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Detections of lunar exospheric ions by the LADEE neutral mass spectrometer
Journal article   Peer reviewed

Detections of lunar exospheric ions by the LADEE neutral mass spectrometer

J. S Halekas, M Benna, P. R Mahaffy, R. C Elphic, A. R Poppe and G. T Delory
Geophysical research letters, Vol.42(13), pp.5162-5169
07/16/2015
DOI: 10.1002/2015GL064746

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Abstract

The Lunar Atmosphere and Dust Environment Explorer (LADEE) Neutral Mass Spectrometer (NMS), operating in ion mode, provides sensitive detections of ions from the lunar exosphere. By analyzing ion‐mode data from the entire mission, utilizing Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) plasma and magnetic field measurements to organize NMS data and eliminate background sources, we identify highly significant detections of lunar ions at mass per charge of 2, 4, 12, 20, 28, 39, and 40, moderately significant detections at 14 and 23, and weak detections at 24, 25, and 36. Unlike many previous observations of Moon‐derived ions, an outward pointing viewing geometry ensures that these ions originate from the exosphere, rather than directly from the surface. For species with known neutral distributions, inferred ion production rates appear consistent with expectations for both magnitude and spatial distribution, assuming photoionization as the predominant source mechanism. Unexpected signals at mass per charge 12 and 28 suggest the presence of a significant exospheric population of carbon‐bearing molecules. Key Points The LADEE neutral mass spectrometer detected exospheric ions at the Moon NMS detected H2+, He+, C+, Ne+, Na+, K+, Ar+, and an ambiguous 28 amu ion Simultaneous plasma data are critical for interpreting NMS ion measurements
 exosphere Moon plasma

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