Enabling the Discovery and Characterization of New Worlds Via Space-Based Direct Imaging

Abstract

The demographics and atmospheric properties of giant exoplanets reveal key insights into the formation and evolution of planetary systems. The occurrence rate of giant planets is known to correlate with both orbital semimajor axis and host star mass, however the exterior regions (beyond 10 au) around the lowest-mass stars (M dwarfs) have remained chronically under-investigated. In addition, giant planets form at high temperatures and cool gradually, which results in significant atmospheric changes over million-year timescales. Observations of giant planets at a range of planet ages are thus needed to constrain models of their atmospheric evolution. This thesis approaches such observational challenges with the direct imaging technique, which simultaneously provides sensitivity to wide-orbit giant planets and allows the direct characterization of atmospheric properties. First, I completed the data reduction and analysis of a JWST NIRCam survey of nine nearby, young M dwarf stars to search for planetary-mass companions (JWST GTO 1184, PI Schlieder). This study achieved unprecedented mass sensitivity for wide-orbit giant planets, and placed the first occurrence rate constraints on sub-Jupiter-mass exoplanets beyond 10 au around M dwarfs to be < 0.10 and < 0.16 objects per star with 1- and 3-sigma confidence respectively. Additionally, we identified a marginally significant exoplanet candidate near the target 2M J0944. Second, I led a follow-up observation campaign to attempt the confirmation of the planet candidate near 2M J0944 (JWST GO 3840, PI Bogat). We executed a similar observing strategy as in GTO 1184 with an increased exposure time, however this resulted in a non-detection and thus the dismissal of that source as a possible exoplanet. We did however redetect two extended sources which we show via astrometric and photometric analysis to be background galaxies, highlighting the unparalleled flux sensitivity of JWST NIRCam. Finally, I explored the feasibility of observing mature (age > 1 Gyr) giant planets in reflected, visible light with the soon-to-launch Roman Coronagraph. I performed modeling of confirmed planets discovered by the radial velocity technique, quantified the probability of successful detection with the Roman Coronagraph during the first 18 months of its primary mission, and identified the planet upsilon Andromedae d as the best target for the first reflected light observation of an exoplanet. This collection of work has leveraged emerging technology and observation strategies in space-based direct imaging to enable new demographics constraints and to open novel discovery space for benchmark giant exoplanets.