S. Franck^a, W. von Bloh^a, C. Bounama^a, M. Steffen^b, D. Schönberner^b, and H.-J. Schellnhuber^a

Adv. Space Res. 28/4, 695-700 (2001)

^aPotsdam Institute for Climate Impact Research (PIK), Telegrafenberg, P.O. Box 60 12 03, 14412 Potsdam, Germany.

^bAstrophysikalisches Institut Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany.

Abstract

We present a general modelling scheme for investigating the possibility of photosynthesis-based life on extrasolar planets. The scheme focuses on the identification of the habitable zone main-sequence-star planetary systems with planets of Earth mass and size. Our definition of habitability is based on the long-term possibility of photosynthetic biomass production as a function of mean planetary surface temperature and atmospheric CO₂-content. All the astrophysical, climatological, biogeochemical, and geodynamic key processes involved in the generation of photosynthesis-driven life conditions are taken into account. Implicitly, a co-genetic origin of the central star and the orbiting planet is assumed. The numerical solution of an advanced geodynamic model yields realistic look-up diagrams for determing the limits of photosynthesis in extrasolar planetary systems, assuming minimum CO₂ levels set by demand of C₄ photosynthesis.

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Figure: Width and position of the HZ (shaded) as a function of time for three different central-star masses (M=0.8, 1.0, 1.2 M_s) for an Earth-like planet. R_opt is the optimum position with maximum life span of the photosynthesis-based biosphere.