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| Titel |
On the Problem of Deriving Scaling Laws for Plate-Tectonics on Terrestrial-Like Exoplanets |
| VerfasserIn |
L. Noack, D. Breuer |
| 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 |
250067099
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| Zusammenfassung |
| Space missions like Kepler and CoRoT led to a fast growing number of detected rocky
exoplanets up to 10 Earth masses, and a large effort is done in simulating the interior
processes of these planets including the atmosphere, surface processes, mantle convection
and core dynamos. These investigations help to find specific constraints on the habitability of
these planets (e.g. the likeliness of plate tectonics or the amount of outgassed volatiles)
and select candidates for future space missions which can observe only a limited
amount of planetary candidates (EChO for example can only observe 100 exoplanets
[0]).
Studies that try to investigate the likeliness of plate tectonics on exoplanets typically
extrapolate their results obtained for convection simulations of smaller planets or of planets
with a stiffer mantle (using higher reference viscosities) to obtain a general conclusion about
how larger planets would evolve with time. Further, parameterized model are often used to
investigate large parameter spaces. However, these models are based on scaling laws, which
are typically derived for small Rayleigh numbers and predefined viscosity contrasts (typically
105 to guarantee a stagnant lid), and hence may fail to yield realistic results if applied to
exoplanets.
In this study, we therefore concentrate on the dependence of the scaling laws on the
large-Rayleigh-number regime and the viscosity contrast (influenced either by a change in
surface temperature, activation energy or viscosity approximation). First results
of our parameter study show already that the scaling of convective stress below
the lid, root-mean-square velocity and Nusselt number leads to different scaling
parameters depending on the viscosity contrast, which has important consequences for
plate-tectonics simulations performed by parameterized models. A formulation
following
N u = θαRa β
for varying viscosity contrasts (with θ = ln(ηsurf-ηCMB)) and Rayleigh numbers but fixed
exponents α,β does not hold. The exponent of the Rayleigh number itself depends on the
viscosity contrast (β(θ)). We determine a universal scaling that fits to all viscosity contrasts
investigated.
We further compare the scaling exponent for different geometries (sphere vs. box [1])
and different ratios of core radius to planet radius. Finally, the scaling laws for the
convective stress are compared to plate tectonics simulations, where a specific factor (i.e.
surface temperature or mantle thickness) is varied, to verify of our new scaling
laws.
References
[0] EChO Science Requirements Document (2011). SRE-PA/2011.037, ESA.
[1] L. Noack and N. Tosi, submitted to Integrated Information and Computing Systems for
Natural, Spatial, and Social Sciences, in review. |
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