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The Magnetic Dichotomy of the Galilean Satellites Europa and Ganymede

Breuer, D. and Hussmann, H. and Spohn, T. (2006) The Magnetic Dichotomy of the Galilean Satellites Europa and Ganymede. In: Eos Trans. AGU Fall Meeting suppl., 87 (52), P31D-04. American Geophysical Union Fall Meeting 2006, 2006-12-11 - 2006-12-15, San Francisco (USA).

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Abstract

AB: A major discovery of the Galileo mission was the detection of Ganymede's self-generated magnetic field. The magnetic field also proves beyond doubt that Ganymede is fully differentiated into an iron-rich core, a silicate mantle, and an outer ice shell that most likely also contains an ocean. It is widely believed that Europa has a similar structure although the absence of a self-sustained magnetic field makes the case for a core in Europa less compelling. Since Callisto's moment-of-inertia factor suggests an undifferentiated satellite and since the absence of a magnetic of Io is best explained by tidal heating in the mantle blocking the heat flow from the core (Wienbruch and Spohn, 1995), Europa and Ganymede form a magnetic dichotomy in the Jovian system. We have used stagnant lid models of convection in the two icy satellites to calculate thermal history models with core cooling and have allowed for inner core growth through freezing. The models have stagnant lid convection or conduction in the outer ice shells (depending on material parameters), isothermal oceans, and, in the case of Ganymede, stagnant-lid convection in the ice shell underneath the ocean and above the rock mantle. For Europa the ocean interfaces with the rock mantle. We assume iron cores that start fully molten for both satellites, the radii of which were taken from Sohl et al. (2002). These models suggest that Europa has a few 100 km smaller core and thinner mantle and a substantially thinner ice shell. All but interior structure parameters equal, we find that core convection and hence dynamo action is more likely for Europa than for Ganymede. The reason are mainly the larger core and the thicker mantle. Accepting core convection in Ganymede, the question than poses itself of how to explain the absence of core convection in Europa. We find and will discuss the following possibilities: 1) Europa has no iron core. This is consistent with the observation but leaves the question why Ganymede should have fully differentiated while Europa did not. 2) A higher concentration of light elements in Europa's core. Taking Sulfur as a point in case, Europa may have more sulfur, in which case more cooling would be required to freeze the core, or may even be on the FeS rich side of the eutectic, in which case chemical convection could be less efficient in Europa. 3) Tidal heating. We find that a few times the present-day radiogenic heating rate would be required to possibly frustrate dynamo action. This much tidal heat is consistent with the models of Hussmann et al. (2002) Hussmann, H. et al., 2002.

Document Type:Conference or Workshop Item (UNSPECIFIED)
Title: The Magnetic Dichotomy of the Galilean Satellites Europa and Ganymede
Authors:
AuthorsInstitution or Email of Authors
Breuer, D.UNSPECIFIED
Hussmann, H.Institut of Planetology, Wilhelm-Klemm Str. 10, Münster, 48149 Germany
Spohn, T.UNSPECIFIED
Date:December 2006
Journal or Publication Title:Eos Trans. AGU Fall Meeting suppl.
Volume:87
Page Range:P31D-04
Series Name:Eos Transactions AGU
Keywords:Core processes, Magnetic fields and magnetism, Origin and evolution, Europa, Ganymede
Event Title:American Geophysical Union Fall Meeting 2006
Event Location:San Francisco (USA)
Event Type:international Conference
Event Dates:2006-12-11 - 2006-12-15
Organizer:AGU
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben Vergleichende Planetologie (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Deposited By: Stefanie Musiol
Deposited On:15 Jan 2007
Last Modified:27 Apr 2009 13:25

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