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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.

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1 C h a p t e r 1 FOREWORD ―Are there other worlds and other beings?‖ these profound questions have always been part of our history and culture. The greatest figures of Classical Civilisation, from Leucippus (5th century BC) to Epicurus (341 BC - 270 BC), and renowned philosophers, from Giordano Bruno (1548-1600) to Immanuel Kant (1724-1804), supposed we cannot be alone in the Universe. These eminent thinkers were following an ancient philosophical and theological tradition, but their ideas were not based on any experimental or observational evidence [1]. Proof of the existence of other worlds had to wait until Galileo turned his telescope to the night sky 400 years ago. Galileo was the first to truly see the planets and moons in our Solar System as other worlds. Yet it took until the end of the 20th Century before we developed telescopes and spacecraft to view –up close-the planets, their moons, and the persistent debris from which they have formed. All of these hold deep secrets of the Earth‘s origins and likely the beginning of life itself. It is ironic that what is arguably the most compelling subject in astronomy-the search for other worlds and other life beyond our Solar System-emerges only now, in the 21st Century. Four centuries of discovery have brought us a remarkable understanding of the birth and evolution of stars, the history of galaxies, and even cosmology-the development of the entire universe. Not for a lack of imagination or motivation, but simply for the want of technology, our oldest and deepest questions, the ones most relevant to our own origins and fate, have remained beyond our grasp for thousands of years. About fifty years ago, a great scientist and storyteller like Isaac Asimov estimated that about a billion Earth-like planets may exist just in our galaxy. Even reducing this number a hundred times, as suggested by less optimistic predictions, it remains extremely large. Nevertheless, in our galaxy there is a huge number of stars, around 200 billion, and probably a lot of them host a planetary system. It was only in 1988 that we

Laurea liv.II (specialistica)

Facoltà: Scienze Matematiche, Fisiche e Naturali

Autore: Giammarco Campanella Contatta »

Composta da 171 pagine.


Questa tesi ha raggiunto 122 click dal 03/09/2009.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.