2017MNRAS.471.4628R

A new index, the Statistical-likelihood Exo-Planetary Habitability Index (SEPHI), is presented. It has been developed to cover the current and future features required for a classification scheme disentangling whether any exoplanet discovered is potentially habitable compared with life on Earth. SEPHI uses likelihood functions to estimate the habitability potential. It is defined as the geometric mean of four sub-indexes related to four comparison criteria: Is the planet telluric? Does it have an atmosphere dense enough and a gravity compatible with life? Does it have liquid water on its surface? Does it have a magnetic field shielding its surface from harmful radiation and stellar winds? SEPHI can be estimated with only seven physical characteristics: planetary mass, planetary radius, planetary orbital period, stellar mass, stellar radius, stellar effective temperature and planetary system age. We have applied SEPHI to all the planets in the Exoplanet Encyclopaedia using a Monte Carlo method. Kepler-1229b, Kepler-186f and Kepler-442b have the largest SEPHI values assuming certain physical descriptions. Kepler-1229b is the most unexpected planet in this privileged position since no previous study pointed to this planet as a potentially interesting and habitable one. In addition, most of the tidally locked Earth-like planets present a weak magnetic field, incompatible with habitability potential. We must stress that our results are linked to the physics used in this study. Any change in the physics used implies only an updating of the likelihood functions. We have developed a web application allowing the online estimation of SEPHI (http://sephi.azurewebsites.net/).