Physics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.525r&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 525
Physics
1
Asteroids, Magnetization, Solar Wind, Wind Effects, Cooling, Galileo Spacecraft, Regolith, Remanence, Shock Wave Interaction
Scientific paper
Kivelson et al. have interpreted a reversal of magnetic field direction in the solar wind as the Galileo spacecraft encountered Gaspra as a shock front produced by the asteroid. The obstacle it presents to the solar wind has to be much greater than its dimensions and this is interpreted as a magnetic field. The inferred intensity of magnetization is in the range observed in meteorites. While small bodies such as chondrules and perhaps some meteorites may acquire a thermoremanent magnetization from the solar nebula magnetic field as they cool, it is unlikely that the spin axis of larger bodies could have remained fixed relative to the magnetic field for a sufficient time. Thus the question arises whether Gaspra's magnetization was acquired while it was in a parent body with a magnetic field. In a small accreted body heated by Al-26 an Fe core of about 100 km diameter could have formed that produced a magnetic field by dynamo action. The recent discovery of evidence for Fe-60 in the early solar system suggests that an Fe core could have remained molten and vigorously convecting for some million years, generating a mean field along its axis of rotation and therefore in a direction fixed with respect to the proto-Gaspra in its mantle. For it to acquire remnant magnetization it has to cool through the Curie point to low temperature while the field is present. Asteroids might cool quickly to 10 km depth if these were removed by collisions, and a protoasteroid in this outer shell could then become uniformly magnetized.
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