Dependence of Lunar Pickup Ion Flux on Source Location: ARTEMIS Observations

The Moon is enveloped in an exosphere, which is comprised of a variety of neutral atoms and molecules. Once exospheric neutrals are ionized by photons, protons, or electrons from the Sun, the resulting ions are accelerated by the electromagnetic fields of their surroundings and can thereby travel aw...

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Bibliographic Details
Published in:The Astrophysical journal 2024-06, Vol.967 (2), p.84
Main Authors: Shen, Han-Wen, Halekas, Jasper S., Poppe, Andrew R.
Format: Article
Language:English
Subjects:
Altitude
Electrodynamics
Electromagnetic fields
Exosphere
Fluctuations
Ion flux
Ion fluxes
Ion trajectories
Ions
Lunar science
Magnetic anomalies
Magnetic fields
Magnetic flux
Moon
Neutral atoms
Solar wind
Space plasmas
Spacecraft
Sputtering
Statistical analysis
The Moon
Trajectory analysis
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Summary:The Moon is enveloped in an exosphere, which is comprised of a variety of neutral atoms and molecules. Once exospheric neutrals are ionized by photons, protons, or electrons from the Sun, the resulting ions are accelerated by the electromagnetic fields of their surroundings and can thereby travel away from their source locations. These ions are the so-called pickup ions and are frequently observed by the two Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) spacecraft. In this study, we identify 115 events from an 11 yr period of ARTEMIS observations, which contain a total of 11,987 samples for our statistics. By using analytical ion trajectory calculations, we trace the source location of each pickup ion observation. Most pickup ion trajectories originate near the subsolar point, consistent with the efficiency of sputtering. We find that the flux of pickup ions strongly anticorrelates with the source altitude, providing indirect evidence of decreasing exospheric ion flux with increasing altitude. We also find that the flux of pickup ions does not show a significant relationship with the crustal magnetic field intensity. This implies that a depression of sputtering efficiency or the trapping of near-surface freshly born ions by a crustal magnetic anomaly may not reduce the subsequent pickup ion flux as effectively as expected. In summary, the present paper provides a statistical view of lunar pickup ion fluxes in association with the altitude, local time, and local crustal magnetic field of their source locations.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ad40a4