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

Han-Wen Shen; Jasper Halekas; Andrew R Poppe

doi:10.3847/1538-4357/ad40a4

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

Journal article

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

Han-Wen Shen, Jasper Halekas and Andrew R Poppe

The Astrophysical journal, Vol.967(2), 84

06/01/2024

DOI: 10.3847/1538-4357/ad40a4

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Abstract

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.

Altitude

Electrodynamics

Electromagnetic fields

Exosphere

Fluctuations

Ion flux

Ion fluxes

Ion trajectories

Ions

Magnetic anomalies

Magnetic fields

Magnetic flux

Moon

Neutral atoms

Spacecraft

Sputtering

Statistical analysis

Trajectory analysis

Details

Title: Subtitle: Dependence of Lunar Pickup Ion Flux on Source Location: ARTEMIS Observations
Creators: Han-Wen Shen - University of Iowa
Jasper Halekas - University of Iowa
Andrew R Poppe - University of California, Berkeley
Resource Type: Journal article
Publication Details: The Astrophysical journal, Vol.967(2), 84
Publisher: IOP Publishing
DOI: 10.3847/1538-4357/ad40a4
ISSN: 0004-637X
eISSN: 1538-4357
Language: English
Date published: 06/01/2024
Academic Unit: Physics and Astronomy
Record Identifier: 9984628216502771

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