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- Konatham, Samuel, 1992-
(författare)
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Atmospheric Species and Spectral Radiation in Terrestrial Exoplanets : Implications for Astrobiology
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The physical properties of the planets and their parent stars are fundamental in the composition of atmospheres and radiative environments, which fundamentally determine their surface temperature and habitability. The atmospheric composition and radiation play a vital role in the emergence of life. This doctoral thesis presents two main results: 1. A method that uses the physical properties of the planets and their parent stars to infer the potential atmospheric compositions of the known exoplanets. For that, fundamental physics concepts and the basics of the kinetic theory of gases are used. Additionally, a new list of potentially habitable exoplanets is presented based on the resulting atmospheric compositions and the criteria that Earth-like atmospheres that can host liquid water should be considered habitable. The presented method also provides a preliminary classification of exoplanets similar to Earth (in terms of atmosphere) and their potential habitability. 2. A study of the impact of the radiation environment on the development and evolution of the human visual system towards optimal use of the available radiation. Human vision's possible evolutionary directions are presented while overcoming the shortcomings in the existing studies. The human visual system is hypothesised to have evolved in conjugation with the prevailing spectral radiation environment for photopic (daytime) and scotopic (night-time). One of the main novelties of this study is the comparison of the human vision bandwidth with the Full Width at half-maximum (FWHM) of the radiation reaching the shallow depths of the ocean, which may suggest that this is optimized for the development of animal sight during the formation of the early proto-visual system. Moreover, the observed maximum absorption wavelength during photopic vision (555nm) correlates with the maximum total energy for a 300 nm vision bandwidth. Furthermore, the analysis of the radiation environment at different solar zenith angles (SZA) during dusk suggests that the scotopic vision evolved to optimize information retrieval during these hours. The work presented in this thesis contributes to perform screening of Earth-like exoplanets and the study of astrobiological or space exploration aspects such as potential habitability, human-like vision, photosynthesis efficiency and evolution of life systems on exoplanets.
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| 2. |
- Vakkada Ramachandran, Abhilash
(författare)
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A planetary chamber to investigate the thermal and water cycle on Mars
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The water processes that affect the upper layers of the surface of Mars are not yet fully understood. Describing the processes that may induce changes in the water content ofthe surface is critical to determine the present-day habitability of the Martian surface,understand the atmospheric water cycle, and estimate the efficiency of future water extraction procedures from the regolith for In-Situ-Resource-Utilization (ISRU). This PhD thesis describes the design, development, and plausible uses of a Martian environmental facility ‘SpaceQ chamber’ which allows to simulate the near surface water cycle.This facility has been specifically designed to investigate the effect of water on the Martian surface. SpaceQ has been used to investigate the material curation and has demonstrated that the regolith, when mixed with super absorbent polymer (SAP), water, and binders exposed to Martian conditions, can form a solid block, and retain more than 80% of the added water, which may be of interest to screen radiation while maintaining a low weight. The thesis also includes the testing of HABIT operation, of theESA/IKI ExoMars 2022 robotic mission to Mars, within the SpaceQ chamber, underMartian conditions similar to those expected at Oxia Planum. The tests monitor the performance of the brine compartment, when deliquescent salts are exposed to atmospheric water.In this thesis, a computational model of the SpaceQ using COMSOL Multiphysics has been implemented to study the thermal gradients and the near surface water cycle under Martian temperature and pressure experimental conditions. The model shows good agreement with experiments on the thermal equilibration time scales and gradients. The model is used to extrapolate the one-point relative humidity measurement of the experimental to each grid points in the simulation. This gives an understanding ofthe gradient in atmospheric water relative humidity to which the experimental samples such as deliquescent salts and Martian regolith simulants are exposed at different time intervals. The comparison of the thermal simulation and the experimental behavior of HABIT instrument tests, shows an extra internal heating source of about 1 W which can be attributed to the hydration and deliquescence of the salts exposed to Martian conditions when in contact with atmospheric moisture.Finally, this thesis experimentally demonstrates that pure liquid water can persist for 3.5 to 4.5 hours at Mars surface conditions. The simulated ground captured 53% of the atmospheric water either as pure liquid water, hydrate, or brine. The result concludes that the relative humidity values at night-time on Mars may allow for significant water absorption by the ground, which is released at sunrise. The water cycle dynamics near the surface is therefore always out of equilibrium. After frost formation, thin films of water may survive for a few hours. The results of this thesis about the water cycle on Mars, and about the interaction of atmospheric water with regolith and salts, have implications for the present-day habitability of the Martian surface and planetary protection policies.
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