Journal article
ARTEMIS Observations of Electron Cyclotron Harmonic Waves in the Lunar Plasma Environment
Geophysical research letters, Vol.52(15), e2025GL116971
08/16/2025
DOI: 10.1029/2025GL116971
Abstract
We report Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) observations of electron cyclotron harmonic (ECH) emissions in the lunar plasma environment. ECH emissions are correlated with electron loss‐cone distributions and electron beams during periods of magnetic connection to the lunar surface. Intermittent connection to lunar crustal magnetic anomalies correlates with a reduction or cessation in the ECH waves. In one case, ECH waves diminish in the presence of an additional cold (10 eV) electron population despite the presence of an electron beam and loss‐cone distribution. The spatial occurrence distributions show that ECH waves occur predominantly (97%) within the terrestrial magnetotail and within 1.5 lunar radii of the Moon‐Sun line. This is consistent with magnetic connection to the lunar surface and the formation of electron loss cones and/or electron beams while within the terrestrial magnetotail lobe. The full data set of ARTEMIS ECH observations represents a robust data set with which to test ECH wave formation theories.
Since Earth's Moon does not have a thick atmosphere or global magnetic field, ambient electrons from the Moon's space environment interact directly with the lunar surface. These electrons can be absorbed at the surface and liberate new electrons from the surface, known as secondary electrons. The absorption of electrons from the Moon's space environment and/or the production of secondary electrons may lead to conditions in which the electromagnetic fields are unstable. This instabilities causes different types of waves to appear in the electric and magnetic fields. We report observations of electrostatic waves known as “electron cyclotron harmonics” that are observed near the Moon by NASA's Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft and are correlated with the absorption of ambient electrons and the generation of secondary electrons. We show two example observations of these waves, highlighting key features and correlations. We also show a statistical analysis of where these waves occur in the lunar plasma environment by analyzing over 13 years of ARTEMIS observations. The electron cyclotron harmonics are most frequently seen when the Moon crosses the Earth's downstream magnetotail once per month. These waves also occur most frequently along the Moon‐Sun line, likely due to the way in which Earth's magnetic fields are oriented within the magnetotail.
Electron cyclotron harmonic (ECH) emissions are observed with the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft in the lunar plasma environment ECH emission is correlated with electron loss cones and electron beams resulting from magnetic connection to the lunar surface ECH at the Moon are highly concentrated within the terrestrial magnetotail and along the Moon‐Sun line
Details
- Title: Subtitle
- ARTEMIS Observations of Electron Cyclotron Harmonic Waves in the Lunar Plasma Environment
- Creators
- A. R. Poppe - University of California, BerkeleyJ. S. Halekas - University of IowaD. M. Malaspina - University of Colorado BoulderX. Zhang - University of California, Los AngelesV. Angelopoulos - University of California, Los Angeles
- Resource Type
- Journal article
- Publication Details
- Geophysical research letters, Vol.52(15), e2025GL116971
- DOI
- 10.1029/2025GL116971
- ISSN
- 0094-8276
- eISSN
- 1944-8007
- Publisher
- AMER GEOPHYSICAL UNION
- Grant note
- Heliophysics Division: NAS5-02099 NASA
The authors gratefully acknowledge support from the THEMIS-ARTEMIS mission, NASA Grant NAS5-02099, C. W. Carlson and J. P. McFadden for use of ESA data, and J. W. Bonnell for the use of EFI data and constructive comments to the manuscript.
- Language
- English
- Date published
- 08/16/2025
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984945083902771
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