scholarly journals Was the moon magnetized by impact plasmas?

2020 ◽  
Vol 6 (40) ◽  
pp. eabb1475
Author(s):  
Rona Oran ◽  
Benjamin P. Weiss ◽  
Yuri Shprits ◽  
Katarina Miljković ◽  
Gábor Tóth
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Magnetic Anomalies ◽  
The Moon ◽  
Crustal Field ◽  
Impact Simulations ◽  
Magnetizing Field

The crusts of the Moon, Mercury, and many meteorite parent bodies are magnetized. Although the magnetizing field is commonly attributed to that of an ancient core dynamo, a longstanding hypothesized alternative is amplification of the interplanetary magnetic field and induced crustal field by plasmas generated by meteoroid impacts. Here, we use magnetohydrodynamic and impact simulations and analytic relationships to demonstrate that although impact plasmas can transiently enhance the field inside the Moon, the resulting fields are at least three orders of magnitude too weak to explain lunar crustal magnetic anomalies. This leaves a core dynamo as the only plausible source of most magnetization on the Moon.

Implications of magnetic secular variation for interpretation of crustal field anomalies

2020 ◽  
Author(s):  
Rick Saltus ◽  
Aaron Canciani ◽  
Brian Meyer ◽  
Arnaud Chulliat
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomalies ◽  
Source Inversion ◽  
Magnetic Minerals ◽  
The Earth ◽  
Crustal Field ◽  
Data Compilation ◽  
Initial Work ◽  
Navigation Accuracy ◽  
Changes Over Time

<p>We usually think of crustal magnetic anomalies as static (barring some major seismic or thermal disruption).  But a significant portion of the crustal magnetic field is caused by the interaction of magnetic minerals with the Earth’s magnetic field.  This induced magnetic effect is dependent on the direction and magnitude of the ambient field.  So, of course, as the Earth’s magnetic field changes over time, the form and magnitude of induced magnetic anomalies will vary as well.  These changes will often be negligible for interpretation when compared with measurement and other interpretational uncertainties.  However, with the reduction of various sources of measurement noise and increased fidelity of interpretation, these temporal anomaly changes may need to be considered.</p><p>In addition to considerations relating to interpretation uncertainty, these temporal anomaly changes, if they are measured in multiple magnetic epochs, can theoretically provide valuable information for use in source inversion.  For example, since crustal magnetic anomalies arise from a combination of induced (dependent the ambient field) and remanent (not dependent on ambient field) magnetic sources, measurements of secular magnetic variation can assist in separating these two sources during inversion.</p><p>We will report modeling of the expected form and magnitude of predicted induced anomaly variations, the possible implications of these variations for data compilation and interpretation, and on the availability of relevant data for measuring them.  Recent research into the use of high-resolution magnetic anomaly maps for airborne magnetic navigation has also brought the issue of changing magnetic fields into focus.  Initial work indicates that changes in induced anomalies could affect navigation accuracy in certain situations.</p>

scholarly journals Moon’s Magnetic Field May Magnetize Iron That Hits Its Surface

Eos ◽  
2018 ◽  
Vol 99 ◽  
Author(s):  
Sarah Witman
Keyword(s):  
Magnetic Field ◽  
Satellite Data ◽  
Magnetic Anomalies ◽  
Large Impact ◽  
The Moon ◽  
Impact Basins

Scientists are using satellite data to study large impact basins on the surface of the Moon that contain magnetic anomalies.

scholarly journals An event study on broadband electric field noises and electron distributions in the lunar wake boundary

2022 ◽  
Vol 74 (1) ◽  
Author(s):  
Masaki N. Nishino ◽  
Yoshiya Kasahara ◽  
Yuki Harada ◽  
Yoshifumi Saito ◽  
Hideo Tsunakawa ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Electric Fields ◽  
Lunar Surface ◽  
Electron Beams ◽  
The Moon ◽  
Link Type ◽  
Electron Distributions

AbstractWave–particle interactions are fundamental processes in space plasma, and some plasma waves, including electrostatic solitary waves (ESWs), are recognised as broadband noises (BBNs) in the electric field spectral data. Spacecraft observations in recent decades have detected BBNs around the Moon, but the generation mechanism of the BBNs is not fully understood. Here, we study a wake boundary traversal with BBNs observed by Kaguya, which includes an ESW event previously reported by Hashimoto et al. Geophys Res Lett 37:L19204 10.1029/2010GL044529 (2010). Focusing on the relation between BBNs and electron pitch-angle distribution functions, we show that upward electron beams from the nightside lunar surface are effective for the generation of BBNs, in contrast to the original interpretation by Hashimoto et al. Geophys Res Lett 37:L19204 10.1029/2010GL044529 (2010) that high-energy electrons accelerated by strong ambipolar electric fields excite ESWs in the region far from the Moon. When the BBNs were observed by the Kaguya spacecraft in the wake boundary, the spacecraft’s location was magnetically connected to the nightside lunar surface, and bi-streaming electron distributions of downward-going solar wind strahl component and upward-going field-aligned beams (at $$\sim$$ ∼ 124 eV) were detected. The interplanetary magnetic field was dominated by a positive $$B_Z$$ B Z (i.e. the northward component), and strahl electrons travelled in the antiparallel direction to the interplanetary magnetic field (i.e. southward), which enabled the strahl electrons to precipitate onto the nightside lunar surface directly. The incident solar wind electrons cause negative charging of the nightside lunar surface, which generates downward electric fields that accelerate electrons from the nightside surface toward higher altitudes along the magnetic field. The bidirectional electron distribution is not a sufficient condition for the BBN generation, and the distribution of upward electron beams seems to be correlated with the BBNs. Ambipolar electric fields in the wake boundary should also contribute to the electron acceleration toward higher altitudes and further intrusion of the solar wind ions into the deeper wake. We suggest that solar wind ion intrusion into the wake boundary is also an important factor that controls the BBN generation by facilitating the influx of solar wind electrons there. Graphical Abstract

