. Feldman and Dana M. Hurley and Kurt D. Retherford and G. Randall Gladstone and S. Alan Stern and Wayne Pryor and Joel Wm. Parker and David E. Kaufmann and Michael W. Davis and Maarten Versteeg and LAMP team},
journal= {arXiv preprint arXiv:1209.3274},
year = {2015}
}
Comments
21 pages, 5 figures, 3 supplementary figures, accepted for publication in Icarus