On the atmospheres of Saturn and cold gas giant extrasolar planets
Dalba, Paul Anthony
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Over the past few decades, short-period giant planets have been discovered in extrasolar planetary systems, allowing for new tests of planetary evolution theories. Many of these giant exoplanets have high temperatures (>1000 K) and do not directly resemble Jupiter or Saturn. Only in the past few years have exoplanets akin to the cold (~100 K) gas giants in the solar system been identified. In this dissertation, I investigated giant gaseous planets through comparative studies of Saturn and exoplanets. Saturn has been the target of numerous high-precision observations, making it the ideal candidate for comparative studies. I simulated transit observations of a Saturn-analog exoplanet and determined that cold exoplanet atmospheres are amenable to characterization via transmission spectroscopy. By casting Saturn as an exoplanet, I demonstrated the potential for exoplanets to place the solar system in a Galactic context. The transit spectrum of Saturn also highlighted the importance of atmospheric refraction in transit observations. Refraction alters the path of light propagating in an atmosphere. I showed that out-of-transit refracted light provides an opportunity to identify and characterize the atmospheres of cold transiting and non-transiting exoplanets. I searched exoplanet parameter space to locate the maximal effect and derived a criterion that predicts which atmospheres produce detectable refracted light signatures. My consideration of exoplanetary refraction also included a parallel study of Saturn's atmosphere. I developed a novel method to measure atmospheric refractivity from distorted images of the Sun. I used this method to infer Saturn's atmospheric structure for more than a dozen Saturn solar occultations and to identify seasonal variations in Saturn's stratospheric temperature. Lastly, I obtained ground-based observations of the long-period transiting exoplanet Kepler-421b to refine its transit ephemeris. Without accurate transit ephemerides, long-period exoplanet characterization with large space-based observatories cannot occur. My unique observations represent the first step toward ensuring that long-period exoplanets are characterized in the near future. In summary, this dissertation lays the foundation for investigations of cold giant exoplanets, which exist in an almost entirely unexplored regime of exoplanetary science. Using Saturn to provide context and motivation, I began confronting the challenges facing this new discipline of exoplanetary science.