Lunar Magnetic Anomalies Research Articles

Submicroscopic magnetite may be ubiquitous in the lunar regolith of the high-Ti region

Magnetite is rare on the Moon. The ubiquitous presence of magnetite in lunar soil has been hypothesized in previous Apollo Mössbauer spectroscopy and electron spin resonance studies, but there is currently no mineralogical evidence to prove it. Here, we report a large number of submicroscopic magnetite particles embedded within iron-sulfide on the surface of Chang’e-5 glass, with a close positive correlation between magnetite content and the TiO 2 content of the surrounding glass. The morphology and mineralogy of the iron-sulfide grains suggest that these magnetite particles formed via an impact process between iron-sulfide droplets and silicate glass melt, and ilmenite is necessary for magnetite formation. Magnetite in lunar glass is a potential candidate for the “magnetite-like” phase detected in the Apollo era and suggests that impact-induced submicroscopic magnetite may be ubiquitous in high-Ti regions of the Moon. Moreover, these impact-induced magnetite particles may be crucial for understanding the lunar magnetic anomalies and mineral components of the deep Moon.

Possibility of Lunar Crustal Magmatism Producing Strong Crustal Magnetism

AbstractThe Moon generated a long‐lived core dynamo magnetic field, with intensities at least episodically reaching ∼10–100 μT during the period prior to ∼3.56 Ga. While magnetic anomalies observed within impact basins are likely attributable to the presence of impactor‐added metal, other anomalies such as those associated with lunar swirls are not as conclusively linked to exogenic materials. This has led to the hypothesis that some anomalies may be related to magmatic features such as dikes, sills, and laccoliths. However, basalts returned from the Apollo missions are magnetized too weakly to produce the required magnetization intensities (>0.5 A/m). Here, we test the hypothesis that subsolidus reduction of ilmenite within or adjacent to slowly cooled mafic intrusive bodies could locally enhance metallic FeNi contents within the lunar crust. We find that reduction within hypabyssal dikes with high‐Ti or low‐Ti mare basalt compositions can produce sufficient FeNi grains to carry the minimum >0.5 A/m magnetization intensity inferred for swirls, especially if ambient fields are >10 μT or if fine‐grained Fe‐Ni metals in the pseudo‐single domain grain size range are formed. Therefore, there exists a possibility that certain magnetic anomalies exhibiting various shapes such as linear, swarms, and elliptical patterns may be magmatic in origin. Our study highlights that the domain state of the magnetic carriers is an under‐appreciated factor in controlling a rock's magnetization intensity. The results of this study will help guide interpretations of lunar crustal field data acquired by future rovers that will traverse lunar magnetic anomalies.

Constraints on the Spatial Distribution of Lunar Crustal Magnetic Sources From Orbital Magnetic Field Data

AbstractSpacecraft measurements show that the crust of the Moon is heterogeneously magnetized. The sources of these magnetic anomalies are yet not fully understood, with most not being related to known geological structures or processes. Here, we use an inversion methodology that relies on the assumption of unidirectional magnetization, commonly referred to as Parker's method, to elucidate the origin of the magnetic sources by constraining the location and geometry of the underlying magnetization. This method has been used previously to infer the direction of the underlying magnetization but it has not been tested as to whether it can infer the geometry of the source. The performance of the method is here assessed by conducting a variety of tests, using synthetic magnetized bodies of different geometries mimicking the main geological structures potentially magnetized within the lunar crust. Results from our tests show that this method successfully localizes and delineates the two‐dimensional surface projection of subsurface three‐dimensional magnetized bodies, provided their magnetization is close to unidirectional and the magnetic field data are of sufficient spatial resolution and reasonable signal‐to‐noise ratio. We applied this inversion method to two different lunar magnetic anomalies, the Mendel‐Rydberg impact basin and the Reiner Gamma swirl. For Mendel‐Rydberg, our analysis shows that the strongest magnetic sources are located within the basin's inner ring, whereas for Reiner Gamma, the strongest magnetic sources form a narrow dike‐like body that emanates from the center of the Marius Hills volcanic complex.

