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Sources of Sodium in the Lunar Exosphere: Modeling Using Ground-Based Observations of Sodium Emission and Spacecraft Data of the PlasmaObservations of the equatorial lunar sodium emission are examined to quantify the effect of precipitating ions on source rates for the Moon's exospheric volatile species. Using a model of exospheric sodium transport under lunar gravity forces, the measured emission intensity is normalized to a constant lunar phase angle to minimize the effect of different viewing geometries. Daily averages of the solar Lyman alpha flux and ion flux are used as the input variables for photon-stimulated desorption (PSD) and ion sputtering, respectively, while impact vaporization due to the micrometeoritic influx is assumed constant. Additionally, a proxy term proportional to both the Lyman alpha and to the ion flux is introduced to assess the importance of ion-enhanced diffusion and/or chemical sputtering. The combination of particle transport and constrained regression models demonstrates that, assuming sputtering yields that are typical of protons incident on lunar soils, the primary effect of ion impact on the surface of the Moon is not direct sputtering but rather an enhancement of the PSD efficiency. It is inferred that the ion-induced effects must double the PSD efficiency for flux typical of the solar wind at 1 AU. The enhancement in relative efficiency of PSD due to the bombardment of the lunar surface by the plasma sheet ions during passages through the Earth's magnetotail is shown to be approximately two times higher than when it is due to solar wind ions. This leads to the conclusion that the priming of the surface is more efficiently carried out by the energetic plasma sheet ions.
Document ID
20110013535
Document Type
Reprint (Version printed in journal)
Authors
Sarantos, Menelaos (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Killen, Rosemary M. (Maryland Univ. College Park, MD, United States)
Sharma, A. Surjalal (Maryland Univ. College Park, MD, United States)
Slavin, James A. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 25, 2013
Publication Date
August 6, 2009
Publication Information
Publication: Icarus
Volume: 205
Issue: 2
ISSN: 0019-1035
Subject Category
Lunar and Planetary Science and Exploration
Report/Patent Number
GSFC.JA.4597.2011
Funding Number(s)
CONTRACT_GRANT: NNX08AY95G
Distribution Limits
Public
Copyright
Other