Abstract
As part of our study of the larger-scale remanent magnetic field of the Moon, we have examined the effects of cratering in an otherwise spherically symmetrical shell magnetized by a concentric dipolar magnetic fieldH o to an intensity of magnetizationc H o, wherec is a constant. In our initial model, we assume that the material excavated from the craters is distributed with random orientation and thus does not contribute to the remanent dipole momentM g . We further assume that the mare fill does not contribute significantly toM g . We choose the magnetizing dipole momentM o and the constantc such that the magnitude of the productcH o ≃ 3 × 10−4Г at the outer surface of the shell in the equatorial plane of the dipole. This value of the intensity of remanent magnetization was chosen to be within the range 10−7−10−3Г’; the intensities of thermo-remanent magnetization exhibited by Apollo samples. Finally, we use the locations and diameters of the 10 largest craters on the Moon and the depth-to-diameter ratios of Pike’s formulation to model approximately the excavation of the magnetized shell.
The remanent dipole momentM g was calculated for each of three orthogonal orientations of the magnetizing dipoleM o. The three magnitudes ofM g fall in the range 4 × 1018−1 × 1019Г cm3 which is close to the upper limit of 1019Г cm3 estimated forM g from the field measurements obtained with the Apollo subsatellites. Further, the distribution of the craters is such as to produce a significant transverse component ofM g with acute angles between the spin axis andM g in the range 51°–77°.
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Weiss, H., Coleman, P.J. The moon’s permanent magnetic field: a cratered-shell model. The Moon 16, 311–315 (1977). https://doi.org/10.1007/BF02634578
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DOI: https://doi.org/10.1007/BF02634578