Properties of Lunar Dust and Their Migration on the Moon

Lunar dust, the finest fraction of lunar regolith, has undergone important space weathering on the Moon. It not only serves as a record of the evolution of the lunar surface environment and the modification of mineral properties, but also influences the lunar surface environment through dust transport. Our current understanding of the properties and transport mechanisms of lunar dust on the lunar surface, however, remains limited. With rapid development of lunar exploration, it is necessary to further study the problem and meet the need of future lunar exploration missions. The lunar surface is the primary environmental space where uncrewed lunar rover activity, crewed lunar exploration, and lunar base construction take place. The lunar dust will distribute in such a space area due to electrostatic lifting and impacted sputtering, which will pose a threat to lunar surface exploration activities. In addition, lunar dust transport is closely related to lunar horizon glow, lunar swirl, and lunar magnetic anomaly. Understanding the properties and transport mechanisms of lunar dust is key to comprehending the formation of these scientific phenomena. Therefore, a systematic and in-depth investigation of lunar dust properties and dust transport patterns is urgently required to advance lunar science and implement lunar exploration projects. In this study, we summarize the physical and chemical properties of lunar dust and our understanding of dust transport on the lunar surface, identify remaining challenges and issues in the study of lunar dust, and offer perspectives on this research field.

Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

Magnetized magma intrusions being sources of a weak and a strong lunar magnetic anomaly revealed by 3D distribution of magnetization

Global Hall MHD Simulations of the Solar Wind Implantation Flux on the Lunar Surface

The solar wind can directly interact with the lunar surface and provide an important source for surface space weathering and water generation. Here we study the solar wind implantation flux on the lunar surface with global Hall MHD simulations. The shielding effects of both the Earth’s magnetosphere and lunar magnetic anomalies are considered. It is found that a large-scale lunar mini-magnetosphere can be caused by the solar wind interaction with the magnetic anomalies on the lunar far side, which causes a large shielding area on the surface. In addition, the Earth’s magnetosphere brings a longitudinal variation in the implantation flux, with minimum fluxes at 0° longitude. With the integrated flux over a lunation, we find that there are some local cavities on the implantation flux map, which are colocated with both the magnetic anomalies and the lunar swirls. Further studies show that there is a south–north asymmetry in the implantation flux, which can be used to explain the lower water content observed in the southern hemisphere. Our results provide a global map of the solar wind implantation flux on the lunar surface and are useful for evaluating the large-scale effect of solar wind implantation and sputtering on the space weathering and the water or gas generation of the surface.

Laboratory Modelling of Solar Wind Interaction with Lunar Magnetic Anomalies

The paper presents the results of laboratory experiment modeling the interaction between Lunar magnetic anomalies and Solar wind. To model the LMA we use quadrupole magnetic field. The main dimensionless parameter of the problem, the ion inertia length relative to the mini-magnetosphere size, well corresponds between experiment and LMA conditions. The main result is measurement of the magnetically reflected proton fluxes, which show qualitative agreement to available satellite data.

Laboratory Modelling of Solar Wind Interaction with Lunar Magnetic Anomalies

The paper presents results of laboratory experiment modeling the interaction between Lunar magnetic anomalies and Solar wind. To model the LMA we use quadrupole magnetic field. The main dimentionless parameter of the problem, the ion inertia length relative to the mini-magnetosphere size, well corresponds between experiment and LMA conditions. The main result is measurement of the magnetically reflected proton fluxes, which show qualitative agreement to available satellite data.

Lunar Magnetic Anomalies and Polar Ice

AbstractSolar wind ion sputtering is one of several non‐negligible loss mechanisms for water ice in permanently shadowed regions (PSRs) near the lunar poles. Previous estimates of the solar wind ion flux within south polar PSRs have considered only the ambient solar wind flow and effects of topography. Here, improved maps of crustal magnetic fields in the lunar polar regions are constructed, confirming that more anomalies are present near the south pole than near the north pole. These anomalies have moderate amplitudes, occur over at least two permanently shadowed craters, and correlate approximately with the exposed water ice distribution. Because of the low angle of solar wind incidence near the poles, these anomalies are likely effective in reducing the ion flux, and any resulting water ice loss rate. These anomalies may therefore explain why more water ice is found near the south pole than near the north pole.

On the Possibility of Excitation of Drift Instability in the Regions of Lunar Magnetic Anomalies

On the Possibility of Excitation of Drift Instability in the Regions of Lunar Magnetic Anomalies

Multipoint Observation of the Solar Wind Interaction with Strong Lunar Magnetic Anomalies by ARTEMIS Spacecraft and Chang’E-4 Rover

A shock or a mini-magnetosphere was once thought to be formed by the solar wind interaction with strong lunar magnetic anomalies. However, the full structure of a mini-magnetosphere has never been verified and whether a mini-magnetosphere can be completely formed remains a controversy. In this work, we present a unique multipoint observation of such an interaction by the ARTEMIS spacecraft and the Chang’E-4 rover. Both solar wind deceleration and penetration are observed by the Chang’E-4 rover on the lunar surface near the magnetic anomaly. Meanwhile, a shock is observed by the ARTEMIS spacecraft downstream from the magnetic anomaly. It is suggested that the magnetic anomaly cannot stand off the solar wind, and there is no shock but just a boundary layer near the magnetic anomaly. Accordingly, a mini-magnetosphere is not completely formed and the downstream shock observed the ARTEMIS spacecraft just corresponds to a trailing shock.

Dust Rotation and Swirl Morphology in Lunar Magnetic Anomalies

The scattering of light off the bright regions of lunar swirls suggests a relatively higher fraction of fine-grained dust compared to dust with similar optical maturity values found elsewhere on the lunar surface when assuming an isotropically oriented dust distribution, without preferred grain orientation. Here we propose a mechanism by which the ferromagnetic lunar fines, lofted by electrostatic effects or by meteoroid impacts, may rotate in a lunar magnetic anomaly and, upon landing, produce patches of organized alignments, generating anisotropic surface structures. We simulate these rotations for Reiner Gamma and provide a proof of concept for such a dust rotation model. While the magnetic forces remain negligibly small to influence the trajectories of the lofted particles, the magnetic torques have a significant effect on the rotation of magnetized dust, and can generate an organized landing pattern for elongated lunar fines, which offers a possible explanation for the lunar albedo patterns.

A Meandering Lunar Wake Produced by the Pickup of Reflected Solar‐Wind Ions

AbstractBy establishing two solar‐wind convection electric field‐associated coordinate systems, the magnetic and plasma properties in the lunar wake are examined. In the plane perpendicular to the interplanetary magnetic field, all the properties exhibit asymmetric distributions related to the electric field, and they are even periodically modulated every two lunar radii but only along the flank which the electric field points to. Evidences show that the solar‐wind ions, reflected over the dayside lunar magnetic anomalies, have produced these asymmetries and periodical modulations. These ions, undergoing both the electric drift and large‐radius gyration, bypass the Moon body and periodically penetrate into the wake flank, during which they exchange momentum with the refilling solar‐wind plasma, thereby resulting in the oscillations of the plasma and the periodical modulations of the wake.

Laboratory Simulation of Solar Wind Interaction with Lunar Magnetic Anomalies

Laboratory Simulation of Solar Wind Interaction with Lunar Magnetic Anomalies

Energetic Neutral Atom Distribution on the Lunar Surface and Its Relationship with Solar Wind Conditions

