HR: 0800h
AN: T41C-1321    [Abstracts]
TI: ``One is the Loneliest Number That You'll Ever Do...Thermal Evolution Calculations are Better in Two (or 3D)
AU: * Redmond, H L
EM: redmondh@purdue.edu
AF: Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907 United States
AU: King, S D
EM: sking@purdue.edu
AF: Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907 United States
AB: The thermal histories of the terrestrial planets have been previously calculated using 1D parameterized convection simulations. While these calculations are qualitatively useful, several key assumptions and estimations must be made to bring the calculation to a 1D energy balance using the following relationship between the Rayleigh number (Ra) and Nusselt number (Nu), Nu = Ra^β The value of the exponent β varies considerably depending on model assumptions. Further, as a planet cools, it passes through stages where different values of the exponent would be appropriate. Because the full equations of convective motion can be solved in a few hours (2D) to several days (3D) with numerical simulations in Cartesian or spherical geometry, comparing 1D and full 2D calculations is fitting. We have illustrated that full 2D convection calculations of the thermal history of Mercury are similar to previous 1D calculations early on, but produce different results in later stages of evolution. Prior results suggest that mantle convection on Mercury can not persist up to present, implying no present-day core dynamo or a nearly extinct dynamo. However, a recent study argues that a core dynamo could, and is likely to, exist at present. Thus, if a sufficient core heat flux exists at present due to outer core convection, we contend it would likely support current mantle convection. Our simulations, which use a dry, non-Newtonian rheology, moderately-sized Rayleigh numbers and core heat fluxes that are constant through time, indicate that sluggish convection can survive at present, producing small but discernible dynamic topography or hermeoid anomalies. Thus, 1D thermal history calculations oversimplify the full equations of convective motion. We explore the thermal histories of a Venus/Earth-sized body and a Mars-sized body using the same 2D Cartesian convection formulations we used for Mercury. We present a series of thermal evolution simulations in an olivine rheology that are run for 4.5 billion years and vary the Rayleigh number, core heat flux, and mantle internal heating rate. We then compare our results to previous 1D thermal history models. With a non-Newtonian rheology in a Mars-sized body, we observe a sharp transition in the onset of convection. This illustrates that convection may be strongly rheology-dependent. Further work includes studying the effect of a Newtonian rheology and rate of mantle internal heating on convection in a Mars- and Earth/Venus-sized body.
DE: 0500 COMPUTATIONAL GEOPHYSICS (3200, 3252, 7833)
DE: 0545 Modeling (4255)
DE: 5430 Interiors (8147)
DE: 8125 Evolution of the Earth (0325)
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Tectonophysics [T]
MN: Fall Meeting 2005