Unrestricted Solar Energetic Particle Access to the Moon While Within the Terrestrial Magnetotail

Liuzzo, Lucas; Poppe, A. R.; Lee, Christina O.; Xu, Shaosui; Angelopoulos, Vassilis

doi:10.1029/2023gl103990

Cited by 2 publications

(1 citation statement)

References 57 publications

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“…First, the Moon only spends approximately one quarter of its orbit in the magnetotail, which plainly cannot account for the factor of 25 difference discussed above. Furthermore, recent analysis of in situ particle measurements at the Moon have shown that SEPs likely have broad access to the lunar environment even within the terrestrial magnetotail due to the "open" nature of magnetotail lobe field lines to the solar wind (Liuzzo et al 2023). Finally, shielding of specific locations on the lunar surface by the solid obstacle of the Moon itself, while highly effective at keV energies (e.g., Fatemi et al 2012), appears to yield only small or even negligible results at MeV energies (e.g., Xu et al 2017).…”

Section: Sep Shielding At the Moonmentioning

confidence: 99%

Solar Energetic Particle Track-production Rates at 1 au: Comparing In Situ Particle Fluxes with Lunar Sample-derived Track Densities

Poppe,

Szabo,

Imata

et al. 2023

ApJL

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Heavy (Z > 26) solar energetic particles (SEPs) with energies ∼1 MeV nucleon−1 are known to leave visible damage tracks in meteoritic materials. The density of such “solar flare tracks” in lunar and asteroidal samples has been used as a measure of a sample’s exposure time to space, yielding critical information on planetary space weathering rates, the dynamics and lifetimes of interplanetary dust grains, and the long-term history of solar particle fluxes. Knowledge of the SEP track accumulation rate in planetary materials at 1 au is critical for properly interpreting observed track densities. Here, we use in situ particle observations of the 0.50−3.0 MeV nuc−1 Fe-group SEP flux taken by NASA’s Advanced Composition Explorer (ACE) to calculate a flux of track-inducing particles at 1 au of 6.0 × 105 cm−2 yr−1 str−1. Using the observed energy spectrum of Fe-group SEPs, we find that the depth distribution of SEP-induced damage tracks inferred from ACE measurements matches closely to that recently measured in lunar sample 64455; however, the magnitude of the ACE-inferred rate is approximately 25× higher than that observed in the lunar sample. We discuss several hypotheses for the nature of this discrepancy, including inefficiencies in track formation, thermal annealing of lunar samples, erosion via space weathering processing, and variations in the SEP flux at the Moon, yet find no satisfactory explanation. We encourage further research on both the nature of SEP track formation in meteoritic materials and the flux of Fe-group SEPs at the lunar surface in recent and geologic times to resolve this discrepancy.

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Section: Sep Shielding At the Moonmentioning

confidence: 99%

Solar Energetic Particle Track-production Rates at 1 au: Comparing In Situ Particle Fluxes with Lunar Sample-derived Track Densities

Poppe,

Szabo,

Imata

et al. 2023

ApJL

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Solar Energetic Electron Access to the Moon Within the Terrestrial Magnetotail and Shadowing by the Lunar Surface

Liuzzo,

Poppe,

Lee

et al. 2024

Geophysical Research Letters

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We present measurements of 30–700 keV Solar Energetic Electrons (SEEs) near the Moon when within the terrestrial magnetotail by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft. Despite their detection deep within the tail, the incident flux and spectral shape of these electrons are nearly identical to measurements taken upstream of Earth in the solar wind by the Wind spacecraft; however, their pitch angle distribution is isotropized compared to the more field‐aligned distribution upstream. We illustrate that SEEs initially traveling Earthward precipitate onto the lunar far‐side, generating extended shadows in the cis‐lunar electron distribution. By modeling the dynamics of these electrons, we show that their precipitation patterns on the lunar near‐side are comparatively reduced. The non‐uniform precipitation and accessibility of potentially hazardous electrons to the Moon's surface are highly relevant in the context of astronaut safety during the planned exploration of the lunar environment.

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Unrestricted Solar Energetic Particle Access to the Moon While Within the Terrestrial Magnetotail

Cited by 2 publications

References 57 publications

Solar Energetic Particle Track-production Rates at 1 au: Comparing In Situ Particle Fluxes with Lunar Sample-derived Track Densities

Solar Energetic Particle Track-production Rates at 1 au: Comparing In Situ Particle Fluxes with Lunar Sample-derived Track Densities

Solar Energetic Electron Access to the Moon Within the Terrestrial Magnetotail and Shadowing by the Lunar Surface

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