Characterization of the atmospheres of extrasolar planets with Ariel

Extrasolar planet (exoplanet) science has rapidly expanded over the past decades, with thousands of exoplanets discovered using techniques such as the transit method. As the field progressed, the focus shifted from measuring fundamental planetary parameters to understanding the nature of these faraway worlds. The James Webb Space Telescope is a monumental step in this direction. However, studying select targets needs complementing with unbiased surveys of the diverse exoplanets we can currently observe. This will be a legacy of the Ariel space mission, which will perform the first spectroscopic survey of the atmospheres of exoplanets, enabling comparative planetology studies on a Galactic scale. This thesis presents my work over three years of Ph.D. research to prepare exoplanet atmospheric characterization with Ariel. Preparing the Ariel mission requires extensive studies, from optimizing the mission design and observation strategy to developing representative simulators and data analysis tools. At a high level, this thesis is a three-stage progression: it begins by framing the scientific context and motivation for Ariel, then evaluates the expected performance of the mission, and finally develops tools to reduce and analyze simulated Ariel data. Characterizing the atmospheres of exoplanets with Ariel requires the combined expertise and dedication of numerous scientists, engineers, and institutions. While advanced instrumentation enables the mission, it is the people involved who drive its success. Ariel is more than flying hardware: it is a culmination of human ingenuity, teamwork, and vision. My work fits into this broader effort of individuals collaborating to maximize Ariel's scientific potential and ensure its legacy, on the path of understanding these alien worlds.