Identification and Characterization of an Exoplanet Candidate Using Multi-Mission Photometry and Spectroscopy.

: This thesis presents the discovery and analysis of Kepler-54 d, an exoplanet candidate identified through the integration of archival datasets from NASA's Kepler mission and the Transiting Exoplanet Survey Satellite (TESS). The study employs transit photometry to detect a periodic signal and uses Markov Chain Monte Carlo (MCMC) fitting techniques to estimate key planetary parameters. The candidate, with a radius of approximately 3.2 Earth radii and an orbital period of 8.01 days, falls into the mini-Neptune category and orbits a K7V-type star. Simulated atmospheric spectroscopy suggests the presence of water vapor and methane, although no biosignatures were found. The study emphasizes the usefulness of combining multiple space missions for exoplanet characterization and proposes follow-up observations with next-generation telescopes like the James Webb Space Telescope (JWST). This research contributes to the expanding understanding of planetary systems around low-mass stars. Keywords: Exoplanet, Kepler-54 d, Transit Photometry, Spectroscopy, TESS, Kepler, Exoplanet Characterization, JWST, Atmospheric Modeling, Habitability.