HR: 1340h
AN: GP43A-0889    [Abstracts]
TI: Sulfur's impact on core evolution and magnetic field generation on Ganymede
AU: * Hauck, S A
EM: hauck@case.edu
AF: Case Western Reserve University Department of Geological Sciences, 10900 Euclid Avenue 112 AW Smith, Cleveland, OH 44106-7216 United States
AU: Aurnou, J M
EM: aurnou@ucla.edu
AF: University of California, Los Angeles Department of Earth and Space Sciences, 595 Charles Young Drive East Box 951567, Los Angeles, CA 90095-1567 United States
AU: Dombard, A J
EM: andrew.dombard@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11000 Johns Hopkins Rd, Laurel, MD 90095-1567 United States
AB: Analysis of the melting relationships of potential core forming materials in Ganymede indicate that convective motions capable of generating the satellite's magnetic field may be driven, in-part, either by iron "snow" forming below the core-mantle boundary or solid iron sulfide floating upward from the deep core. Eutectic melting temperatures in the binary Fe-FeS system decrease with increasing pressure over the interval of core pressures on Ganymede (<14 GPa). Comparison of melting temperatures to adiabatic temperature gradients in the core suggest that solid iron is thermodynamically stable at shallow levels for bulk core compositions more iron-rich than eutectic (i.e., <21 wt % S). Calculations based on high-pressure solid-liquid phase relationships in the Fe-FeS system indicate that Fe snow or floatation of solid FeS, depending on whether the core composition is more or less Fe-rich than eutectic, is an inevitable consequence of cooling Ganymede's core. Our results demonstrate that these conclusions are robust over a wide-range of plausible three-layer internal structures and thermal evolution scenarios. Using scaling arguments based on recent experimental work we estimate core Rossby and magnetic Reynolds numbers plausibly consistent with a dynamo being generated in Ganymede's core via Fe-snow. Depending on core composition, either shallow formation of Fe snow or deep precipitation and subsequent floatation of FeS is an important mechanism for driving the moon's strong internally-generated magnetic field.
DE: 5734 Magnetic fields and magnetism
DE: 6222 Ganymede
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005