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Anelastic deformation of planetary bodies
Vach, Dominik ; Čadek, Ondřej (advisor) ; Běhounková, Marie (referee)
Observations indicate an existence of subsurface oceans for some of the icy moons in the Solar System which are heated by the tidal forces. In order to describe this anelastic deformation, the methods well-known from the continuum mechanics were employed, and thus the dissipation was calculated for various bodies. In the thesis, Maxwell and Kelvin-Voigt model were compared in their ability to predict the heating power of the bodies. In contrast to the Maxwell model, the Kelvin-Voigt model, which is generally not used in geophysics, repre- sents reversible processes, and thus could explain the effects which are otherwise explained only by the gravity. A program in Fortran was developed in order to compare the models by modelling 3D anelastic deformation of planetary bodies under the effect of tidal forces. The results indicate the predicted power can be various for both models and Kelvin-Voigt model could be used e.g. to describe short run deformation processes. 1
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Evolution of terrestrial exoplanets
Káňová, Michaela ; Běhounková, Marie (advisor) ; Čadek, Ondřej (referee)
Observations of terrestrial exoplanets provide a unique statistical set that may improve our knowl- edge of their formation, structure as well as internal and orbital evolution. Close-in extrasolar planets are subjected to strong stellar tides, resulting in an extensive dissipation of mechanical energy (tidal heating), long-term orbital evolution and evolution of the rotational frequency. For the exoplanets on eccentric orbits, the traditional tidal theories predict locking into pseudo-synchronous spin states, for which the rotational frequency is slightly higher than the orbital frequency. Such predictions are, how- ever, in contradiction with the observations of moons in the Solar system, and are a consequence of simplified rheological assumptions. Here, we focus on a numerical approach to the tidal evolution of planetary orbit and rotation in a single-planet system, assuming a Maxwell viscoelastic rheology. We find equillibrium spin states, including the spin-orbit resonances, and discuss their connection with the minima of tidal heating. Locking into a spin-orbit resonance results in an irregular insolation pattern and an unequal surface temperature distribution, affecting the internal dynamics of the planet. The second part of the thesis therefore deals with the evaluation of the surface temperature and...
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Termální vývoj Saturnova měsíce Enceladu
Kozoň, Marek ; Čadek, Ondřej (advisor) ; Běhounková, Marie (referee)
We study thermal evolution of Enceladus on very long time scales. In order to do so, we created a Fortran program modeling tidal deformation and thus induced heat dissipation as well as conductive transport of the heat in the body of the moon. Effect of long-lived radioactive isotopes decay in the core on the heat generation is included. We show the dependence of a thermal scenario character on different minimal viscosity and constant eccentricity values and study chosen cases in detail. We further demonstrate that, if orbital eccentricity evolution is incorporated, its initial value has no essential effect on the thermal evolution result, with the body always freezing quickly. Lastly, we examine the dependence of a thermal scenario on added values of hydrothermal heating power from the core and present that a power magnitude can be found, with which the satellite does not freeze, nor overheats in the first 4 billions of years what is necessary for maintaining a thermal activity on Enceladus since its formation to the present time. 1
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Insolation pattern and surface temperature on extrasolar planets
Káňová, Michaela ; Běhounková, Marie (advisor) ; Čadek, Ondřej (referee)
We study evolution and distribution of surface and near-surface temperature on tidally locked extrasolar terrestrial planets without atmosphere. In order to determine the temperature, insolation patterns depending on eccentricity, obliquity and spin-orbit resonance are computed and thermal diffusion equation is solved in a spherical shell. We discuss the dependence of temperature distribution on physical and geometrical parameters including orbit eccentricity, obliquity of rotational axis, type of spin-orbital resonance, thermal inertia and irradiance incident on the planetary surface (the extra- solar constant). The mean annual temperature is driven especially by the extrasolar constant and may rise up to thousand of kelvins in the most irradiated regions. Effect of eccentricity, obliquity and thermal inertia, in some cases, is on the scale of hundreds of kelvins.
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Regional models of lithospheric subduction
Androvičová, Adela ; Čížková, Hana (advisor) ; Běhounková, Marie (referee)
Processes within subduction zones have major influence on the plate dynamics and mantle convection. Subduction process is influenced by a combination of many parameters and there is no simple global relationship between the resulting slab geometry and deformation and any specic subduction parameter. In the present work we perform a parametric study of the slab dynamics in a two-dimensional model with composite rheology including diffusion creep, dislocation creep and stress limiting rheology or Peierls creep. In our model, the separation of the subducting and overriding plates is ensured by a layer of a low viscosity material. We are particularly interested in the effect of the contact of subducting and overriding plate on the plate geometry in the upper mantle. We also study the influence of a surface boundary condition and the rheologic parameters of the plate. Model results are applied to the Kermadec subduction zone. We show that the model that best fits the observed morphology and plate velocities is the model with viscosity of crust of 1020 Pa.s, yield stress of 108 Pa and with a viscosity jump by a factor of 10 at the depth of 660 km.
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Internal dynamics of Mars: a study based on gravitational and topographic data
Kalousová, Klára ; Běhounková, Marie (referee) ; Čadek, Ondřej (advisor)
In the present work we deal with the model of elastic lithosphere thickness on Mars. We assume that the surface load of the planet is compensated only by elastic lithosphere deflection and formulate the spatial inversion based on the comparison between predicted and observed geoid. Performing very extensive tests on this inversion in the two dimensional axisymmetric geometry we gain its best parameters. Then we invert the real data and construct the models of Martian elastic lithosphere thickness for filters of variable width. We focus on some topographically significant areas, establish the elastic lithosphere thickness below them and compare the obtained values with published results. For some areas we get agreement. Assigning the age to particular areas we find the growth of elastic lithosphere thickness during time, which is in agreement with the so-called principle of frozen lithosphere.
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