Mars [Acuña et al., 1999] and the Moon [Fuller, 1974] have permanently magnetized patches of rock on their surfaces, suggesting that even if they now lack a dynamo field, at some time in the past they might have possessed one. That would agree with the giant volcanoes (apparently extinct) observed on Mars, which suggest a hot interior, although the volcanoes themselves are not associated with magnetic patches. On Mars, in particular, these patches (as observed by the Mars Global Surveyor) create fields about 20 times stronger than the surface magnetization of Earth (as distinct from the Earth's core magnetic field) would create at the same distance of observation.
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momijizukamori
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Date: 2006-06-11 12:50 am (UTC)Mars [Acuña et al., 1999] and the Moon [Fuller, 1974] have permanently magnetized patches of rock on their surfaces, suggesting that even if they now lack a dynamo field, at some time in the past they might have possessed one. That would agree with the giant volcanoes (apparently extinct) observed on Mars, which suggest a hot interior, although the volcanoes themselves are not associated with magnetic patches. On Mars, in particular, these patches (as observed by the Mars Global Surveyor) create fields about 20 times stronger than the surface magnetization of Earth (as distinct from the Earth's core magnetic field) would create at the same distance of observation.
From http://www.phy6.org/earthmag/mill_8.htm