ArticlePublisher preview available

Global Maps of Solar Wind Electron Modification by Electrostatic Waves Above the Lunar Day Side: Kaguya Observations

Geophysical Research Letters

September 2021
48(17)

DOI:10.1029/2021GL095260

Authors:

Yuki Harada

Kyoto University

Yoshiya Kasahara

Kanazawa University

Masaki N. Nishino

Japan Aerospace Exploration Agency

Show all 9 authorsHide

The Moon drives observable perturbations in the upstream solar wind in a similar manner to the terrestrial foreshock. Recent observations suggested that lunar dayside electrostatic waves can arise from two different driving mechanisms, both involving reflected particles from lunar crustal magnetic fields. However, their association with the global distribution of lunar magnetic anomalies have not been fully characterized. Here we exploit polar orbiting Kaguya to generate first global maps of electrostatic waves and solar wind electron modification above the day side of the Moon. The maps clearly demonstrate that the two signatures are correlated with lunar crustal magnetic fields. Additionally, we observe different characteristics of electron modification for different interplanetary magnetic field orientations. The lunar crustal magnetic fields cause a wide range of reflected electron and ion intensities, thereby serving as a test bed to investigate the relative roles of reflected particles on wave excitation and particle heating.

An example case of electrostatic waves and solar wind electron modification above the day side of the Moon observed by Kaguya. (Left) Time‐series data obtained by Kaguya and Wind at 05:30–06:20 UT on March 10, 2008: (a) pitch angle distributions of 164 eV electrons measured by Wind, time‐shifted to the Moon position; (b) downward ion energy spectra from the Ion Energy Analyzer (IEA) in units of differential energy flux (D.E.F., eV s−1cm−2sr−1eV−1); (c) upward ion energy spectra from the Ion Mass Analyzer (IMA); (d) downward electron energy spectra from the Electron Spectrum Analyzer (ESA)‐S2; (e) upward electron energy spectra from ESA‐S1; (f) pitch angle distributions of 150–250 eV electrons from ESA‐S1 and ‐S2; (g) perpendicular (60–90°) to parallel (0–30°) flux ratios of downward electrons (downward pitch angle ranges, 0–90° and 90–180°, are selected according to the magnetic field inclination) at Kaguya (black) and those from Wind in the corresponding pitch angle ranges (blue) derived from the pitch angle distributions shown in Figures 1f and 1a, respectively; (h) magnetic fields in SSE coordinates; (i) magnetic field connection estimated from straight field line extrapolation (black: no connection, red: +B connected to the Moon, green: −B connected to the Moon); and (j) electric field frequency spectra from the Lunar Radar Sounder (LRS) waveform capture (WFC)‐H receiver. The gaps in Figures 1b, 1d, and 1f are associated with the solar UV contamination to IEA and ESA‐S2. (Right) Kaguya orbital trajectories (magenta) in Selenocentric Solar Ecliptic (SSE), Geocentric Solar Ecliptic (GSE), and selenographic coordinates: (k) XSSE‐YSSE; (l) XGSE‐YGSE; (m) XSSE‐ZSSE; (n) YSSE‐ZSSE; and (o) selenographic longitude‐latitude with contours denoting 2 nT crustal field level at a 30 km altitude computed from the Tsunakawa et al. (2015) surface vector mapping (SVM) model.

…

Global maps of wave electric field and solar wind electron modification above the day side of the Moon. Electric field wave power at 1–3 kHz for (a) connected and (b) unconnected magnetic field lines, and for connected field lines with downward strahl electrons (c) present and (d) absent in the time‐shifted Wind data. Perpendicular to parallel flux ratios of downward 150–250 eV electrons at Kaguya when downward strahl electrons are present in the time‐shifted Wind data for (e) connected and (f) unconnected intervals. Figures 2b and 2f show the data as a function of longitude and latitude of the spacecraft position, while the other maps use the location of the field line foot point (FP) on the Moon. The magenta boxes denote the strong crustal field region analyzed in Figures 3b1–3c2.

