Remanent Magnetization in Meteorites

Abstract

ALTHOUGH the existence of natural remanent magnetization in meteorites has been taken as evidence for a primaeval magnetic field in the original bodies—presumably of asteroidal dimensions—from which meteorites formed¹, it seems surprising that an asteroidal core (∼ 100 km diameter as an upper limit) can sustain convective motions efficient enough to produce the magnetic field, ∼ 10⁻¹ to 1 G, required by the NRM measurements². Moreover, recent data suggest that iron meteorites are not necessarily fragments of a much larger core, as had been supposed, but formed as small bodies embedded in a silicate matrix³. As there is no other obvious internal mechanism for generating NRM, could an external mechanism be responsible? During the early history of the solar system, the magnetic field of the Sun may have been much more intense than it is at present, possibly ∼ 100 G (ref. 4), and the rotation of the Sun may have been much more rapid. A recent estimate for solar spin damping by the solar wind gives an e-folding time ∼2.2×10⁹ yr (ref, 5). There are two mechanisms by which NRM could have been created in meteorites under these conditions.