Plastic Yielding and Tectonic Regimes in Thin Ice Shells: Effects of Latitudinal Surface Temperature Variations
Abstract
The satellites of the outer solar system show varying levels of geologic activity, ranging from the relative quiescence of Callisto to the more dynamic surfaces of Miranda, Enceladus, and Europa. Unraveling how heat is transferred through the outer ice shells is important for understanding the evolution of icy bodies. Here, we explore variable surface temperatures and rheology as the controlling parameters for possible convective shell states using 3-D numerical experiments of global visco-plastic thin shell convection. An important aspect of ice shell convection may be that of latitudinally variable surface temperature (Ts), which arises from differing angles of insolation. For the icy satellites, this latitudinal variance in surface temperature may reach a significant fraction of the melting temperature of water ice. The net effect is to favor a global degree-2 "Hadley cell" type flow pattern, with upwellings focused near the equator and downwellings near the poles. As Solar luminosity increases (proximity to or age of the Sun), this effect becomes more pronounced. We also characterize tectonic regimes as functions of Rayleigh number (buoyancy forcing), temperature dependence of viscosity, and plastic yield stress. Surface deformation patterns are yield stress dependent, with short wavelength deformation favored by lower yield stresses, and degree-1 structures favored for higher yield stresses. Variable Ts acts to orient flow and deformation poleward, and amplifies surface stresses. Ice shells operating under these higher stress regimes can yield at higher values than constant surface temperature cases would predict. These results may help explain observations of surface features in the outer satellites, such as Europa's enigmatic "crop circles". More generally, understanding the long-term evolution of the thermal state of icy bodies is of relevance for questions including the existence of potential subsurface oceans and any possibility for life.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P52B..03W
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6221 Europa;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6282 Enceladus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS