Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13f..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P13F-04
Mathematics
Logic
[0456] Biogeosciences / Life In Extreme Environments, [6280] Planetary Sciences: Solar System Objects / Saturnian Satellites
Scientific paper
Enceladus exhibits a strong hemispheric dichotomy of tectonism and heat flux, with geologically young, heavily tectonized terrains and a high heat flux in the south polar terrains (SPT) and relatively ancient terrains with presumably lower heat fluxes over the rest of the satellite. To understand the conditions that can give rise to this dichotomy, we present three-dimensional numerical models of convection in Enceladus' ice shell including tidal heating. Our tidal heating formulation and thermal boundary conditions exhibit no north-south asymmetries, but because the tectonism at the SPT may weaken the ice there, we implement a mechanically weak lithosphere (parameterized by a reduced viscosity contrast) within the SPT. In the absence of such a weak zone, convection--if any--resides in stagnant-lid mode and exhibits no hemispheric dichotomy. When such a weak zone is included, however, a significant dichotomy develops between the northern and southern hemispheres. Outside the SPT, only stagnant lid convection, or no convection at all, occurs. In the ice underneath the SPT, however, the lithosphere is thin, and, assuming the ice grain size is sufficiently small, vigorous convective plumes rise close to the surface. Away from the SPT, our models exhibit a modest heat flux of only 5-10 mW/m^2, and the surface strains are small enough to imply surface ages of >1 Byr. Within the SPT, however, our models yield heat fluxes of of 70-200 mW/m^2, implying heat flows integrated across the SPT of up to 5 GW, similar to that inferred from Cassini thermal observations. The surface strains in our models are high enough near the south pole to cause intense tectonism and imply surface ages of 1 to 10 Myr, consistent with the young age estimates of the SPT. Thus, our models can explain the high heat flows, intense tectonism, and young surface ages in the SPT and small heat flows and greater surface ages inferred elsewhere over the satellite.
Han Liang
Showman Adam P.
Tobie Gabriel
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