Many planets,including the Earth,possess a global dipolar magnetic field.To diagnose the interior source of the dipolar field,researchers usually adopt a dipole model consisting of six parameters to fit the observed d...Many planets,including the Earth,possess a global dipolar magnetic field.To diagnose the interior source of the dipolar field,researchers usually adopt a dipole model consisting of six parameters to fit the observed dataset of the magnetic field.However,the simultaneous fitting of these parameters often leads to multiple local optimal parameter sets.To address this fitting dilemma,Rong ZJ et al.(2021)recently developed a current loop model.This technique can successively separate and invert the loop parameters.Here,we further show how this technique can be reduced and modified to fit a dipole model.Applications of this reduced technique to the International Geomagnetic Reference Field model and the Martian crustal field model highlight its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly,a capability that sets it apart from existing methods.The potential impact of this technique on geomagnetism and planetary magnetism is significant,given its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly.展开更多
The Moon currently lacks a global magnetic field;however,both paleomagnetic analyses of lunar rock samples and orbital magnetic measurements indicate that it once possessed a core dynamo.Magnetic field measurements of...The Moon currently lacks a global magnetic field;however,both paleomagnetic analyses of lunar rock samples and orbital magnetic measurements indicate that it once possessed a core dynamo.Magnetic field measurements of some datable impact basins suggest that the lunar core dynamo persists to the Nectarian period(~3.9 to 3.8 billion years ago Ga).Investigations of the Apollo samples using modern methods demonstrate that the field overall was active between 4.25 and 1.92 Ga.During the period prior to 3.56 Ga,the field was sometimes comparable to Earth’s but subsequently declined dramatically and ultimately ceased.Several hypotheses have been proposed to explain the dynamo generation and duration.Thermal convection in the lunar core could have provided dynamo energy for the first several hundred million years while core crystallization could have sustained the dynamo for up to 1.5 Ga.Other mechanisms,such as mantle and/or inner core precession,changes in the rotation rate of the lunar mantle caused by impacts,and a basal magma ocean,also hold the potential to power the dynamo during some time of lunar evolutionary history.Impacts related to plasmas are believed to be insufficient for crustal magnetization though they can amplify the pre-existing magnetic field before the impacts.This paper summarizes and reviews the current understanding of lunar magnetic field evolution,including paleomagnetic studies that quantify the timing of the lunar surface strength,global crustal magnetization features derived from recent global magnetic field models based on orbital magnetic measurements,and various models explaining the powering of a lunar dynamo,which can account for most observations.Finally,we propose the outstanding questions and offer guidance for future lunar exploration such as the Chang’E series and lunar scientific observatories.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42388101)the Key Research Program of the Chinese Academy of Sciences(Grant No.ZDBS-SSW-TLC00103)the Key Research Program of the Institute of Geology and Geophysics,Chinese Academy of Sciences(IGGCAS-202102).
文摘Many planets,including the Earth,possess a global dipolar magnetic field.To diagnose the interior source of the dipolar field,researchers usually adopt a dipole model consisting of six parameters to fit the observed dataset of the magnetic field.However,the simultaneous fitting of these parameters often leads to multiple local optimal parameter sets.To address this fitting dilemma,Rong ZJ et al.(2021)recently developed a current loop model.This technique can successively separate and invert the loop parameters.Here,we further show how this technique can be reduced and modified to fit a dipole model.Applications of this reduced technique to the International Geomagnetic Reference Field model and the Martian crustal field model highlight its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly,a capability that sets it apart from existing methods.The potential impact of this technique on geomagnetism and planetary magnetism is significant,given its unique ability to diagnose both the planetary global dipolar field and the local crustal field anomaly.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(grant No.XDB41010304)the National Natural Science Foundation of China(42374217,42274224,42030205,and 42241101)+2 种基金We acknowledge support from the National Key R&D Program of China(grant no.2022YFF0503200)the Key Research Program of the Chinese Academy of Sciences(grant nos.ZDBS-SSW-TLC001 and ZDBS-SSW-JSC007-3)the Key Research Programs of the Institute of Geology and Geophysics,Chinese Academy of Sciences(IGGCAS-202102 and IGGCAS-202101).
文摘The Moon currently lacks a global magnetic field;however,both paleomagnetic analyses of lunar rock samples and orbital magnetic measurements indicate that it once possessed a core dynamo.Magnetic field measurements of some datable impact basins suggest that the lunar core dynamo persists to the Nectarian period(~3.9 to 3.8 billion years ago Ga).Investigations of the Apollo samples using modern methods demonstrate that the field overall was active between 4.25 and 1.92 Ga.During the period prior to 3.56 Ga,the field was sometimes comparable to Earth’s but subsequently declined dramatically and ultimately ceased.Several hypotheses have been proposed to explain the dynamo generation and duration.Thermal convection in the lunar core could have provided dynamo energy for the first several hundred million years while core crystallization could have sustained the dynamo for up to 1.5 Ga.Other mechanisms,such as mantle and/or inner core precession,changes in the rotation rate of the lunar mantle caused by impacts,and a basal magma ocean,also hold the potential to power the dynamo during some time of lunar evolutionary history.Impacts related to plasmas are believed to be insufficient for crustal magnetization though they can amplify the pre-existing magnetic field before the impacts.This paper summarizes and reviews the current understanding of lunar magnetic field evolution,including paleomagnetic studies that quantify the timing of the lunar surface strength,global crustal magnetization features derived from recent global magnetic field models based on orbital magnetic measurements,and various models explaining the powering of a lunar dynamo,which can account for most observations.Finally,we propose the outstanding questions and offer guidance for future lunar exploration such as the Chang’E series and lunar scientific observatories.
