Earth Similarity Index and Habitability Studies of Exoplanets

Abstract: Study of exoplanets has been of considerable interest for Astronomers, Planetary Scientists and Astrobiologists. Analysis of huge planetary data from space missions such as CoRoT and Kepler is directed ultimately at finding a planet similar to Earth- the Earth's twin, and looking for potential habitability. The Earth Similarity Index (ESI) is defined to find the similarity with Earth, which ranges from 1 (Earth) to 0 (totally dissimilar to Earth). ESI can be computed using four physical parameters of a planet, namely radius, density, escape velocity and surface temperature. The surface temperature entering surface ESI is a non-observable quantity and what we know is only equilibrium temperature of exoplanets. We have established a relation between surface and equilibrium temperatures using the data available for the solar system objects to address the difficulty in determining surface temperature. From the ESI analysis, we have found 20 Earth-like exoplanets with ESI value above 0.8, which is set as the threshold. We are also interested in Mars-like planets to search for planets that may host the extreme life For example, methane-specific extremophile life form metabolism, for which a new approach, called Mars Similarity Index (MSI) is introduced. MSI is defined in the range between 1 (present Mars) and 0 (dissimilar to present Mars) and uses the same physical parameters as that of ESI. We introduced another new approach to study the potential habitability of exoplanets based on Cobb-Douglas Function, multi-parametric function. This did not yield any encouraging results.