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Stair-Step Particle Flux Spectra on the Lunar Surface: Evidence for Nonmonotonic Potentials?We present examples of unusual "stair‐step" differential flux spectra observed by the Apollo 14 Suprathermal Ion Detector Experiment on the lunar dayside surface in Earth's magnetotail. These spectra exhibit a relatively constant differential flux below some cutoff energy and then drop off precipitously, by about an order of magnitude or more, at higher energies. We propose that these spectra result from photoions accelerated on the lunar dayside by nonmonotonic potentials (i.e.,potentials that do not decay to zero monotonically) and present a model for the expected differential flux. The energy of the cutoff and the magnitude of the differential flux are related to the properties of the local space environment and are consistent with the observed flux spectra. If this interpretation is correct, these surface‐based ion observations provide a unique perspective that both complements and enhances the conclusions obtained by remote‐sensing orbiter observations on the Moon's exospheric and electrostatic properties.
Document ID
20170000994
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Collier, Michael R. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Newheart, Anastasia (Saint Mary's Coll. of Maryland Saint Mary's City, MD, United States)
Poppe, Andrew R. (California Univ. Berkeley, CA, United States)
Hills, H. Kent (Adnet Systems, Inc. Greenbelt, MD, United States)
Farrell, William M. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
January 31, 2017
Publication Date
December 15, 2016
Publication Information
Publication: Geophysical Research Letters
Volume: 44
Issue: 1
ISSN: 0094-8276
Subject Category
Geophysics
Report/Patent Number
GSFC-E-DAA-TN38982
Funding Number(s)
CONTRACT_GRANT: NNG12PL17C
Distribution Limits
Public
Copyright
Other
Keywords
Stair-step
Flux
Spectra