東華大學圖書館 |

Evolution of the Lunar Dynamo /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Evolution of the Lunar Dynamo // Ji-In Jung.
Author:	Jung, Ji-In,
Description:	1 electronic resource (208 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 87-02, Section: B.
Contained By:	Dissertations Abstracts International87-02B.
Subject:	Minerals. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32200973
ISBN:	9798288817618

Evolution of the Lunar Dynamo /
Jung, Ji-In,

Evolution of the Lunar Dynamo /Ji-In Jung. - 1 electronic resource (208 pages)

Source: Dissertations Abstracts International, Volume: 87-02, Section: B.

Planetary paleomagnetism provides a powerful window into the ancient magnetic fields and dynamo histories of terrestrial bodies such as Earth, the Moon, and Mars. Prior to the Apollo missions, the Moon was widely regarded as magnetically inert, largely due to the absence of detectable magnetic signals in early satellite observations (e.g., Luna 10, Explorer 35). This perception shifted dramatically with the return of Apollo samples, whose paleomagnetic analyses revealed a far more complex and long-lived history of the lunar magnetic field than previously imagined.The lunar dynamo is now thought to have initiated around ∼4.3 billion years ago (Ga), producing surface magnetic field intensities of ∼40 to 110 µT between approximately 3.9 Ga and 3.5 Ga (comparable to the strength of Earth's present-day magnetic field). Following this peak, the lunar magnetic field declined to ∼10-20 µT by ∼3.2 Ga and persisted in a weakened or potentially intermittent state (often termed the "low-field epoch") until it ceased entirely by around 0.9 Ga.Despite these findings, the mechanism responsible for sustaining such a strong and long-lived lunar dynamo remains poorly understood. The Moon's relatively small core is unlikely to support a thermochemically driven dynamo through conventional heat energy sources such as gravitational, differential, latent, or radiogenic heat. Consequently, a range of alternative power sources has been proposed, including thermocompositional convection and mechanical forcing from external processes such as massive impact events or precession. However, none of these mechanisms alone fully accounts for both the intensity and duration of the lunar magnetic field.Several recent paleomagnetic studies have even questioned the fundamental validity of earlier lunar paleointensity estimates. The observed magnetizations may instead reflect contamination from impact-generated plasma fields, spacecraft-induced magnetic fields, or other secondary overprints acquired long after the rocks originally formed. Further uncertainty arises from the intrinsic limitations of lunar magnetic carriers, which are known to be poor paleomagnetic recorders of remanent magnetization based on prior microscopic and rock magnetic analyses. As a result, whether the Moon ever sustained a global magnetic field-and, if so, which dynamo mechanisms operated during different stages of its magnetic history-remains one of the most compelling open questions in planetary science.This Ph.D. thesis integrates a series of studies that evaluate the fidelity of lunar magnetic records in order to address this central question.Chapter 1 explores the potential variability of the lunar magnetic field during the high-field epoch (3.9-3.5 Ga). Apollo samples from this time interval that exhibit low paleointensity values in the Apollo-era dataset were selected, and detailed paleomagnetic and rock magnetic analyses were conducted. This chapter was published in Earth and Planetary Science Letters under the terms of the Creative Commons License (https://creativecommons.org/licenses/by/4.0): Jung, J., Tikoo, S. M., Burns, D. H., V´aci, Z., Krawczynski, M. J. (2024), Assessing lunar paleointensity variability during the 3.9 - 3.5 Ga high field epoch. Earth and Planetary Science Letters, 638, 118757. https://doi.org/10.1016/j.epsl.2024.118757.Chapter 2 examines the magnetic recording capabilities of lunar rocks, which have traditionally been considered poor magnetic recorders. This chapter presents an extensive suite of microscopic (SEM and TEM) and rock magnetic experiments on diverse Apollo mare basalt samples to evaluate (1) their suitability for paleointensity estimation and (2) other possible magnetic carriers (e.g., iron oxides). This chapter is currently under revision: Jung, J., Tikoo, S. M., Burns, D. H., V´aci, Z., Krawczynski, M. J., Solheid, P., Burns, D. H. (in review), Magnetic mineralogy in lunar mare basalts and implications for paleointensity retrieval. Journal of Geophysical Research: Planets.Chapter 3 applies deep learning techniques to microscopic images for the automated identification of lunar mineral phases and basalt types. This framework is designed to support scalable petrological classification, potentially streamlining future assessments of lunar samples. This chapter is currently in preparation for submission to a peer-reviewed journal, under the title Automated mineral identification and rock classification in lunar mare basalts, with co-authors Tikoo, S. M., and Chung, J. The SEM image data were provided by Joy, C., Bell, S., Vaci, Z., and Day, J.Chapter 4 evaluates the effects of shock events and possible pressure demagnetization through controlled hydrostatic pressure experiments on Apollo samples. This chapter also integrates paleointensity data from both Apollo-era and modern studies to assess the global paleointensity variability of the lunar magnetic record. A manuscript titled The effect of shock demagnetization on lunar paleointensity records is currently in preparation for submission to a peer-reviewed journal, co-authored by Tikoo, S. M., Gattacceca, J., and Lepaulard, C.

