The TOASHI multi-parameter habitability index provides a comprehensive metric for extrasolar worlds

Abstract This study introduces a planetary habitability index for exoplanets. Prior to defining the index, we analysed planetary and stellar factors that influence habitability. We reviewed existing indices and identified five sub-indices incorporating the most relevant parameters. Habitability is defined as a planet’s potential to support life, primarily determined by the presence of surface liquid water. Our index is a multiparametric score calculated as the geometric mean of several characteristics: the planet’s geophysical properties; its orbital parameters including orbital period, eccentricity, and the tidal effects; and stellar attributes, such as host star age, metallicity and incorporating a magnetic field criterion. We represent the continuous variables by an individual probability derived from a likelihood function that will be applied to the index. With respect to the parameters, the novelty of this index lies in calculating the tidal effect as a function of stellar age and in our approach to estimating stellar magnetism from the Alfvén surface. The planet’s position within its star’s habitable zone is also considered. Owing to current limitations in exoplanetary data, not all parameters are available for every confirmed exoplanet. We therefore computed the index for 588 exoplanets with complete datasets, out of NASA’s 5,867 confirmed at the moment of the study. The index ranges from 0 to 1, with Earth assigned a reference value of 1. Application of the index identified nine exoplanets with scores above 0, highlighting their potential habitability.