…

(1) Two dimensional histograms as a function of perpendicular to parallel flux ratios of downward 150–250 eV electrons and 1–3 kHz electric field wave power measured by Kaguya in the presence of strahl electrons in the time‐shifted Wind data from (a) all data, and the strong crustal field region under (b) small (0–30°) and (c) large (60–90°) interplanetary magnetic field (IMF) cone angle conditions. The black line represents the mode in each electric field power bin. (2) Normalized histograms of perpendicular to parallel flux ratios of downward electrons. Different colors denote different ranges of the electric field wave power.

…

Schematic illustration of the observed properties and proposed processes regarding electrostatic waves and modification of incoming electrons above the lunar day side in the solar wind for (a) radial interplanetary magnetic field (IMF) (BIMF∥VSW) and (b) IMF perpendicular to the solar wind flow (BIMF⊥VSW) conditions. For each of the unmagnetized (a1 and b1), weakly magnetized (a2 and b2), and strong magnetized (a3 and b3) regions, the direction and topology of magnetic field lines, the presence or absence of electrostatic waves and associated instabilities (electron two stream instability, ETSI, and electron cyclotron drift instability, ECDI), and shapes of electron velocity distribution functions (VDFs) are illustrated.

…

Figures - available from: Geophysical Research Letters

This content is subject to copyright. Terms and conditions apply.

A preview of this full-text is provided by Wiley.

Learn more

Content available from Geophysical Research Letters

This content is subject to copyright. Terms and conditions apply.

1. Introduction

Despite the absence of a global magnetosphere of intrinsic or induced nature, the Moon drives many ob-

servable disturbances in the ambient plasma through absorption, scattering, reflection, and emission of

charged particles by the lunar surface and crustal magnetic fields (Halekas etal.,2011; Saito etal.,2010).

The Moon-plasma interaction generates numerous types of plasma waves observed as electric and magnetic

field fluctuations in a wide range of frequencies (Harada & Halekas,2016; Nakagawa,2016).

Among the rich variety of Moon-related plasma waves, upstream electrostatic waves are suggested to modi-

fy velocity distributions of incoming solar wind electrons, which otherwise have no way to sense the Moon's

existence beforehand in the collisionless, super-Alfvénic solar wind plasma. Intense broadband electrostatic

noise (BEN) above lunar magnetic anomalies located on the lunar day side was first observed by Kaguya

(Hashimoto etal.,2010). Hashimoto etal.(2010) showed from waveform analysis that BEN consists of elec-

trostatic solitary waves (ESWs) with predominantly parallel electric field (



) structures, and proposed that

these ESWs are generated by the electron two stream instabilities (ETSIs) (e.g., Omura etal.,1996,1999) be-

tween incident electrons and upward, magnetically reflected electron beams. Such beam- or conic-like dis-

tributions of upward electrons are commonly observed above lunar magnetic anomalies (Halekas, Poppe,

Delory, etal.,2012), partly resulting from energy gain by reflection from a moving obstacle (Halekas, Poppe,

Abstract The Moon drives observable perturbations in the upstream solar wind in a similar manner

to the terrestrial foreshock. Recent observations suggested that lunar dayside electrostatic waves can arise

from two different driving mechanisms, both involving reflected particles from lunar crustal magnetic

fields. However, their association with the global distribution of lunar magnetic anomalies have not been

fully characterized. Here we exploit polar orbiting Kaguya to generate first global maps of electrostatic

waves and solar wind electron modification above the day side of the Moon. The maps clearly demonstrate

that the two signatures are correlated with lunar crustal magnetic fields. Additionally, we observe different

characteristics of electron modification for different interplanetary magnetic field orientations. The lunar

crustal magnetic fields cause a wide range of reflected electron and ion intensities, thereby serving as a

test bed to investigate the relative roles of reflected particles on wave excitation and particle heating.

Plain Language Summary The Moon drives a variety of waves in the surrounding ionized

gas. In this study, we make a world map showing the population of one of these waves, electrostatic waves,

on the Moon. The wave map shows a clear pattern resembling the lunar magnetic field map. This suggests

that the waves are caused by reflection of charged particles from the localized magnetic field of the Moon.

