This book provides a detailed, state-of-the-art overview of key observational and theoretical aspects of the rapidly developing and highly interdisciplinary field of exoplanet science, as viewed through the lenses of eight world-class experts. It equips readers with a broad understanding of the complex processes driving the formation and the physical and dynamical evolution of planetary systems. It juxtaposes theoretical modeling with the host of techniques that are unveiling the exceptional variety of observed properties of close-in and wide-separation extrasolar planets. By effectively linking ingenious interpretative analyses to the main factors shaping planetary populations, the book ultimately provides the most coherent picture to date of the demographics of exoplanetary systems. It is an essential reference for Ph.D. students and early-stage career researchers, while the scope and depth of its source material also provide excellent cues for graduate-level courses.

The past decade has delivered remarkable discoveries in the study of exoplanets. Hand-in-hand with these advances, a theoretical understanding of the myriad of processes that dictate the formation and evolution of planets has matured, spurred on by the avalanche of unexpected discoveries. Appreciation of the factors that make a planet hospitable to life has grown in sophistication, as has understanding of the context for biosignatures, the remotely detectable aspects of a planet's atmosphere or surface that reveal the presence of life. Exoplanet Science Strategy highlights strategic priorities for large, coordinated efforts that will support the scientific goals of the broad exoplanet science community. This report outlines a strategic plan that will answer lingering questions through a combination of large, ambitious community-supported efforts and support for diverse, creative, community-driven investigator research.

Over the past 20 years, we have learned that exoplanets are ubiquitous throughout our Galaxy and show a diverse set of demographics, yet there is much work to be done to understand this diversity. Determining the distributions of the fundamental properties of exoplanets will provide vital clues regarding their formation and evolution. This is a difficult task, as exoplanet surveys are not uniformly sensitive to the full range of planet parameter space. Various observational biases and selection effects intrinsic to each of the different discovery techniques constrain the types of planets to which they are sensitive. Herein, I record a collection of the first studies to develop and apply the methodology of synthesizing results from multiple detection techniques to construct a statistically-complete census of planetary companions to M dwarfs that samples a wide region of their parameter space.

The discovery of thousands of transiting exoplanet candidates by NASA's Kepler mission revolutionized the study of exoplanets, shifting the field beyond the characterization of individual systems towards mapping the true distribution of all planetary systems and probing population-level trends. Inferring the underlying architectures of planetary systems from the Kepler data requires a detailed understanding of the detection pipeline and statistical methods. In this dissertation, I combine a forward modeling framework (SysSim) with approximate Bayesian computation to develop and test population models for the intrinsic distributions of planetary systems. The properties of both single and multi-transiting systems can be combined to make powerful inferences on the underlying inter- and intra-system correlations. I define a series of distance functions for comparing models to the Kepler data, including the distributions of observed multiplicities, period ratios, transit depth ratios, and transit duration ratios, as well as complexity metrics designed to capture system-level patterns. I also train a Gaussian process emulator for rapidly constraining model posterior distributions. In separating detection biases from the physical patterns, I show evidence for the "peas-in-a-pod" patterns: that planets in multi-planet systems tend to be highly clustered in their radii, show a preferential size ordering, and exhibit remarkably uniform spacings. I also show that inner planetary systems are more common around later type stars across FGK dwarfs, although their architectures may be similar. By parameterizing the mutual inclination distribution using Rayleigh distributions, I show that a mixture of a low and a high mutual inclination population is necessary to fit the Kepler-observed multiplicity distribution. I then describe a method of drawing clustered planetary systems at the angular momentum deficit (AMD) stability limit. This maximum AMD model produces additional correlations between the orbital excitations (eccentricities and mutual inclinations) and the multiplicities of each system. These results lead to observational predictions that are seen in the transit duration ratios and the number of transit duration variation detections, clarifying the long-standing "Kepler dichotomy" problem (an apparent excess of transiting singles) and providing a link to its dynamical nature. Finally, I demonstrate how our knowledge of population-wide architectures can be leveraged to make predictions about the presence of additional planets conditioned on a given (e.g., transiting) planet. While unseen planets may be discovered with additional methods and provide a more complete picture of a system's architecture, they can also hinder the interpretation of known planets in radial velocity (RV) data. I perform simulations of RV surveys to quantify how many additional observations are needed to accurately measure the semi-amplitude of transiting planets, which is the standard strategy for follow-up characterization of planets from the TESS mission.

