A Statistical Study of the Moon's Magnetotail Plasma Environment

Abstract

This study investigates the lunar plasma environment when embedded within Earth's magnetotail. We use data from 10 years of tail crossings by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in orbit around the Moon. We separate the plasma environments by magnetosheath‐like, magnetotail lobe‐like, and plasma sheet‐like conditions. Our findings highlight that the lobe‐like plasma is associated with low densities and a strong magnetic field, while the plasma sheet is characterized by higher densities and a weaker magnetic field. These regions are flanked by the fast, predominantly tailward flows of the terrestrial magnetosheath. During a single lunar crossing, however, the magnetotail displays a wide range of variability, with transient features—including reconnection events—intermixed between periods of lobe‐like or sheet‐like conditions. We compare and contrast the Moon's local magnetotail plasma to the environments near various outer‐planet moons. In doing so, we find that properties of the ambient lunar plasma are, at times, unique to the terrestrial magnetotail, while at others, may resemble those near the Jovian, Saturnian, and Neptunian moons. These findings highlight the complementary role of the ARTEMIS mission in providing a deeper understanding of the plasma interactions of the outer‐planet moons.

Thin Current Sheets in the Magnetotail at Lunar Distances: Statistics of ARTEMIS Observations

“…Therefore, our results confirm the idea of Liuzzo et al. (2022), that the middle magnetotail is a natural plasma laboratory for in situ CS investigations across a wide range of plasma characteristics. Moreover, observations of such partially force‐free CSs provide a unique opportunity for the verification of models describing equilibrium for CSs without a normal magnetic field component, B n = 0, (e.g., Allanson et al., 2015; Neukirch, Vasko, et al., 2020, and references therein) and with a finite B n ≠ 0 (e.g., An et al., 2023; Artemyev, 2011; Mingalev et al., 2012; Vasko et al., 2014).…”

“…We can use it to estimate the CS's spatial scale (thicknesses) and current density. ARTEMIS started operating in 2011 and its measurements now encompass 12 years of observations (see large statistics of plasma and magnetic field characteristics in Liuzzo et al., 2022; Runov et al., 2023). In this study, we use data collected between 2012 and 2022, covering 11 years in total (one full solar cycle).…”

On the Role of Kinetic Alfven Waves in the Magnetosheath Ion Thermalization Around the Night‐Side Magnetopause

“…Ion temperature components, which are set as $${T}_{{\Vert }_{0}}={T}_{{\perp }_{0}}=300$$ eV initially, grow to $${\sim} 3\times {T}_{{\Vert }_{0}}\sim 1$$ keV and $$4\times {T}_{{\perp }_{0}}\sim 1.2$$ keV close to the magnetopause ( x / L ∼ −3) within the simulation time. Therefore, a transition layer forms in between the magnetosheath and the magnetosphere, where the ion temperature is as great as typical magnetospheric ion temperature at the lunar distance (see statistics by Artemyev, Angelopoulos, Hietala, et al., 2017; Liuzzo et al., 2022).…”

Properties of Quiet Magnetotail Plasma Sheet at Lunar Distances

“…Recently, Liuzzo et al. (2022) performed a large statistical study of magnetic field and plasma parameters observed by ARTEMIS in the nightside magnetosphere, selecting intervals of the probe's location within 20° in longitude of the local midnight meridian (i.e., the GSE X ‐axis). They distinguish “magnetosheath‐like,” “magnetotail lobe‐like,” and “plasma sheet‐like” plasma environments using criteria which include magnetic field direction and magnitude and plasma density.…”

“…No selection was made according to geomagnetic activity or local plasma flow conditions. The study by Liuzzo et al (2022) has revealed broad dynamic ranges of field and plasma parameters variations. Certain characteristics, including high density (up to 10 cm −3 ) in "magnetotail lobe-like" and "plasma sheet-like" environments, |B x | < 5 nT and |B z | ≈ 10 nT in the "lobe-like" environment, and the prevalence of earthward fast flows in the "plasma sheet-like" environment, require further investigation.…”