The Global Expansion and Resurfacing of Ganymede

Details The Global Expansion and Resurfacing of Ganymede The Global Expansion and Resurfacing of Ganymede

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p13f..02b&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P13F-02

Physics

5422 Ices, 5430 Interiors (8147), 5455 Origin And Evolution, 5475 Tectonics (8149), 6222 Ganymede

Scientific paper

Ganymede's surface is dominated by relatively young, extensional tectonic deformation. While it is generally accepted that this deformation formed during global expansion of the satellite, the cause of the expansion remains unclear. Here we investigate the feasibility of a scenario in which global expansion was caused by extensive melting of Ganymede's ice shell during the Galilean satellites' passage through a Laplace-like resonance. The current Laplace resonance does not pump Ganymede's eccentricity. However, Malhotra (1991) and Showman and Malhotra (1997) showed that the Galilean satellites may have passed through Laplace-like resonances that did force Ganymede's eccentricity, leading to internal heating of the satellite. Showman et al. (1997) explored the effects of such tidal heating on Ganymede and found that it can lead to thermal runaway, melting, and global expansion, helping to explain the extensive resurfacing of the satellite. While the likelihood of thermal runaway appeared small, improved understanding of the internal structure of Ganymede and the nature of stagnant lid convection warrants a new study. Here we present simulations of Ganymede's coupled thermal and orbital evolution. The orbital model allows a dynamical investigation of the orbital histories of the Galilean satellites near the observed 2:1 mean motion resonance. The thermal model simultaneously solves the energy balance in Ganymede's ice shell, silicate mantle, and Fe/FeS core. Stagnant lid convection, radiogenic heating, ocean formation, and inner core growth are included in the model. Additionally, we investigate the effect partial melting has on the thermal evolution of the ice shell. Coupling between the orbital and thermal models occurs via tidal dissipation, which is calculated with the model of Tobie et al. 2005 to determine how tidal heating is distributed throughout the satellite interior. These simulations reveal that passage through the Laplace-like resonance can lead to melting under a much broader range of initial conditions than suggested by Showman et al. (1997). The degree to which melting occurs is sensitive to the grain size of the ice and the assumed convective stress. The generation of melt would not only lead to satellite expansion and extensional stress, but would also provide a source of near surface melt, permitting cryovolcanic activity. It therefore appears plausible that resonance passage may have significantly contributed to the resurfacing of Ganymede.

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