Additionally, we observe a change in incoming electrons from the Sun when the waves are present.

Our results demonstrate that the space around the Moon is a useful place to study interactions between

particles and waves, which occur in many other places in space.

HARADA ET AL.

Global Maps of Solar Wind Electron Modification by

Electrostatic Waves Above the Lunar Day Side: Kaguya

Observations

Yuki Harada1 , Yoshiya Kasahara2 , Masaki N. Nishino3 , Satoshi Kurita4 ,

Yoshifumi Saito3 , Shoichiro Yokota5, Atsushi Kumamoto6 , Futoshi Takahashi7, and

Hisayoshi Shimizu8

1Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan, 2Information Media Center,

Kanazawa University, Kanazawa, Japan, 3Institute of Space and Astronautical Science, Japan Aerospace Exploration

Agency, Sagamihara, Japan, 4Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan,

5Graduate School of Science, Osaka University, Osaka, Japan, 6Graduate School of Science, Tohoku University, Sendai,

Japan, 7Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan, 8Earthquake Research

Institute, University of Tokyo, Tokyo, Japan

Key Points:

• We present first global maps of

electrostatic waves and solar wind

electron modification on the lunar

day side

• The wave generation and resulting

solar wind electron modification are

clearly controlled by lunar crustal

magnetic fields

• Two types of electron-wave

interactions are observed under

different interplanetary magnetic

field orientations

Correspondence to:

Y. Harada,

haraday@kugi.kyoto-u.ac.jp

Citation:

Harada, Y., Kasahara, Y., Nishino, M.

N., Kurita, S., Saito, Y., Yokota, S., etal.

(2021). Global maps of solar wind

electron modification by electrostatic

waves above the lunar day side: Kaguya

observations. Geophysical Research

Letters, 48, e2021GL095260. https://doi.

org/10.1029/2021GL095260

Received 14 JUL 2021

Accepted 17 AUG 2021

10.1029/2021GL095260

RESEARCH LETTER

1 of 9

Survey of Electron Heating and Implications for Wave‐Particle Interactions Near the Lunar Surface: ARTEMIS Observations

Article

Full-text available

Dec 2022

Interactions between the incident solar wind plasma and lunar crustal magnetic fields can lead to modifications in electron and ion dynamics that can result in the generation of electrostatic and electromagnetic waves. The resulting waves can then interact with the ambient electrons, leading to perpendicular and/or parallel electron heating. We analyze 10 years of data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun mission, when the spacecraft was within 200 km of the dayside lunar surface and within the solar wind, in order to characterize the near‐Moon plasma environment. We find that as the reflected ion density increases, electrostatic waves associated with plasma conditions favorable for the electron cyclotron drift instability play an increasingly important role in perpendicular electron heating, while electromagnetic interactions display the opposite trend. Additionally, we find that electrostatic waves associated with parallel heating exhibit plasma characteristics that are consistent with both the electron two‐stream instability and the modified two‐stream instability.

Lunar Resource Exploitation and Anticipated Risks During The Development of The Moon: Considering Selenological Aspects月の資源開発と開発時のリスク：月質学的観点から

Article

Jun 2024

In this paper, we provide an overview of the lunar rocks and selenology (geology of the Moon), and also summarize an up-to-date concept of lunar resources and their exploitation. Furthermore, the environmental and disaster risks during the development of the Moon contrast with them on Earth, by taking selenological aspects into consideration. Many plans for lunar exploration and landing on the lunar surface are in progress, and one of the next-step activities on the Moon is constructing living and resource-developing facilities. The specific forms and requirements for these constructions will become clear as the plans progress realistically. It is essential for further discussions to estimate the varieties, characteristics, and quantities of materials that can be sourced from the Moon. Additionally, unique responses are required for lunar development, because the lunar environment differs from the terrestrial one. It is necessary to keep abreast of new knowledge to ensure safe and effective lunar development, since many new findings about the selenology and environment of the Moon, which in some cases are modifying established theories and hypotheses, are acquired every moment.

