It’s Not Just a Phase

The amount of light an exoplanet reflects and emits towards an observer waxes and wanes as the planet orbits through its phases. The amplitude and profile of reflection phase curves constrain the albedo of planetary surfaces and atmospheres, while the thermal amplitude and profile reveal temperature distributions and heat transport efficiencies, all providing valuable insight into the nature of exoplanet surfaces and atmospheres. In this dissertation I highlight the usefulness of utilizing full orbital phase curves in addition to occultation measurements, which provides a higher sensitivity to planetary photons at the expense of a more challenging data reduction. In the first few chapters of this dissertation, I introduce a novel non-parametric algorithm to produce clean, robust exoplanet phase curves, and apply it to separate ensembles of 115 Neptunian and 50 Terran exoplanets observed by the Kepler satellite to measure an upper limit on the average albedo of Kepler’s Neptunian planets, and make the first constraint on the average albedo of Terran worlds. In the fourth chapter, I present the full orbital phase curve and occultation of the ultra-hot Jupiter WASP-100b observed by the Transiting Exoplanet Survey Satellite (TESS), and with the use of Bayesian methods, present the first measurement of a phase shift of the thermal maximum among the phase curves observed by TESS, the degree of which challenges the predicted efficiency of heat transport in the atmospheres of ultra-hot Jupiters. In the final chapter, I present an example of how the NASA ROCKE-3D general circulation model can be used to explore the physical mechanisms that influence the habitability of terrestrial exoplanets, and then show how I generated phase curves from the 3-dimensional models to study the signals produced by simulated TRAPPIST-1 habitable-zone worlds. The work in this dissertation contributes valuable new information to the astronomical literature and provides avenues for further research on the nature of short-period exoplanets.