S. Francka, W. von Bloha, C. Bounamaa, M. Steffenb, D. Schönbernerb, and H.-J. Schellnhubera
J. Geophys. Res. 105, no. E1, 1651-1658 (2000)
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.
A general modeling scheme for assessing the suitability for life of extrasolar planets is presented.
The scheme focuses on the identification of the "habitable zone" in main-sequence star
planetary systems accommodating Earth-like components. Our definition of habitability is
based on the long-term possibility of photosynthetic biomass production under geodynamic
conditions. Therefore, all the pertinent astrophysical, climatological, biogeochemical, and
geodynamic 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. A geostatic model version is developed and investigated in parallel for demonstration
purposes. The numerical solution of the advanced geodynamic model yields realistic
look-up diagrams for convenient habitability determination. As an illustration, the MACHO-98-BLG-35 event is scrutinized. It is shown that this event is definitely not tantamount to the
discovery of one of Gaia's sisters.
Full text of article incl. figures in PDF-format (380 KByte).
Figure: Shape of the GDM-HZ (green shading) in the mass-time plane for an Earth-like
planet at distance R = 2 AU from the central star. The potential overall domain for
accommodating the HZ for planets at some arbitrary distance is limited by a number of
factors that are independent of R: (I) Minimum time for biosphere development (tH<0.8 Gyr excluded); (II) Central-star life time on the main sequence (t>tH excluded); (III)
Geodynamics of the Earth-like planet (t>tmax excluded); (IV) Tidal locking of the planet
(non-trivial sub-domain excluded). The excluded realms are marked by grey shading in case
of the first three factors, and by grey hatching for the tidal-locking effect. The horizontal red
line represents the probable "life time" of the hypothetical MACHO-98-BLG-35 planet,
which is assumed to orbit a 0.3 MS star.