Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mbns.conf...26h&link_type=abstract
The Moon Beyond 2002: Next Steps in Lunar Science and Exploration, p. 26
Astronomy and Astrophysics
Astronomy
Lunar Magnetic Fields, Lunar Evolution, Lunar Core, Magnetic Anomalies, Astronomical Models, Planetary Mapping, Lunar Geology, Ejecta
Scientific paper
Current unresolved issues relating to the origin and interpretation of lunar paleomagnetism include: (1) the existence and size of a lunar metallic core; (2) the existence and temporal duration of a former core dynamo; (3) the role of impact plasmas in generating and/or modifying lunar magnetizing fields; (4) the origin of swirl-like albedo markings that correlate with the strongest individual orbital anomalies; and (5) the sources of magnetic anomalies on the far side in regions antipodal to major impact basins. A prerequisite for a former lunar core dynamo field is a metallic core. Conversely, if a former core dynamo is shown to be required by lunar paleomagnetic data, then the existence of a metallic core would be assured, with important implications for lunar origin and evolution models. At present, a number of geophysical constraints strongly suggest, but do not absolutely require, a metallic core with a radius in the range of 300 to 400 km. The most direct method for resolving the core issue is to analyze new seismic data such as that which may be obtained by the Lunar A mission. However, we emphasize here the possibility of analyzing orbital paleomagnetic data to investigate the existence of a former core dynamo and, indirectly, the existence of a metallic core. Specifically, modeling studies of relatively isolated orbital anomalies can yield estimates for bulk directions of magnetization for major anomaly sources. These directions of magnetization can be used to test the hypothesis that the lunar magnetizing field was dipolar and centered in the Moon, as expected for a core dynamo (issue (2) above). At the same time, inferred directions of magnetization for ejecta units such as the Cayley Formation, which are associated with a single basin-forming impact, can be used to investigate the role of impact plasmas in modifying or generating transient magnetizing fields (issue (3) above). Finally, correlative studies of orbital anomalies with surface geology can investigate the time period when lunar magnetizing fields were strongest.
Hood Lon L.
Richmond Nicola C.
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