Other
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.5614b&link_type=abstract
American Astronomical Society, DPS meeting #38, #56.14; Bulletin of the American Astronomical Society, Vol. 38, p.587
Other
Scientific paper
The viscosity of water ice I is grain size- and temperature-dependent at conditions appropriate for the interiors of convecting ice I shells in large icy satellites such as Ganymede, Callisto, and Titan. Grain sizes within these bodies are not well-constrained, which hampers detailed modeling of their thermal and tectonic evolution. Terrestrial ice sheets experience temperatures and stresses similar to convecting ice shells within large satellites, so measurements of grain size and characterization of the processes that control it can provide insight into grain size in icy satellite interiors. Using methods developed in Barr and McKinnon (submitted), we provide an upper limit on grain size assuming it is controlled by dynamic recrystallization ( 10 cm) and a lower limit on grain size assuming it is controlled by the presence of non-water-ice impurities that inhibit grain growth ( 1 mm). Callisto possesses the warmest surface ( 130 K), and convection in an ice shell with dynamic recrystallization is possible for ice shells thicker than 50 km. This estimate takes into account both temperature-dependent ice conductivity and shell curvature. The polar regions of Ganymede and Titan's surface are substantially cooler, and sustained convection with dynamic recrystallization is only possible there in much thicker shells (or if the ice is weakened by other components). If these bodies initially formed with deep oceans, as is often supposed, impurities may be excluded from the ice shells, leading to large grains and difficulty initiating convection. If, on the other hand, the ice shell solidifies rapidly and incorporates soluble ions and silicate particles, early convection is more likely. In either case, for Ganymede it is most likely that convection would have begun near the equator, and spread to the satellite's poles as its ice shell thickened. This work is supported by a NASA OPR grant.
Barr Amy Courtright
McKinnon William B.
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