English

ISBN: 9798288817618Subjects--Topical Terms:

542841
Minerals.
Subjects--Index Terms:

Lunar magnetic field

Evolution of the Lunar Dynamo /
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520 $a Planetary paleomagnetism provides a powerful window into the ancient magnetic fields and dynamo histories of terrestrial bodies such as Earth, the Moon, and Mars. Prior to the Apollo missions, the Moon was widely regarded as magnetically inert, largely due to the absence of detectable magnetic signals in early satellite observations (e.g., Luna 10, Explorer 35). This perception shifted dramatically with the return of Apollo samples, whose paleomagnetic analyses revealed a far more complex and long-lived history of the lunar magnetic field than previously imagined.The lunar dynamo is now thought to have initiated around ∼4.3 billion years ago (Ga), producing surface magnetic field intensities of ∼40 to 110 µT between approximately 3.9 Ga and 3.5 Ga (comparable to the strength of Earth's present-day magnetic field). Following this peak, the lunar magnetic field declined to ∼10-20 µT by ∼3.2 Ga and persisted in a weakened or potentially intermittent state (often termed the "low-field epoch") until it ceased entirely by around 0.9 Ga.Despite these findings, the mechanism responsible for sustaining such a strong and long-lived lunar dynamo remains poorly understood. The Moon's relatively small core is unlikely to support a thermochemically driven dynamo through conventional heat energy sources such as gravitational, differential, latent, or radiogenic heat. Consequently, a range of alternative power sources has been proposed, including thermocompositional convection and mechanical forcing from external processes such as massive impact events or precession. However, none of these mechanisms alone fully accounts for both the intensity and duration of the lunar magnetic field.Several recent paleomagnetic studies have even questioned the fundamental validity of earlier lunar paleointensity estimates. The observed magnetizations may instead reflect contamination from impact-generated plasma fields, spacecraft-induced magnetic fields, or other secondary overprints acquired long after the rocks originally formed. Further uncertainty arises from the intrinsic limitations of lunar magnetic carriers, which are known to be poor paleomagnetic recorders of remanent magnetization based on prior microscopic and rock magnetic analyses. As a result, whether the Moon ever sustained a global magnetic field-and, if so, which dynamo mechanisms operated during different stages of its magnetic history-remains one of the most compelling open questions in planetary science.This Ph.D. thesis integrates a series of studies that evaluate the fidelity of lunar magnetic records in order to address this central question.Chapter 1 explores the potential variability of the lunar magnetic field during the high-field epoch (3.9-3.5 Ga). Apollo samples from this time interval that exhibit low paleointensity values in the Apollo-era dataset were selected, and detailed paleomagnetic and rock magnetic analyses were conducted. This chapter was published in Earth and Planetary Science Letters under the terms of the Creative Commons License (https://creativecommons.org/licenses/by/4.0): Jung, J., Tikoo, S. M., Burns, D. H., V´aci, Z., Krawczynski, M. J. (2024), Assessing lunar paleointensity variability during the 3.9 - 3.5 Ga high field epoch. Earth and Planetary Science Letters, 638, 118757. https://doi.org/10.1016/j.epsl.2024.118757.Chapter 2 examines the magnetic recording capabilities of lunar rocks, which have traditionally been considered poor magnetic recorders. This chapter presents an extensive suite of microscopic (SEM and TEM) and rock magnetic experiments on diverse Apollo mare basalt samples to evaluate (1) their suitability for paleointensity estimation and (2) other possible magnetic carriers (e.g., iron oxides). This chapter is currently under revision: Jung, J., Tikoo, S. M., Burns, D. H., V´aci, Z., Krawczynski, M. J., Solheid, P., Burns, D. H. (in review), Magnetic mineralogy in lunar mare basalts and implications for paleointensity retrieval. Journal of Geophysical Research: Planets.Chapter 3 applies deep learning techniques to microscopic images for the automated identification of lunar mineral phases and basalt types. This framework is designed to support scalable petrological classification, potentially streamlining future assessments of lunar samples. This chapter is currently in preparation for submission to a peer-reviewed journal, under the title Automated mineral identification and rock classification in lunar mare basalts, with co-authors Tikoo, S. M., and Chung, J. The SEM image data were provided by Joy, C., Bell, S., Vaci, Z., and Day, J.Chapter 4 evaluates the effects of shock events and possible pressure demagnetization through controlled hydrostatic pressure experiments on Apollo samples. This chapter also integrates paleointensity data from both Apollo-era and modern studies to assess the global paleointensity variability of the lunar magnetic record. A manuscript titled The effect of shock demagnetization on lunar paleointensity records is currently in preparation for submission to a peer-reviewed journal, co-authored by Tikoo, S. M., Gattacceca, J., and Lepaulard, C.
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