A Flexible Bayesian Framework for Assessing Habitability with Joint Observational and Model Constraints

The catalog of stellar evolution tracks discussed in our previous work is meant to help characterize exoplanet host stars of interest for follow-up observations with future missions like the James Webb Space Telescope. However, the utility of the catalog has been predicated on the assumption that we would precisely know the age of the particular host star in question; in reality, it is unlikely that we will be able to accurately estimate the age of a given system. Stellar age is relatively straightforward to calculate for stellar clusters, but it is difficult to accurately measure the age of an individual star to high precision. Unfortunately, this is the kind of information we should consider as we attempt to constrain the long-term habitability potential of a given planetary system of interest. This is ultimately why we must rely on predictions of accurate stellar evolution models, as well a consideration of what we can observably measure (stellar mass, composition, orbital radius of an exoplanet) in order to create a statistical framework wherein we can identify the best candidate systems for follow-up characterization. In this paper we discuss a statistical approach to constrain long-term planetary habitability by evaluating the likelihood that at a given time of observation, a star would have a planet in the 2 Gy continuously habitable zone (CHZ₂). Additionally, we will discuss how we can use existing observational data (i.e., data assembled in the Hypatia catalog and the Kepler exoplanet host star database) for a robust comparison to the catalog of theoretical stellar models.