Potential Habitability as a Stellar Property: Assessing the Habitable Histories of Stellar Systems
Open Access
- Author:
- Tuchow, Noah
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 28, 2022
- Committee Members:
- Steinn Sigurdsson, Major Field Member
Michael Eracleous, Major Field Member
Jason Wright, Chair & Dissertation Advisor
Eric Ford, Major Field Member
James Kasting, Outside Unit & Field Member
Rebekah Dawson, Program Head/Chair - Keywords:
- Exoplanets
Astrobiology
Exoplanet Evolution
Biosignatures
Direct Imaging
Planet hosting stars
Habitable zone
Stellar properties - Abstract:
- Future missions to directly image exoplanets aim to measure the spectra of Earth-like planets in the habitable zones of their stars to infer their atmospheric compositions and search for biosignatures. In addition to selecting target stars to maximize the number of Earth-like planets that will be discovered and characterized, future missions should also take the long-term habitability of these planets into account and use this as a means to infer whether planets would be likely to host signs of life. It is essential to consider whether a planet has been consistently habitable throughout its history or if it only became habitable recently and entered the habitable zone due to the host star’s evolution. I term this latter class of planets Belatedly Habitable Planets, and emphasize that their habitability remains ambiguous and a rich area for future research. I have developed a framework for computing relative biosignature yields among potential target stars, given a model of habitability and biosignature genesis, and planetary occurrence rates. For different model choices, I find that the stellar populations preferred by my metrics vary drastically in terms of stellar masses and ages. The most physically motivated models for biosignature occurrence depend on the duration that a planet has been habitable, which requires precise stellar evolutionary tracks to accurately assess. I analyze the sensitivity of my biosignature yield metrics and other derived stellar properties, such as masses and ages, to stellar model uncertainties and systematic uncertainties in observed stellar properties. I determine the required precision needed to rank target stars according to my long-term habitability metrics and the extent to which obtaining more precise stellar properties decreases the uncertainty in relative biosignature yields.