Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astronomy

First Advisor

Laughlin, Gregory

Abstract

The study of exoplanetary systems offers an observable window into the processes governing celestial bodies' formation, evolution, and current structure. Central to understanding these systems is their geometry, which encompasses the orientations, alignments, and spatial relationships among planets and their host stars. This dissertation investigates the pivotal role of planetary system geometry - particularly obliquities and orbital resonances - in illuminating the formation pathways and long-term evolutionary trends of both solar and exoplanetary systems. This dissertation explores these themes through three comprehensive studies. Chapter \ref{ch:TidalQ} focuses on the role of tidal dissipation in shaping short-period exoplanets, examining whether the presence of obliquity-driven tidal interactions can distinguish between different planetary populations. This study highlights how dissipation processes influence orbital stability and potential differences in composition between rocky super-Earths and gaseous sub-Neptunes. Understanding the role of tidal quality factors in these systems provides a lens into the evolution of planets near orbital resonances, bridging observations with theories of internal structure and formation. Chapter \ref{ch:Keck} focuses on stellar obliquities and their implications for system alignment. Using data from TESS and Kepler, we show that stellar temperature plays a significant role in determining obliquity, with hotter stars exhibiting higher misalignment than cooler stars. This finding connects the geometric properties of exoplanetary systems to stellar physics and evolutionary dynamics, revealing the complex relationship between stellar structure, rotational dynamics, and the alignment of planetary orbits. This work advances our understanding of how star-planet interactions contribute to system architecture by situating these findings within the broader context of stellar obliquity studies. Finally, Chapter \ref{ch:polar} delves into the mysterious class of polar Neptunes, exploring their formation through the lens of disk-driven resonance and their subsequent evolution over Gyr timescales. I demonstrate that while true polar Neptune orbits are stable and resist realignment, systems with moderate obliquities can undergo significant tidal interactions that alter their orbits over time. Case studies of systems such as HAT-P-11 and WASP-107 provide empirical support for these theories, constraining the tidal quality factors and reinforcing the plausibility of disk-driven resonance as a formative mechanism. This research integrates observations, long-term simulations, and theoretical predictions to show how orbital tilts and interactions influence system stability and composition. The overarching goal of this dissertation is to connect the geometric properties of exoplanetary systems with theories of evolution and formation. By analyzing how obliquities link to origins, resonances to compositions, and evolutionary processes to the conditions of formation, this work seeks to contribute to a unified framework for planetary system formation. Ultimately, this dissertation underscores the critical role of geometric properties as both a diagnostic tool and a window into the origins and evolution of planetary systems, advancing our understanding of the cosmic processes that shape them.

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