To understand the uniqueness of our solar system, we must assess the system architectures and demographic features existing in the known planet population, but such a task requires a homogeneous set of candidates. Fortunately, the Kepler spacecraft continuously collected photometry from a single patch of the sky, which in turn produced a well characterized catalog of transiting exoplanets. However, previous studies assumed multi-planet systems were subject to the same selection effects as their single-planet counterparts. I investigate this assumption, finding that a proper completeness accounting significantly increases the underlying occurrence of multi-planet systems to 5.86 planets per FGK dwarf and only requires a 1.5 degree average system mutual inclination. Using this correction I provide an updated extrapolation of the occurrence of Earth analogs and find that 5.9% of GK dwarfs have more than one planet within their habitable zone. Additionally, the K2 mission collected photometry from 18 fields along the ecliptic plane, providing a unique opportunity to understand how exoplanet formation may be affected by galactic latitude, stellar metallicity, and stellar age. For my thesis, I developed a fully automated pipeline able to detect and vet transit signals in K2 photometry, enabling assessment of sample completeness and reliability. This catalog contains 768 planets, with 235 newly identified candidates. Correspondingly, I present the first uniform analysis of small transiting exoplanet occurrence outside of the Kepler field, finding a metallicity dependence in small planet occurrence. I also discuss how the Sun's late stage evolution and the existing solar system architecture will capture Jupiter and Saturn into a mean-motion resonance. Eventually perturbations from passing stars will trigger large-scale instability, culminating in the disassociation of all outer planets. Extrapolating this result to other systems indicates a temporal dependence on bound planet occurrence in the Galaxy.

This book is a compendium of key scientific questions, challenges, and opportunities across different areas of exoplanetary science. The field is currently experiencing rapid growth, and the book provides a front-row view of the advancements at the cutting-edge of the field. Each chapter contains a short exposition on the most important open questions, challenges, and opportunities in a specific area from the perspective of one or more top experts in the area. It provides a starting point for researchers, experts and non-experts alike, to obtain a quick overview of the forefront of exoplanetary science and a vision for the future of the field. Topics range from observational developments and techniques, including exoplanet detection and characterisation methods and state-of-the-art and future missions, to exoplanet theory and modelling including planet formation, planetary interiors, atmospheres, habitability and the search for life. Key Features Provides a close-up view of the frontiers of exoplanetary science research Summarises key questions, challenges, and opportunities across different areas of the field Written by leading experts in the field Provides a valuable reference for early career researchers Topics span from state-of-the-art and emerging areas to long-term future directions

An unprecedented number of planets outside of the solar system have been found, with an explosion in the number of discoveries in recent years. Find out what has been happening in this rapidly advancing arena of human exploration, what these extrasolar planets are like, and why some traditional ideas face being thrown out.

In 1988, in an article on the analysis of the measurements of the variations in the radial velocities of a number of stars, Campbell, Walker, and Yang reported an - teresting phenomenon;the radial velocity variations of Cephei seemed to suggest the existence of a Jupiter-like planet around this star. This was a very exciting and, at the same time, very surprising discovery. It was exciting because if true, it would have marked the detection of the ?rst planet outside of our solar system. It was surprising because the planet-hosting star is the primary of a binary system with a separation less than 19 AU, a distance comparable to the planetary distances in our solar system. The moderatelyclose orbit of the stellar companionof Cephei raised questions about the reality of its planet. The skepticism over the interpretation of the results (which was primarily based on the idea that binary star systems with small sepa- tions would not be favorable places for planet formation) became so strong that in a subsequent paper in 1992, Walker and his colleagues suggested that the planet in the Cephei binary might not be real, and the variations in the radial velocity of this star might have been due to its chromospheric activities.

Topics covered include comparative planetology on worlds near and far; solar system studies as a baseline to inform studies of extrasolar planetary properties and evolution; and lessons learned on planetary statistics, demographics, and system architectures from extrasolar planetary systems.