Electrostatic Waves and Electron Heating Observed Over Lunar Crustal Magnetic Anomalies

Article

Full-text available

Apr 2021

Above lunar crustal magnetic anomalies, large fractions of solar wind electrons and ions can be scattered and stream back toward the solar wind flow, leading to a number of interesting effects such as electrostatic instabilities and waves. These electrostatic structures can also interact with the background plasma, resulting in electron heating and scattering. We study the electrostatic waves and electron heating observed over the lunar magnetic anomalies by analyzing data from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. Based on the analysis of two lunar flybys in 2011 and 2013, we find that the electron two‐stream instability (ETSI) and electron cyclotron drift instability (ECDI) may play an important role in driving the electrostatic waves. We also find that ECDI, along with the modified two‐stream instability (MTSI), may provide the mechanisms responsible for substantial isotropic electron heating over the lunar magnetic anomalies.

Diffusive scattering of electrons by electron holes around injection fronts

Article

Full-text available

Feb 2017

Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi-linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test-particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce-averaged diffusion coefficients and demonstrate their dependence on the EH spatial distribution (latitudinal extent and spatial filling factor) and individual EH parameters (amplitude of electrostatic potential, velocity, spatial scales). We show that EHs can drive pitch-angle scattering of 5 keV electrons at rates 10 −2 − 10 −4 s −1 and, hence, can contribute to electron losses and conjugated diffuse aurora brightenings. The momentum and pitch-angle scattering rates can be comparable, so that EHs can also provide efficient electron heating. The scattering rates driven by EHs at L−shells L ∼ 5 − 8 are comparable to those due to chorus waves and may exceed those due to electron cyclotron harmonics.

ULF/ELF Waves in Near-Moon Space: Keiling/Low-Frequency Waves in Space Plasmas

Chapter

Full-text available

Feb 2016

Tomoko Nakagawa

The reflection of the solar wind protons is equivalent to a beam injection against the solar wind flow. It is expected to produce a ring beam with a 3D distribution function in many cases. The reflected protons are responsible for the generation of ultra-low-frequency (ULF) waves at ˜0.01 Hz and narrowband waves at ˜1 Hz in the extremely low frequency (ELF) range through resonant interaction with magnetohydrodynamic waves and whistler mode waves in the solar wind, respectively. This chapter discusses these commonly observed waves in the near-Moon space. The sinusoidal waveforms and sharp spectra of the monochromatic ELF waves are impressive, but commonly observed are non-monochromatic waves in the ELF range ˜0.03-10 Hz. Some of the solar wind protons reflected by the dayside lunar surface or crustal magnetic field gyrate around the solar wind magnetic field and can access the center of the wake owing to the large Larmour radius.

Lunar precursor effects in the solar wind and terrestrial magnetosphere

Article

Full-text available

May 2012

The two ARTEMIS probes observe significant precursor activity upstream from the Moon, when magnetically connected to the dayside lunar surface. The most common signature consists of high levels of whistler wave activity near half of the electron cyclotron frequency. This precursor activity extends to distances of many thousands of km, in both the solar wind and terrestrial magnetosphere. In the magnetosphere, electrons reflect from a combination of magnetic and electrostatic fields above the lunar surface, forming loss cone distributions. In the solar wind they generally form conics, as a result of reflection from an obstacle moving with respect to the plasma frame (just as at a shock). The anisotropy associated with these reflected electrons provides the free energy source for the whistlers, with cyclotron resonance conditions met between the reflected source population and Moonward-propagating waves. These waves can in turn affect incoming plasma, and we observe significant perpendicular electron heating and plasma density depletions in some cases. In the magnetosphere, we also observe broadband electrostatic modes driven by beams of secondary electrons and/or photoelectrons accelerated outward from the surface. We also occasionally see waves near the ion cyclotron frequency in the magnetosphere. These lower frequency waves, which may result from the presence of ions of lunar origin, modulate the whistlers described above, as well as the electrons. Taken together, our observations suggest that the presence of the Moon leads to the formation of an upstream region analogous in many ways to the terrestrial electron foreshock.

