Lurking in the Shadows: Wide-Separation Gas Giants as Tracers of Planet Formation

Abstract

Over the past two decades, thousands of planets with an extraordinary diversity of properties have been discovered orbiting nearby stars. Many of these exoplanetary systems challenge our narrative for how planets form and evolve, motivating the search for observational clues to the underlying mechanisms that led to this diversity. In this quest, gas giant analogs to our own Jupiter and Saturn immediately stand out as the most visible relics of the planet formation process. They are products of their birth environment, with properties such as atmospheric and interior compositions, masses, and formation locations sculpted by protoplanetary disk and host star properties. They also actively shape their surroundings; early in their lifetimes, gas giants can alter the structure of the gas disk from which additional planetary bodies may coalesce and affect the transport of rocky and icy materials to the inner disk. After the gas has dissipated these same behemoths can push smaller planets around, causing them to migrate or even ejecting them from the system. Thus to explain the observed diversity of exoplanet systems, we must first understand how gas giant planets form and evolve. This thesis presents four studies that harness multiple observational techniques to explore this question of how gas giant planets outside our solar system form and evolve.