Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander
A number of magnetic anomalies are present along the northern edge of the lunar South Pole-Aitken(SPA) basin. A variety of hypotheses for their formation have been proposed, but an in-depth study of their properties has not been performed. Here we use two different methods to invert for their source...
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ftdtic:AD1034491 2023-05-15T18:22:04+02:00 Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander Nayak,Michael Hemingway,Doug Garrick-Bethell,Ian AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB 2016-10-14 text/html http://www.dtic.mil/docs/citations/AD1034491 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD1034491 en eng http://www.dtic.mil/docs/citations/AD1034491 Approved For Public Release; Astronomy Electricity and Magnetism MAGNETIZATION Moon magnetic fields magnetic materials magnetic moments magnetometers planetary sciences magnetic anomalies angular momentum dikes Impact processes spa(South Pole-Aitken) hydrogen deposits paleopoles sesquinary impactors Text 2016 ftdtic 2018-01-07T15:51:11Z A number of magnetic anomalies are present along the northern edge of the lunar South Pole-Aitken(SPA) basin. A variety of hypotheses for their formation have been proposed, but an in-depth study of their properties has not been performed. Here we use two different methods to invert for their source body characteristics: one that completely searches a small parameter space of less than ten uniform strength dipoles per anomaly, and another that uses grids of hundreds of dipoles with variable magnetization strengths. Both methods assume uniform magnetization directions at each anomaly and with one exception, produce nearly the same results. We introduce new Monte Carlo methods to quantify errors in our inversions arising from Gaussian time-dependent changes in the external field and the uncertain geometry of the source bodies. We find the errors from uncertainty in source body geometry are almost always higher. We also find a diverse set of magnetization directions around SPA, which we combine with other physical arguments to conclude that the source bodies were likely magnetized in a dynamo field. Igneous intrusions are a reasonable explanation (Purucker et al., 2012) for the directional variability, since they could be intruded over different magnetic epochs. However, the directional variability also implies either surprisingly large amounts of true polar wander or a dynamo not aligned with the lunar spin axis. We also explore the possibility that true polar wander caused by the SPA impact could allow iron-rich SPA ejecta to record a diverse set of magnetic field directions. Some of this material may have also become sesquinary ejecta and re-impacted across the Moon on 10 4 10 6 year timescales to capture such changes. No completely satisfactory answer emerges, except that the dipole-axis of the lunar dynamo may have been variable in direction. Icarus, 286, 01 Jan 0001, 01 Jan 0001 Text South pole Defense Technical Information Center: DTIC Technical Reports database Aitken ENVELOPE(-44.516,-44.516,-60.733,-60.733) South Pole |
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Open Polar |
collection |
Defense Technical Information Center: DTIC Technical Reports database |
op_collection_id |
ftdtic |
language |
English |
topic |
Astronomy Electricity and Magnetism MAGNETIZATION Moon magnetic fields magnetic materials magnetic moments magnetometers planetary sciences magnetic anomalies angular momentum dikes Impact processes spa(South Pole-Aitken) hydrogen deposits paleopoles sesquinary impactors |
spellingShingle |
Astronomy Electricity and Magnetism MAGNETIZATION Moon magnetic fields magnetic materials magnetic moments magnetometers planetary sciences magnetic anomalies angular momentum dikes Impact processes spa(South Pole-Aitken) hydrogen deposits paleopoles sesquinary impactors Nayak,Michael Hemingway,Doug Garrick-Bethell,Ian Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
topic_facet |
Astronomy Electricity and Magnetism MAGNETIZATION Moon magnetic fields magnetic materials magnetic moments magnetometers planetary sciences magnetic anomalies angular momentum dikes Impact processes spa(South Pole-Aitken) hydrogen deposits paleopoles sesquinary impactors |
description |
A number of magnetic anomalies are present along the northern edge of the lunar South Pole-Aitken(SPA) basin. A variety of hypotheses for their formation have been proposed, but an in-depth study of their properties has not been performed. Here we use two different methods to invert for their source body characteristics: one that completely searches a small parameter space of less than ten uniform strength dipoles per anomaly, and another that uses grids of hundreds of dipoles with variable magnetization strengths. Both methods assume uniform magnetization directions at each anomaly and with one exception, produce nearly the same results. We introduce new Monte Carlo methods to quantify errors in our inversions arising from Gaussian time-dependent changes in the external field and the uncertain geometry of the source bodies. We find the errors from uncertainty in source body geometry are almost always higher. We also find a diverse set of magnetization directions around SPA, which we combine with other physical arguments to conclude that the source bodies were likely magnetized in a dynamo field. Igneous intrusions are a reasonable explanation (Purucker et al., 2012) for the directional variability, since they could be intruded over different magnetic epochs. However, the directional variability also implies either surprisingly large amounts of true polar wander or a dynamo not aligned with the lunar spin axis. We also explore the possibility that true polar wander caused by the SPA impact could allow iron-rich SPA ejecta to record a diverse set of magnetic field directions. Some of this material may have also become sesquinary ejecta and re-impacted across the Moon on 10 4 10 6 year timescales to capture such changes. No completely satisfactory answer emerges, except that the dipole-axis of the lunar dynamo may have been variable in direction. Icarus, 286, 01 Jan 0001, 01 Jan 0001 |
author2 |
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB |
format |
Text |
author |
Nayak,Michael Hemingway,Doug Garrick-Bethell,Ian |
author_facet |
Nayak,Michael Hemingway,Doug Garrick-Bethell,Ian |
author_sort |
Nayak,Michael |
title |
Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
title_short |
Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
title_full |
Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
title_fullStr |
Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
title_full_unstemmed |
Magnetization in the South Pole-Aitken basin: Implications for the lunar dynamo and true polar wander |
title_sort |
magnetization in the south pole-aitken basin: implications for the lunar dynamo and true polar wander |
publishDate |
2016 |
url |
http://www.dtic.mil/docs/citations/AD1034491 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD1034491 |
long_lat |
ENVELOPE(-44.516,-44.516,-60.733,-60.733) |
geographic |
Aitken South Pole |
geographic_facet |
Aitken South Pole |
genre |
South pole |
genre_facet |
South pole |
op_relation |
http://www.dtic.mil/docs/citations/AD1034491 |
op_rights |
Approved For Public Release; |
_version_ |
1766201422931558400 |