Publisher
The University of Arizona.Rights
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.Abstract
The field of exoplanet astronomy is advancing toward the atmospheric characterization of Earth-like planets around nearby stars, with the ultimate goal of probing these exoplanets for evidence of life. Yet despite requiring the development of telescopes and measuring devices with unprecedented size and precision, this effort will yield only a fraction of the information content per planet afforded by robotic explorations of Solar System bodies. Given the diversity of terrestrial worlds within the Solar System, we can expect to face significant ambiguity in understanding the habitability and histories of potential exo-Earths, including potential "false positive" signatures of life. Given such limited data, how can we hope to determine which worlds are habitable or inhabited, or to understand more generally what factors make a planet habitable and give rise to life? In this thesis, I propose solutions to this problem which draw upon the unique statistical advantage offered by their sheer numbers and the wide range of planetary properties they present. First, I demonstrate how existing knowledge about the frequency and sizes of terrestrial planets can be used to probabilistically constrain the composition of Proxima Centauri b - a nearby planet for which we have few direct measurements - and find that it is quite likely to be a terrestrial planet. Next, I demonstrate how a similar approach could be combined with future direct imaging observations of nearby stellar systems to determine which of their planets are most likely to be potentially habitable. This optimized target selection strategy could save weeks to months of follow-up observing time on a flagship-class space telescope. Following that, I present my analysis of the transit spectrum of WASP-4b, in which I approach the critical unresolved issue of stellar contamination which could limit the usefulness of this technique for studying habitable exoplanets in the future. My Bayesian evidence-based approach presents a possible solution for future analyses. In the final chapters, I focus on developing testable statistical hypotheses for future surveys of habitable exoplanets which would shed light on how these worlds form and evolve. I begin by proposing that a correlation might exist between the ages of habitable planets and the fraction which have oxygen, which I dub the "age-oxygen correlation". A successful test of this hypothesis would demonstrate that other inhabited planets evolve in similar ways to Earth, and would suggest that atmospheric O2 can be interpreted as robust evidence of life. Next, I expand in this direction by developing a general framework for evaluating the potential of next-generation space telescopes to test statistical hypotheses such as these. I apply the framework to demonstrate the requirements for an observatory to detect the existence of the habitable zone and constrain its boundaries, as well as to measure the timescale of atmospheric evolution on Earth-like planets. Finally, I condense my results into key recommendations for future efforts to study habitable exoplanets and search for life beyond the solar system.Type
textElectronic Dissertation
Degree Name
Ph.D.Degree Level
doctoralDegree Program
Graduate CollegeAstronomy and Astrophysics