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Register a new userQuantitative estimates of the surface habitability of Kepler-452b
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Laura Silva
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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.
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