S. Francka, M. Cuntzb, W. von Bloha, and C. Bounamaa
International Journal of Astrobiology, 2, 35-39 (2003)
aPotsdam Institute for Climate Impact Research (PIK),
Telegrafenberg, P.O. Box 60 12 03,
14412 Potsdam, Germany.
bDepartment of Physics, University of Texas at
Arlington, Box 19059, Arlington, TX 76019, USA.
In a previous paper, we showed that Earth-type
habitable planets around 47 UMa are in principle possible if
a distinct set of conditions is warranted. These conditions
include that the Earth-type planets have successfully formed and
are orbitally stable and, in addition, that the 47 UMa star-planet
system is relatively young (< 6 Gyr). We now extend this study
by considering Earth-like planets with different land / ocean coverages.
This study is again based on the so-called integrated system approach,
which describes the photosynthetic biomass production taking into account
a variety of climatological, biogeochemical, and geodynamical processes.
This approach implies a special characterization of the habitable
zone defined for a distinct type of planet. We show that the likelihood
to find a habitable Earth-like planet on a stable orbit around 47 UMa critically
depends on the percentage of the planetary land / ocean coverage.
The likelihood is significantly increased for planets with
a very high percentage of ocean surface ("water worlds").
Keywords: Extrasolar planets, geodynamics, habitable zone, orbital stability and planetary climate.
Figure: The habitable zone around 47 UMa for the likely value of luminosity
of L=1.54 Ls. The colored areas indicate the extent of the HZ for different
relative continental areas. The grey shaded area indicates the permissible
parameter space as constraint by the stellar age and the orbital stability limit
at 1.25 AU.