Study of exoplanets is one of the main goals
of present research in planetary sciences and astrobiology.
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 answering the ques-
tion of potential exo-habitability. The Earth Similarity Index
(ESI) is a first step in this quest, ranging from 1 (Earth) to 0
(totally dissimilar to Earth). It was defined for the four phys-
ical parameters of a planet: radius, density, escape velocity
and surface temperature. The ESI is further sub-divided into
interior ESI (geometrical mean of radius and density) and
surface ESI (geometrical mean of escape velocity and sur-
face temperature). The challenge here is to determine which
exoplanet parameter(s) is important in finding this similar-
ity; how exactly the individual parameters entering the inte-
rior ESI and surface ESI are contributing to the global ESI.
Since the surface temperature entering surface ESI is a non-
observable quantity, it is difficult to determine its value. Us-
ing the known data for the Solar System objects, we estab-
lished the calibration relation between surface and equilib-
rium temperatures to devise an effective way to estimate the
value of the surface temperature of exoplanets.
B J.M. Kashyap
kas7890.astro@gmail.com
S.B. Gudennavar
shivappa.b.gudennavar@christuniversity.in
U. Doshi
urmi84@gmail.com
M. Safonova
margarita.safonova62@gmail.com
1 Department of Physics, Christ University, Bengaluru 560 029,
India
2 M.P. Birla Institute of Fundamental Research, Bangalore
560 001, India
ESI is a first step in determining potential exo-habitability
that may not be very similar to a terrestrial life. A new ap-
proach, called Mars Similarity Index (MSI), is introduced
to identify planets that may be habitable to the extreme
forms of life. MSI is defined in the range between 1 (present
Mars) and 0 (dissimilar to present Mars) and uses the same
physical parameters as ESI. We are interested in Mars-like
planets to search for planets that may host the extreme life
forms, such as the ones living in extreme environments on
Earth; for example, methane on Mars may be a product of
the methane-specific extremophile life form metabolism.

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• Indexing of exoplanets in search for potential habitability: application to Mars-like worlds