Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p24c..03v&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P24C-03
Physics
[5430] Planetary Sciences: Solid Surface Planets / Interiors, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [5475] Planetary Sciences: Solid Surface Planets / Tectonics, [6296] Planetary Sciences: Solar System Objects / Extra-Solar Planets
Scientific paper
Magnetic fields on terrestrial exoplanets can provide valuable constraints on the internal structure and dynamics of these planets, protect planetary atmospheres against stellar wind erosion, and shield planetary surfaces from charged particles. Many recently discovered exoplanets are on close-in orbits and this promotes tidal locking and must cause elevations in surface temperature of 100's to 1000's of K or, without atmospheric heat redistribution, strong (100's to 1000's of K) temperature contrasts between permanent day and night sides. To investigate potential internal magnetic field generation on these hot exo-Earths, we calculated core mantle-boundary (CMB) heat fluxes from numerical simulations of sub-solidus planetary mantle convection and use analytic scaling laws to predict magnetic field evolutions from CMB heat fluxes. We imposed either elevated surface temperatures or strong surface temperature contrasts in our mantle models, and employed a composite viscous/pseudo-plastic rheology to allow for plate tectonic behavior, for comparison to model planets with stagnant lid convection. Our preliminary results suggest that the average CMB heat flux is relatively insensitive to surface temperature elevations and hemispheric contrasts. This is due to similar trends in boundary layer thickness and temperature contrast at the CMB that tend to stabilize CMB heat flow. Thus, hotter mantles feature a smaller temperature contrast with the core, but also a relatively thin thermal boundary layer due to enhanced convective vigor in the lower viscosity mantle. Lateral variations in predicted CMB heat flux are typically ~50% of the average heat flux, and surface temperature contrasts of ~800 K induce only a minor hemispheric asymmetry in CMB heat flux of ~5%. Although such heat flux variations may disrupt a purely axial dipole field, the predicted boundary heterogeneity is well within proposed limits for the development of a stable internal dynamo. Surprisingly, CMB heat flow is only weakly sensitive to whether plate tectonics or stagnant lid convection operates, and our results demonstrate that magnetic field generation is feasible for stagnant lid planets with sufficient core-mantle heat transport.
Conrad Clinton P.
Gaidos Eric
van Summeren J.
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