The Atmospheres of the Hottest Exoplanets at High Spectral Resolution

What would happen to Jupiter if we moved it two hundred times closer to the Sun? While we cannot conduct such experiment, exoplanets, or planets around other stars, allow us to explore a range of conditions unthinkable to achieve in the Solar System. The first exoplanets were only found three decades ago, but today we know of over 5000 of them, including some rather bizarre “ultrahot Jupiters”: gas giants orbiting so close to their stars that most of their molecules are ripped apart by the extreme heat. In this thesis, we take a tour through our stellar neighborhood to study the atmospheres of some of these exotic worlds and understand their compositions and climates. Our tool in this journey is high resolution spectroscopy, a technique that splits the light from an exoplanet into a myriad of colors to search for the unique fingerprints of the different atmospheric constituents. We start by exploring HAT-P-70b, one of the hottest exoplanets in the Northern Sky. Our analysis of this oddball reveals a remarkably rich atmosphere, full of vaporized metals like calcium, chromium, and iron, blowing around the planets with velocities of several kilometers per second. Our journey also takes us to the puffiest known exoplanet, HAT-P-67b. Here, we find an atmosphere potentially eroding away due to the high stellar irradiation. Our work also demonstrates that high resolution spectroscopy is not exclusive to large ground-based telescopes, and that modest facilities, like the Nordic Optical Telescope, can join the efforts to study the atmospheres of other exoplanets. Eventually, with the next generation of extremely large telescopes, the tools currently developed to study ultrahot Jupiters will be applied to potentially habitable Earth-like planets in an attempt to find out if life has developed on other worlds.