  Nowadays, we know thousands of exoplanets, some of them potentially
habitable. Next technological facilities (JWST, for example) have exoplanet
atmosphere analysis capabilities, but they also have limits in terms of how
many targets can be studied. Therefore, there is a need to rank and prioritize
these exoplanets with the aim of searching for biomarkers. Some criteria
involved, such as the habitability potential of a dry-rock planet versus a
water-rich planet, or a potentially-locked planet versus a tidally-locked
planet, are often vague and the use of the fuzzy set theory is advisable. We
have applied a combination of Multi-Criteria Decision-Making methodologies with
fuzzy logic, the Fuzzy Reference Ideal Method (FRIM), to this problem. We have
analyzed the habitability potential of 1798 exoplanets from TEPCat database
based on a set of criteria (composition, atmosphere, energy, tidal locking,
type of planet and liquid water), in terms of their similarity to the only
ideal alternative, The Earth. Our results, when compared with the probability
index SEPHI, indicate that Kepler-442b, Kepler-062e/f, and LHS_1140b are the
best exoplanets for searching for biomarkers, regardless its technical
difficulty. If we take into account current technical feasibility, the best
candidate is TRAPPIST-1e.
