Habitability of Super-Earth Planets around Main-Sequence Stars including Red Giant Branch Evolution: Models based on the Integrated System Approach

摘要

In a previous study published in Astrobiology, we focused on the evolution ofhabitability of a 10 M_E super-Earth planet orbiting a star akin to the Sun.This study was based on a concept of planetary habitability in accordance tothe integrated system approach that describes the photosynthetic biomassproduction taking into account a variety of climatological, biogeochemical, andgeodynamical processes. In the present study, we pursue a significantaugmentation of our previous work by considering stars with zero-age mainsequence masses between 0.5 and 2.0 M_sun with special emphasis on models of0.8, 0.9, 1.2 and 1.5 M_sun. Our models of habitability consider againgeodynamical processes during the main-sequence stage of these stars as well asduring their red giant branch evolution. Pertaining to the different types ofstars, we identify so-called photosynthesis-sustaining habitable zones (pHZ)determined by the limits of biological productivity on the planetary surface.We obtain various sets of solutions consistent with the principal possibilityof life. Considering that stars of relatively high masses depart from themain-sequence much earlier than low-mass stars, it is found that the biosphericlife-span of super-Earth planets of stars with masses above approximately 1.5M_sun is always limited by the increase in stellar luminosity. However, forstars with masses below 0.9 M_sun, the life-span of super-Earths is solelydetermined by the geodynamic time-scale. For central star masses between 0.9and 1.5 M_sun, the possibility of life in the framework of our models dependson the relative continental area of the super-Earth planet.