The Search for Exomoons and the Characterization of Exoplanet Atmospheres

Since planets were first discovered outside our own Solar System in 1992 (around a pulsar) and in 1995 (around a main sequence star), extrasolar planet studies have become one of the most dynamic research fields in astronomy. Our knowledge of extrasolar planets has grown exponentially, from our understanding of their formation and evolution to the development of different methods to detect them.
Now that more than 370 exoplanets have been discovered, focus has moved from finding planets to characterise these alien worlds. As well as detecting the atmospheres of these exoplanets, part of the characterisation process undoubtedly involves the search for extrasolar moons.
The structure of the thesis is as follows. In Chapter 1 an historical background is provided and some general aspects about ongoing situation in the research field of extrasolar planets are shown.
In Chapter 2, various detection techniques such as radial velocity, microlensing, astrometry, circumstellar disks, pulsar timing and magnetospheric emission are described. A special emphasis is given to the transit photometry technique and to the two already operational transit space missions, CoRoT and Kepler.
A review on the current situation of exoplanet characterization is presented in Chapter 3. We focus on the characterization of transiting planets orbiting very close to their parent star since for them we can already probe their atmospheric constituents. By contrast, the second part of the Chapter is dedicated to the search for extraterrestrial life, both within and beyond the Solar System. The characteristics of the Habitable Zone and the markers for the presence of life (biosignatures) are detailed.
In Chapter 4 we describe the primary transit observations of the hot Jupiter HD 209458b we obtained at 3.6, 4.5, 5.8 and 8.0 μm using the Infrared Array Camera on the Spitzer Space Telescope. We detail the procedures we adopted to correct for the systematic trends present in IRAC data. The lightcurves were fitted, taking into account limb darkening effects, using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques. We obtained the following depth measurements: at 3.6 μm, 1.469±0.013 % and 1.448±0.013 %; at 4.5 μm, 1.478±0.017 %; at 5.8 μm, 1.549±0.015 % and at 8.0 μm 1.535±0.011 %. Our results indicate the presence of water in the planetary atmosphere.
Chapter 5 is dedicated to the search for exomoons, we review some of the proposed detection techniques and introduce a model for the TTV and TDV signals which permits not only the identification of exomoons but also the derivation of some of their characteristics. We find that these techniques could easily detect Earth-mass exomoons with current instruments.
Finally, in Chapter 6 the detectability of a habitable-zone exomoon around various configurations of exoplanetary systems with the Kepler Mission or photometry of approximately equal quality is investigated. We calculate both the predicted transit timing signal amplitudes and the estimated uncertainty on such measurements in order to calculate the confidence in detecting such bodies across a broad spectrum of orbital arrangements. The effects of photon noise, stellar variability and instrument noise are all accounted for in the analysis. We validate our methodology by simulating synthetic lightcurves and we find that habitable-zone exomoons down to 0.2M⊕ may be detected and ∼ 25,000 stars could be surveyed for habitable-zone exomoons within Kepler ‘s field-of-view.