Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5902b&link_type=abstract
American Astronomical Society, DPS meeting #40, #59.02; Bulletin of the American Astronomical Society, Vol. 40, p.505
Astronomy and Astrophysics
Astronomy
Scientific paper
Ganymede maintains a strong, intrinsically produced magnetic field, making it unique among the satellites of the Solar System. The field is likely generated by dynamo action within Ganymede's metallic core, but how a dynamo has been maintained into the current epoch remains unclear. Using a multi-layer, one-dimensional thermal model we find that present-day magnetic field production can only occur if the sulfur content of Ganymede's core is either very low or very high and the mantle can cool rapidly (i.e. its effective viscosity is similar to wet olivine). Because these requirements are not necessarily compatible with cosmochemical and physical models of the satellite we have explored an alternate scenario in which passage through a Laplace-like resonance in Ganymede's past enabled present-day magnetic field production. During resonance passage, tidal dissipation in the silicate mantle prevents the metallic core from cooling. Once the satellites escape the resonance, dissipation ends and the hot silicate mantle and metallic core cool rapidly, triggering convection in the core and generating a magnetic dynamo. To test the feasibility of this scenario we couple our thermal model to an orbital model of the Galilean satellites’ evolution into the Laplace resonance, which permits investigation of passage through one or more Laplace-like resonances that cause tidal heating in Ganymede. Contrary to expectations, we find that there are no physically plausible scenarios that permit sufficient tidal heating to maintain Ganymede's silicate mantle temperatures high enough for core convection to be triggered after the resonance ends. These results are robust to variations in silicate rheology, tidal dissipation factor of Jupiter, structure of the ice shell, and inclusion of partial melting in the silicates. Past resonance passage therefore appears unable to enable Ganymede's present-day magnetic field and alternate mechanisms must be sought. This work was supported by NASA PG&G and NESSF.
Bland Michael T.
Showman Adam P.
Tobie Gabriel
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