Chang’E-1 observations of pickup ions near the Moon under different interplanetary magnetic field conditions

2013 ◽  
Vol 79-80 ◽  
pp. 56-63 ◽  
Author(s):  
J. Zhong ◽  
L. Xie ◽  
H. Zhang ◽  
J.X. Li ◽  
Z.Y. Pu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Field Conditions ◽  
The Moon ◽  
Pickup Ions

The early magnetic field and primeval satellite system of the Moon: clues to planetary formation

1994 ◽  
Vol 349 (1690) ◽  
pp. 181-196 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomalies ◽  
Satellite System ◽  
Iron Core ◽  
Planetary Formation ◽  
The Moon ◽  
The Core ◽  
Basin Formation ◽  
The Mean ◽  
The Moment

From the stable remanent magnetization of the Apollo igneous rocks and high-grade breccias the existence of a primeval lunar magnetic field was inferred. The palaeointensities of the samples rise rapidly to a maximum at 3.9 Ga, then decrease exponentially to 3.2 Ga, strongly suggesting that the Moon had a field generated in a core, the existence of which was inferred from its non-hydrostatic figure. Modelling of the Apollo 15 and 16 subsatellite magnetic anomalies, by P. J. Coleman, L. L. Hood and C. T. Russell, gave palaeomagnetic directions of crustal strata. This enabled N pole positions to be calculated, which were empirically found to form three bipolar groups, the mean poles of which define (on the core dynamo hypothesis) three axes of rotation different from the present. These were dated as Pre-Nectarian, Lower Nectarian, and Upper Nectarian-Imbrian. Multi-ring basins of these ages were found to lie close to the corresponding palaeo-equators. The impacting bodies were therefore satellites, not asteroids or comets. Their velocities, before collision, can be shown (from basin asymmetries) to be nearly equatorial. The consequent changes in the moment of inertia tensor by basin formation caused these successive reorientations of the Moon relative to its axis of rotation in space. The three mean poles form a 90° spherical triangle. The explanation is that the Moon had three satellites: the orbits of each decayed, they broke up at the Roche limit into smaller bodies, which produced impact basins near the equator. The Moon then reorientated according to Euler’s principle before the next group of impacts. Lunar palaeomagnetism, and especially the inferences that the Moon has an iron core that segregated late and had a primeval satellite system, may provide important constraints on theories of lunar and planetary formation.

Simulations of Magnetic Fields Produced by Asteroid Impact: Possible Implications for Planetary Paleomagnetism

2019 ◽  
Author(s):  
David A. Crawford
Keyword(s):  
Magnetic Field ◽  
Magnetic Measurements ◽  
Magnetic Anomalies ◽  
Iron Core ◽  
The Moon ◽  
Major Question ◽  
Asteroid Impact ◽  
Origin And Evolution ◽  
The Impact ◽  
The Magnetic Field

Abstract The origin and evolution of the Moon's magnetic field has been a major question in lunar science ever since Luna 1 made the first magnetic measurements in the vicinity of the Moon in 1959. Orbital measurements show that the magnetic field at the surface of the Moon has local scale lengths on the order of 1-100 km. While this could suggest a correlation with impact craters, most lunar magnetic anomalies don’t appear to correlate with known geologic structures, including impacts [1]. However, the magnetic field produced by impact events are spatially and temporally complex. Add in the complexity of remanence acquisition (localized regions of heating/cooling and/or shock that can produce remanence in the presence of a magnetic field) and we have the potential for a complex pattern to emerge. Wieczorek et al. [1] showed just how such complexity may play out. In their simulations, some lunar magnetic anomalies may be caused by regions of concentrated magnetic materials associated with fragments of the South Pole-Aitken impactor, especially if the impactor was differentiated with an iron core. More recently, Oliveira et al. [2] showed that magnetic anomalies associated with five large lunar basins may be caused by impact melt sheets that cooled in the presence of an early lunar dynamo. In this paper we will look at an alternative explanation for many lunar anomalies that doesn’t require the presence of a lunar dynamo. At least some lunar anomalies may be associated with a deeper, thicker yet more varied region of magnetization acquired by rocks that became hot and cooled rapidly enough during crater formation to have acquired the transient magnetic field produced by the impact itself.

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