Exploring the habitability and interior composition of exoplanets lying within the extended habitable zone

ABSTRACT Studying the habitability, internal structure, and composition of exoplanets is crucial for understanding their potential to sustain life beyond our Solar system. Characterizing planetary structures and atmospheric evolution provides valuable insights into surface conditions and the long-term habitability of these planets. In this study, we present a comprehensive analysis of exoplanets spanning from super-Earths to mini-Neptunes ($R_{\textrm {p}}$ $\le$ 4 $R_{\rm{\oplus }}$ and $M_{\textrm {p}}$ $\le$ 15 $M_{\rm{\oplus }}$) located within the extended habitable zone, along with parametrization of their host stars. We find that the planets in our sample orbit M dwarf stars and are tidally locked to them. Using archival photometric data from Gaia, Pan-STARRS1, 2MASS, and WISE, we estimate the atmospheric and physical parameters of the host stars. We also model the interior structure of these planets to infer their possible compositions. Additionally, under the assumption that these exoplanets can accrete a gaseous layer, we model the envelope fraction of the habitable exoplanets. With an Earth-like rocky composition, LHS 1140 b and TOI-1452 b can hold on to negligible amount of their initial gas layer. However, sustaining a sufficient amount of atmosphere over time, the planets LP 791-18 c, LTT 3780 c, and K2-18 b are likely to be water worlds. The models suggest a water-rich composition for TOI-1266 c without any significant amount of atmosphere. Modelling interior compositions and atmospheric escape scenarios allows us to assess the potential habitability of these planets by evaluating the likelihood of surface liquid water and the retention of stable atmospheres.