The Effects of ICME Composition on the Sputtered Component of the Lunar Exosphere
Abstract
Charged-particle sputtering is a fundamental process that contributes to the generation of the Moon's neutral exosphere. Neutral sputtering rates are dependent on the speed, flux, and composition of the incident charged-particle populations, all of which are variable at the Moon's orbit. Dramatic increases in the neutral sputtering rate are likely driven by the impact of interplanetary coronal mass ejections (ICMEs). ICMEs have enhanced densities and speeds, as well as changes in their underlying composition with respect to typical solar wind values. Here, we study the role that ion composition has on the overall contributions to neutral sputtering at the Moon by analyzing in situ observations by NASA's Advanced Composition Explorer (ACE) mission. A pre-existing catalog of ICMEs at 1 au is used to extract relevant time periods and convolve compositionally resolved ion fluxes with laboratory sputtering yields. Median sputtered fluxes increase by factors of 2.4× and 1.5× the average solar wind value during ICME sheath and ejecta periods, respectively. Protons typically dominate sputtered fluxes from the Moon for all data, including during ICME sheath and ejecta periods; however, the contributions from alphas increases during ICME ejecta due to enhanced alpha-toproton ratios. Heavy ions, including C, O, Ne, Mg, Si, and Fe typically contribute less than 10% of the total sputtered flux. Furthermore, the relative contribution of heavy ions decreases during ICME ejecta driven by strong increases in the sputtered contribution from alphas. Overall, solar wind heavy ions play an important, although not dominant, role in sputtering of the Moon's surface.Plain Language Summary While the Moon does not have a thick atmosphere, it does possess a very thin atmosphere called an exosphere, formed in part when charged particles (ions) from interplanetary space impact the surface and eject individual atoms. This process is known as "sputttering" and is dependent on the flux and composition of ions that strike the surface. While sputtering rates at the Moon are reasonably understood under typical conditions, the Sun occasionally ejects large and fast amounts of material, known as interplanetary coronal mass ejections (ICMEs). ICMEs have different mixtures of ion compositions than typical; however, we do not fully understand how these changes affect lunar sputtering. We use 13 years of observations by NASA's Advanced Composition Explorer to quantify the changes to ion composition and sputtering rates at the Moon during ICMEs. We find that the overall rate of sputtering increases 1.5-2.4 times that of normal during ICMEs and that protons dominate the sputtering rates. We also see that during one portion of ICMEs, known as the ejecta, doubly charged helium ions (known as alphas) have increased contributions to sputtering. Heavy ions, including carbon, oxygen, and iron, only contribute between 5% and 10% of the total sputtering, even during ICMEs.
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BibTeX
@article{poppe2026effects,
title = {{The Effects of ICME Composition on the Sputtered Component of the Lunar Exosphere}},
author = {Andrew R Poppe and Quentin Nénon and Paul S Szabo and Shane C Mogan and Christina O Lee},
journal = {Journal of Geophysical Research. Planets},
year = {2026},
month = oct,
doi = {10.1029/2026je009972},
url = {https://hal.science/hal-05800923v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - The Effects of ICME Composition on the Sputtered Component of the Lunar Exosphere
AU - Andrew R Poppe
AU - Quentin Nénon
AU - Paul S Szabo
AU - Shane C Mogan
AU - Christina O Lee
PY - 2026
DA - 2026/10/12
JO - Journal of Geophysical Research. Planets
DO - 10.1029/2026je009972
UR - https://hal.science/hal-05800923v1
AB - Charged-particle sputtering is a fundamental process that contributes to the generation of the Moon's neutral exosphere. Neutral sputtering rates are dependent on the speed, flux, and composition of the incident charged-particle populations, all of which are variable at the Moon's orbit. Dramatic increases in the neutral sputtering rate are likely driven by the impact of interplanetary coronal mass ejections (ICMEs). ICMEs have enhanced densities and speeds, as well as changes in their underlying composition with respect to typical solar wind values. Here, we study the role that ion composition has on the overall contributions to neutral sputtering at the Moon by analyzing in situ observations by NASA's Advanced Composition Explorer (ACE) mission. A pre-existing catalog of ICMEs at 1 au is used to extract relevant time periods and convolve compositionally resolved ion fluxes with laboratory sputtering yields. Median sputtered fluxes increase by factors of 2.4× and 1.5× the average solar wind value during ICME sheath and ejecta periods, respectively. Protons typically dominate sputtered fluxes from the Moon for all data, including during ICME sheath and ejecta periods; however, the contributions from alphas increases during ICME ejecta due to enhanced alpha-toproton ratios. Heavy ions, including C, O, Ne, Mg, Si, and Fe typically contribute less than 10% of the total sputtered flux. Furthermore, the relative contribution of heavy ions decreases during ICME ejecta driven by strong increases in the sputtered contribution from alphas. Overall, solar wind heavy ions play an important, although not dominant, role in sputtering of the Moon's surface.Plain Language Summary While the Moon does not have a thick atmosphere, it does possess a very thin atmosphere called an exosphere, formed in part when charged particles (ions) from interplanetary space impact the surface and eject individual atoms. This process is known as "sputttering" and is dependent on the flux and composition of ions that strike the surface. While sputtering rates at the Moon are reasonably understood under typical conditions, the Sun occasionally ejects large and fast amounts of material, known as interplanetary coronal mass ejections (ICMEs). ICMEs have different mixtures of ion compositions than typical; however, we do not fully understand how these changes affect lunar sputtering. We use 13 years of observations by NASA's Advanced Composition Explorer to quantify the changes to ion composition and sputtering rates at the Moon during ICMEs. We find that the overall rate of sputtering increases 1.5-2.4 times that of normal during ICMEs and that protons dominate the sputtering rates. We also see that during one portion of ICMEs, known as the ejecta, doubly charged helium ions (known as alphas) have increased contributions to sputtering. Heavy ions, including carbon, oxygen, and iron, only contribute between 5% and 10% of the total sputtering, even during ICMEs.
SN - 2169-9097
SN - 2169-9100
ER -