Central magnetic anomalies of Nectarian-aged lunar impact basins: Probable evidence for an early core dynamo

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55 Scopus citations

Abstract

A re-examination of all available low-altitude LP magnetometer data confirms that magnetic anomalies are present in at least four Nectarian-aged lunar basins: Moscoviense, Mendel-Rydberg, Humboldtianum, and Crisium. In three of the four cases, a single main anomaly is present near the basin center while, in the case of Crisium, anomalies are distributed in a semi-circular arc about the basin center. These distributions, together with a lack of other anomalies near the basins, indicate that the sources of the anomalies are genetically associated with the respective basin-forming events. These central basin anomalies are difficult to attribute to shock remanent magnetization of a shocked central uplift and most probably imply thermoremanent magnetization of impact melt rocks in a steady magnetizing field. Iterative forward modeling of the single strongest and most isolated anomaly, the northern Crisium anomaly, yields a paleomagnetic pole position at 81° ± 19°N, 143° ± 31°E, not far from the present rotational pole. Assuming no significant true polar wander since the Crisium impact, this position is consistent with that expected for a core dynamo magnetizing field. Further iterative forward modeling demonstrates that the remaining Crisium anomalies can be approximately simulated assuming a multiple source model with a single magnetization direction equal to that inferred for the northernmost anomaly. This result is most consistent with a steady, large-scale magnetizing field. The inferred mean magnetization intensity within the strongest basin sources is ∼1. A/m assuming a 1-km thickness for the source layer. Future low-altitude orbital and surface magnetometer measurements will more strongly constrain the depth and/or thicknesses of the sources.

Original languageEnglish (US)
Pages (from-to)1109-1128
Number of pages20
JournalIcarus
Volume211
Issue number2
DOIs
StatePublished - Feb 2011

Keywords

  • Magnetic fields
  • Moon
  • Moon, Interior

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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