ARTEMIS observations of the solar wind proton scattering function from lunar crustal magnetic anomalies: REFLECTED LUNAR PROTONS

Article

Apr 2017

Despite their small scales, lunar crustal magnetic fields are routinely associated with observations of reflected and/or back-streaming populations of solar wind protons. Solar wind proton reflection locally reduces the rate of space weathering of the lunar regolith, depresses local sputtering rates of neutrals into the lunar exosphere, and can trigger electromagnetic waves and small-scale collisionless shocks in the near-lunar space plasma environment. Thus, knowledge of both the magnitude and scattering function of solar wind protons from magnetic anomalies is crucial in understanding a wide variety of planetary phenomena at the Moon. We have compiled 5.5 years of ARTEMIS observations of reflected protons at the Moon and used a Liouville tracing method to ascertain each proton's reflection location and scattering angles. We find that solar wind proton reflection is largely correlated with crustal magnetic field strength, with anomalies such as South Pole/Aitken Basin (SPA), Mare Marginis, and Gerasimovich reflecting on average 5-12% of the solar wind flux while the un-magnetized surface reflects between 0.1-1% in charged form. We present the scattering function of solar wind protons off of the SPA anomaly, showing that the scattering transitions from isotropic at low solar zenith angles to strongly forward-scattering at solar zenith angles near 90° . Such scattering is consistent with simulations that have suggested electrostatic fields as the primary mechanism for solar wind proton reflection from crustal magnetic anomalies.

Upstream Waves and Particles at the Moon

Chapter

Feb 2016

This chapter presents an up-to-date catalog of Moon-related particle populations and lunar upstream waves obtained from in-situ measurements at low (<~100 km) and high altitudes, aimed at organizing and clarifying the currently available information on this complex region, where multiple categories of waves and particles coexist. It then briefly outlines the observed properties of a variety of classes of lunar upstream waves, as well as their generation mechanisms currently proposed, in association with the lunar upstream particle distributions. The lunar upstream region magnetically connected to the Moon and its wake, the fore-moon, represents a remarkably rich zoo of different classes of waves and different types of particles. Although recent observations have substantially enhanced our knowledge by revealing a number of new categories of upstream particles and waves at the Moon, many fundamental questions remain unanswered, and these are outlined in the chapter.

Statistical characterization of the foremoon particle and wave morphology: ARTEMIS observations

Article

Jun 2015

Although the zeroth-order picture of the Moon-solar wind interaction involves no upstream perturbation, the presence of the Moon does affect the upstream plasma in a variety of ways. In this paper, a large volume of data obtained by the dual-probe Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission are used to characterize the large-scale morphology of the “foremoon,” which is defined as the region upstream of the Moon and its wake that contains Moon-related particles and waves. Solar wind ions reflected from the unshielded surface and by crustal magnetic fields, together with heavy ions of lunar surface/exospheric origin, are picked up by the solar wind magnetic and electric fields. Partially coinciding with populations of these Moon-related ions, ∼0.01 Hz and ∼1 Hz magnetic field fluctuations are observed. The morphology of the Moon-related ion and wave distributions is well organized by the upstream magnetic field direction. In addition, the low-frequency wave distributions depend on the upstream Alfvén Mach numbers, suggesting that propagation effects also play a role in determining the wave foremoon morphology. Occurrence of modified electron velocity distributions and higher-frequency, electromagnetic, and electrostatic waves is primarily controlled by magnetic connection to the Moon and its wake. These statistical results observationally demonstrate the large-scale properties of the foremoon and upstream-parameter control thereof.

