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| Titel |
Realistic thermal evolution models for Superearth Exo-solar planets |
| VerfasserIn |
A. van den Berg, D. Yuen, K. Umemoto, R. Wentzcovitch, M. Jacobs |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061463
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| Zusammenfassung |
| Massive superearth exoplanets in the range of one to ten times the Earth's
mass have a much extended pressure regime compared to Earth,
up to about 1 TPa, that may give rise to different material behavior.
This has an impact on planetary evolution, and the evolution of a magnetic field
and planetary atmosphere, and is therefore also relevant for habitability conditions.
The material properties concerned include the mantle rheology where pressure affects both
deep mantle viscosity and the brittle-ductile transition,
both with a direct impact on lithosphere dynamics and the heat transport
capacity of superearth mantle convection.
Besides rheological considirations, other material properties also show strong
variation with both pressure and temperature,
in particular thermal expansivity and thermal conductivity.
At ultra-high pressure they will exert a strong impact on the
effectiveness of convective heat transport.
The commonly used (extended) Boussinesq (EBA) convection model is not
well suited for the pressure regime of superearth exoplanets
becuase of the high value of the surface dissipation number involved, typically
Di ~ 5 (van den Berg et al., Phys. Earth Planet. Inter.,178, 136-154).
We therefore use a compressible convection model based on the anelastic liquid
approximation and apply a selfconsistent model for the thermophysical
properties based on ab-initio and lattice dynamics for relevant mantle
silicates, perovskite, post-perovskite and periclase
(Umemoto et al., Science,311, 983-986, 2006;
Jacobs and van den Berg, Phys., Earth Planet. Inter.,186, 36-48, 2011).
In particular our model includes, in a selfconsistent way, the significant
temperature dependence of thermal expansivity, important in controlling
the dynamics of cold downwellings in the upper mantle.
We present results of convection modelling experiments exploring the
forementioned model sensitivities on mantle heat transport
both in transient cooling models and expressed in terms of Nusselt-Rayleigh number
relationships.
We show that deep mantle rheology parameterized through an activation
volume of the dominant creep mechanism as well as a pseudo-brittle lid
controlling stagnant behavior are important factors determining the
thermal state. |
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