The composition and dynamics of exoplanet atmospheres.

Abstract

The study of exoplanets has rapidly developed in the last twenty years, and the detailed characterization of planetary atmospheres has become a key area of research. For transiting planets around bright stars, atmospheric features can be detected with transmission spectroscopy. I will present a low resolution transmission spectrum of WASP-52b, and show that the most likely interpretation is that the planet is shrouded with an opaque cloud layer. By using transmission spectroscopy at much higher resolution, in this thesis I will present the first spatially resolved measurements of a weather system in an exoplanet. By modeling the absorption profile of sodium on HD189733b, I show that the planet atmosphere has an excess velocity not explained by planetary rotation. HD209458b is evaporating under intense irradiation from its star, and may lose as much as 1010 g s-1. Mechanisms of mass loss are poorly understood, in particular the efficiency. To calculate this rate for HD209458b a key component is missing - the high energy flux of the star. I will demonstrate that it is possible to recover this flux by building a coronal model for the star, using constraints for different temperatures of plasma from UV and X-ray sources. I will present commissioning data gathered with NGTS that are the most precise ever gathered with a ground based wide field transit survey. Simulations of the performance of NGTS in this thesis show that the survey can be expected to detect ~200 low mass planets. The simulations of NGTS also show that a sample of bright super-Earths and hot-Neptunes can be expected to be detected, which would be sensitive to the same techniques performed on hot Jupiters in this thesis. One day, these same techniques could be important tools for characterizing the atmospheres of Earth analogs