Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p42b..10r&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P42B-10
Other
[5475] Planetary Sciences: Solid Surface Planets / Tectonics
Scientific paper
The large temperature excess in young planets is probably evacuated as much by intense volcanic activity as by thermal diffusion across a lithosphere. However, most fluid dynamic codes in Earth Science are implementing a zero vertical velocity at the surface of their models. This condition forbids any direct transport of material and therefore any direct extraction of heat from depth. We propose a new set of boundary conditions on the top surface for the momentum and energy equations. The vertical velocity is not imposed to zero but we compute the topography generated from this velocity. A diffusion term mimics the various processes that can redistribute the topography (mechanical and chemical erosion, gravity sliding, magma spreading on the surface...). The resulting topography affects the internal flow by imposing an equivalent vertical stress to the mantle. We show that with minimal approximations the new condition can be very easily implemented. In the energy equation we only impose a surface temperature when the surface velocity is downward and a zero temperature gradient elsewhere. Our 2D numerical simulations of bottom heated convection show that when increasing the Rayleigh number, the model evolves continuously from the typical pattern of convection and heat diffusion through a thermal lithosphere to a planform where all the heat is brought to the surface by large plumes. The extracted heat flux increases with the Rayleigh number from Ra^.3 at low Rayleigh number to Ra^.5 at high Rayleigh number where simultaneously, the planet temperature decreases from .5 to very low values. We discuss the implication of this model for the early evolution of the Earth and other solid planets, and the present state of Io.
Dubuffet Fabien
Labrosse S. J.
Ricard Y. R.
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