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Structure and Composition of the Distant Lunar Exosphere: Constraints from ARTEMIS Observations of Ion Acceleration in Time-Varying FieldsBy analyzing the trajectories of ionized constituents of the lunar exosphere in time-varying electromagnetic fields, we can place constraints on the composition, structure, and dynamics of the lunar exosphere. Heavy ions travel slower than light ions in the same fields, so by observing the lag between field rotations and the response of ions from the lunar exosphere, we can place constraints on the composition of the ions. Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) provides an ideal platform to utilize such an analysis, since its two-probe vantage allows precise timing of the propagation of field discontinuities in the solar wind, and its sensitive plasma instruments can detect the ion response. We demonstrate the utility of this technique by using fully time-dependent charged particle tracing to analyze several minutes of ion observations taken by the two ARTEMIS probes ~3000-5000 km above the dusk terminator on 25 January 2014. The observations from this time period allow us to reach several interesting conclusions. The ion production at altitudes of a few hundred kilometers above the sunlit surface of the Moon has an unexpectedly significant contribution from species with masses of 40 amu or greater. The inferred distribution of the neutral source population has a large scale height, suggesting that micrometeorite impact vaporization and/or sputtering play an important role in the production of neutrals from the surface. Our observations also suggest an asymmetry in ion production, consistent with either a compositional variation in neutral vapor production or a local reduction in solar wind sputtering in magnetic regions of the surface.
Document ID
20170002509
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Halekas, J. S.
(Iowa Univ. Iowa City, IA, United States)
Poppe, A. R.
(California Univ. Berkeley, CA, United States)
Farrell, W. M.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
McFadden, J. P.
(California Univ. Berkeley, CA, United States)
Date Acquired
March 23, 2017
Publication Date
June 30, 2016
Publication Information
Publication: Journal of Geophysical Research: Planets
Publisher: WILEY
Volume: 121
Issue: 6
ISSN: 2169-9097
Subject Category
Lunar And Planetary Science And Exploration
Report/Patent Number
GSFC-E-DAA-TN40281
Funding Number(s)
CONTRACT_GRANT: NAS5-02099
CONTRACT_GRANT: NNX13AJ97G
Distribution Limits
Public
Copyright
Other
Keywords
Moon
exosphere
ion acceleration
pickup ions

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