Kepler-452b is currently the best example of an Earth-size planet in the habitable zone of a sun-like star , a type of planet whose number of detections is expected to increase in the future .
Searching for biosignatures in the supposedly thin atmospheres of these planets is a challenging goal that requires a careful selection of the targets .
Under the assumption of a rocky-dominated nature for Kepler-452b , we considered it as a test case to calculate a temperature-dependent habitability index , h _ { 050 } , designed to maximize the potential presence of biosignature-producing activity ( Silva et al .
2016 ) .
The surface temperature has been computed for a broad range of climate factors using a climate model designed for terrestrial-type exoplanets ( Vladilo et al .
2015 ) .
After fixing the planetary data according to the experimental results ( Jenkins et al .
2015 ) , we changed the surface gravity , CO _ { 2 } abundance , surface pressure , orbital eccentricity , rotation period , axis obliquity and ocean fraction within the range of validity of our model .
For most choices of parameters we find habitable solutions with h _ { 050 } > 0.2 only for CO _ { 2 } partial pressure p _ { \mathrm { CO _ { 2 } } } \lesssim 0.04 bar .
At this limiting value of CO _ { 2 } abundance the planet is still habitable if the total pressure is p \lesssim 2 bar .
In all cases the habitability drops for eccentricity e \gtrsim 0.3 .
Changes of rotation period and obliquity affect the habitability through their impact on the equator-pole temperature difference rather than on the mean global temperature .
We calculated the variation of h _ { 050 } resulting from the luminosity evolution of the host star for a wide range of input parameters .
Only a small combination of parameters yield habitability-weighted lifetimes \gtrsim 2 Gyr , sufficiently long to develop atmospheric biosignatures still detectable at the present time .