Abstract The Advanced Small Analyzer for Neutrals (ASAN) on board the Chang’E-4 Yutu-2 rover first detected energetic neutral atoms (ENAs) originating from the lunar surface at various lunar local times on the lunar farside. In this work, we examine the ENA energy spectra, obtained in the first 23 lunar days from 2019 January 11 to 2020 October 12, and find a higher ENA differential flux on the lunar dawnside than on the duskside. Combined with Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) data, we analyze the correlation between the ENA differential flux and solar wind parameters, such as flux, density, dynamic pressure, and velocity, for each ASAN energy channel on the dawnside and duskside. The results show that ENA differential flux is positively correlated with solar wind flux, density, and dynamic pressure and relatively lower on the duskside than on the dawnside. To determine the relationship between solar wind energy and ENA energy, we analyze the correlation between solar wind energy and ENA cutoff energy and temperature on the dawnside and duskside. The results show that the ENA cutoff energy and temperature are lower on the duskside than on the dawnside at the same solar wind energy. The difference between the ENA–solar wind observation on the dawnside and duskside is possibly caused by solar wind deflection and deceleration on the duskside, which can be attributed to the interaction between solar wind and the lunar magnetic anomalies located nearby in the northwestern direction of the Chang’E-4 landing site.

ULF Waves Observed by Lunar Prospector

AbstractWe have studied the spatial distribution of ultra‐low frequency (ULF) in the vicinity of the Moon using Lunar Prospector (LP) magnetometer data obtained at ∼100 km altitude during the period from February 20, 1998 to November 30, 1998. The lunar ULF waves are mostly identified over a broad frequency range of 10–60 mHz in the spacecraft frame. The occurrence rate of the ULF wave is high on the dayside above strong magnetic anomalies and depends on the interplanetary magnetic field orientation. We examine wave properties including the wave propagation direction and polarization. They are very similar to Kaguya observations, indicating that the ULF waves observed at LP and Kaguya are generated by the same mechanism. Although lunar ULF waves are commonly observed on the dayside above lunar magnetic anomalies, how they are established as a regular oscillation is not completely understood. In the present study, we suggest that the electromagnetic ion beam instability, driven by protons reflected from lunar magnetic anomalies, is the likely source of ULF waves observed at LP.

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

AbstractThe 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.

Whistler Wings and Reflected Particles During Solar Wind Interaction of Lunar Magnetic Anomalies

AbstractThe solar wind interaction of small‐scale lunar magnetic anomalies remains unsolved due to lack of in situ observations. A dedicated coordinate system is established here to reconstruct the distributions of two remotely sensed symptoms of this interaction: the low‐frequency whistlers and reflected protons. It is found that these whistlers form a pair of wings beside the Moon and they originate from the low‐altitude interaction region, instead of from the higher altitudes where the reflected protons arrive and the associated shocks possibly form. Electrons and protons may behave differently in the interaction region. The incident electrons remain in a fluid state and may be diverted by the anomalies, exciting the low‐frequency whistlers. The protons, however, become unmagnetized and are reflected specularly by the vertical electric fields. These electric fields may derive from the charge separation/different motions of the electrons and protons, although the presence of low‐altitude shocks cannot be ruled out completely.

Electrostatic Waves and Electron Heating Observed Over Lunar Crustal Magnetic Anomalies

AbstractAbove 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.

Evidence for an Ancient Near‐Equatorial Lunar Dipole From Higher Precision Inversions of Crustal Magnetization

AbstractStudies of lunar paleopoles have been used to make a variety of inferences about past episodes of true polar wander and the orientation of the ancient dynamo field. However, the large and variable uncertainties commonly reported for such studies make robust conclusions difficult. To make further progress, we used synthetic magnetic anomalies to assess a common method to estimate magnetization direction uncertainty. We find that with this method, magnetic anomalies with higher inclinations have systematically higher uncertainties than lower inclination anomalies. We call this effect inclination bias. A similar effect is found for declination, but it is weaker. We also find that this method often produces overly conservative uncertainty estimates. To avoid these effects, we use Monte Carlo methods to determine magnetization direction uncertainty. We apply our methods to five lunar magnetic anomalies with a wide range of reported magnetization directions and paleopole locations. We find that inclination bias partly explains the previously reported anomalously high and low direction uncertainties for two of these anomalies: Reiner Gamma and Airy. Our more robust uncertainties allow us to conclude that four paleopoles are located near the equator. Such low latitudes cannot be explained by true polar wander inferred from other independent datasets, such as the lunar gravity field and the polar hydrogen distribution. This in turn implies that the dynamo axis was once offset from the spin axis.