Surface vector mapping of magnetic anomalies over the Moon using Kaguya and Lunar Prospector observations: SVM of magnetic anomalies over the Moon

Article

May 2015

We have provided preliminary global maps of three components of the lunar magnetic anomaly on the surface applying the surface vector mapping (SVM) method. The data used in the present study consist of about 5 million observations of the lunar magnetic field at 10–45 km altitudes by Kaguya and Lunar Prospector. The lunar magnetic anomalies were mapped at 0.2° equi-distance points on the surface by the SVM method, showing the highest intensity of 718 nT in the Crisium antipodal region. Overall features on the SVM maps indicate that elongating magnetic anomalies are likely to be dominant on the Moon except for the young large basins with the impact demagnetization. Remarkable demagnetization features suggested by previous studies are also recognized at Hertzsprung and Kolorev craters on the farside. These features indicate that demagnetized areas extend to about 1–2 radii of the basins/craters. There are well-isolated central magnetic anomalies at four craters: Leibnitz, Aitken, Jules Verne, and Grimaldi craters. Their magnetic poles through the dipole source approximation suggest occurrence of the polar wander prior to 3.3–3.5 Ga. When compared with high-albedo markings at several magnetic anomalies such as the Reiner Gamma anomalies, three-dimensional structures of the magnetic field on/near the surface are well correlated with high-albedo areas. These results indicate that the global SVM maps are useful for the study of the lunar magnetic anomalies in comparison with various geological and geophysical data.

Extended lunar precursor regions: Electron-wave interaction

Article

Nov 2014

We present ARTEMIS observations of electron-wave interactions which extend to quite large distances upstream from the Moon. We first study electron velocity distributions and wave spectra on an event basis. In both the solar wind and terrestrial plasma sheet, we observe strong whistler wave activity on the magnetic field lines connected to the dayside lunar surface. These whistlers are most likely driven by the anisotropy of upward electrons caused by surface absorption. The whistler growth rates computed from the measured electron distributions successfully reproduced the spectral characteristics of the observed ~100 Hz narrowband oscillations and those reaching lower frequencies. Meanwhile, the incoming solar wind strahl beam is occasionally isotropized near the Moon and broadband electrostatic waves are observed simultaneously, suggesting streaming instabilities between the incoming and outgoing beams. Based on the case study, we statistically survey the spatial variations of the characteristic quantities of the upstream electron-wave interactions. Both the electron anisotropy and electromagnetic wave intensity decay with increasing field-line distances but remain higher than the ambient level at 6 lunar radii (~10,000 km) or more. The strahl electron isotropization and electrostatic waves are found mainly at lower altitudes below one lunar radius. The electron anisotropy and whistler intensity exhibit clear anti-correlation with crustal magnetic fields, indicating that the magnetic anomalies suppress the whistler wave growth. The ARTEMIS observations convincingly illustrate that the lunar influence on electrons reaches out to 6 lunar radii or more upstream from the Moon.

Solar wind spatial scales in and comparison of hourly Wind and ACE plasma and magnetic field data

Article

Feb 2005

Hourly averaged interplanetary magnetic field (IMF) and plasma data from the Advanced Composition Explorer (ACE) and Wind spacecraft, generated from 1 to 4 min resolution data time-shifted to Earth have been analyzed for systematic and random differences. ACE moments-based proton densities are larger than Wind/Solar Wind Experiment (SWE) fits-based densities by up to 18%, depending on solar wind speed. ACE temperatures are less than Wind/SWE temperatures by up to ∼25%. ACE densities and temperatures were normalized to equivalent Wind values in National Space Science Data Center's creation of the OMNI 2 data set that contains 1963–2004 solar wind field and plasma data and other data. For times of ACE-Wind transverse separations

Global Maps of Solar Wind Electron Modification by Electrostatic Waves Above the Lunar Day Side: Kaguya Observations

Abstract and Figures

Recommended publications

The effects of reflected protons on the plasma environment of the Moon for parallel interplanetary m...

An event study on broadband electric field noises and electron distributions in the lunar wake bound...

Decrease of the interplanetary magnetic field strength on the lunar dayside and over the polar regio...

Control of lunar external magnetic enhancements by IMF polarity: A case study

Smallest Scale Magnetic Field Compressions Generated by the Solar Wind Interaction with the Moon