Friday, September 21, 2012

Temporal Variability of Lunar Exospheric Helium During January 2012 from LRO/LAMP

Depicted here are atmospheric emission spectra (black) obtained by LAMP on two dates in late 2011, in units of Rayleighs per angstrom. Each panel’s black line is the spectrum obtained by LAMP when its spectrograph slit was placed 83 deg from the nadir, just above the lunar limb. The red line in each panel is the background spectrum obtained close in time by observing the same patch of sky when it is at the zenith, where any contribution from the lunar atmosphere is minimized. The blue line in each panel is the difference spectrum obtained by subtracting the background from the limb spectrum, revealing native lunar atmospheric emission from He I at 584 Å. 1-sigma error bars are depicted on each curve every 4th spectral point, for reference. From "First atmospheric helium detection by LRO LAMP," Stern, SWrI; et al, (2012).
Feldman, et al.
arXiv 1209.3274
Johns Hopkins, APL, SWrI, Central Arizona College

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 l584 from illuminated atmosphere against the dark lunar surface on the dawn side of the terminator. We find little or no 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.
Read the research, HERE

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