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Author
Date
2023Type
- Doctoral Thesis
ETH Bibliography
yes
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Abstract
The field of exoplanet research is a young and vibrant area of study, continually evolving and expanding as new discoveries and technologies emerge. More than 5500 exoplanets in over 4000 planetary systems have been found in the last two decades by various detection techniques. While many of these detected worlds are unsuitable for supporting life, there is a growing number of potentially habitable terrestrial planets being discovered. For the first time in human history, advancements in technology and science now place us on the verge of being able to search for signs of life beyond our solar system. This requires the direct detection of their atmospheres, which provide invaluable insights into planetary habitability and the potential discovery of extraterrestrial life. One key challenge, however, is the correct interpretation of their spectra. Measured exoplanet spectra are global averages (due to the large exoplanet-observer separation). Hence, local variations in the atmospheric composition, pressure-temperature (P-T) structure, and clouds are unresolved. Additionally, due to the faint nature of their signals, the temporal and spectral resolution is limited. Thus, observations of terrestrial habitable zone exoplanets are spatially and temporally averaged, low-resolution spectra. To prepare for future attempts to characterize these distant habitable worlds, studying Earth and its characteristics from afar offers a unique opportunity to explore a truly habitable and inhabited world. In this thesis, I follow a data driven approach to investigate Earth’s thermal emission spectrum and its time-variability in the context of exoplanet research. By leveraging the wealth of Earth observation data, I investigate Earth’s time-resolved and spectrally-limited thermal emission spectrum for five specific target locations in Chapter 2. Then I expand the analyses from time-resolved to spatially- and time-unresolved mid-infrared (MIR) spectra for different full-disk observing geometries in Chapter 3. In Chapter 4, I use these disk-integrated MIR spectra as input for atmospheric retrievals and, for the first time, perform a systematic retrieval analysis of real disk- and time-averaged Earth spectra, where the retrieval results can be compared to ground truths from Earth observation. My research yielded two comprehensive datasets with matching ground truths. Using these datasets, I demonstrated that a representative, disk-integrated thermal emission spectrum of Earth does not exist. Instead, both the thermal emission spectrum and the strength of spectral absorption features show seasonal variability and depend on viewing geometry. In addition, a strong spectral degeneracy with respect to viewing geometry and season was found. This indicates that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Finally, investigating Earth as a directly imaged exoplanet by means of the future MIR space mission concept LIFE, showed that that the mission would correctly identify Earth as a planet where life could thrive, with detectable levels of bioindicators, a temperate climate, and surface conditions that allow for liquid surface water. In conclusion, the analyses and results presented in this thesis, demonstrate the power of thermal emission data for the characterization of habitable terrestrial exoplanets, but they also caution us to be careful in the analysis and interpretation. The interdisciplinary approach of exoplanetary science, planetary science, and remote sensing of solar system bodies offers a promising framework to pave the way for the detection of life beyond our solar system. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000652081Publication status
publishedExternal links
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Publisher
ETH ZurichSubject
Earth and Planetary Astrophysics (astro-ph.EP); Remote sensing; exoplanetsTerrestrial planetsAtmospheric modelingSpectroscopyMissions; ExoplanetsOrganisational unit
09680 - Quanz, Sascha Patrick / Quanz, Sascha Patrick
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ETH Bibliography
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