Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0424c&link_type=abstract
American Astronomical Society, DPS meeting #28, #04.24; Bulletin of the American Astronomical Society, Vol. 28, p.1075
Astronomy and Astrophysics
Astronomy
2
Scientific paper
During its first encounter with Ganymede, the Galileo spacecraft discovered that this moon has a significant, internal magnetic field. The surface field strength is estimated to be approximately 600 nT [Kivelson, et al. this meeting]. We argue that this could be the result of remanent magnetism within Ganymede's rocky core. Based on previous models of the core [Mueller and McKinnon, 1988], its composition includes 7.5 - 16% magnetite, a mineral which may hold strong remanent magnetism. On Earth, a magnetization per unit volume of 10,000 Amp/m is typical in magnetite ores. To first order, remanent magnetization scales linearly with magnetite concentration and the strength of the background magnetic field. If a significant fraction of Ganymede's core cooled through the Curie temperature (870 K for magnetite at 20 kbars pressure) at time when the background, Jovian magnetic field was greater than 110 nT, the Galileo observations can be explained by remanent magnetism. At Ganymede's current orbit, the steady component of the Jovian background field is approximately 130 nT. This value may have been substantially greater in the past, due to tidal evolution of Ganymede's orbit. If a similar mechanism applies to Callisto, we predict a surface field strength of under 120 nT.
Bagenal Fran
Crary Frank J.
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