Origins of life and evolution of the biosphere

, Volume 27, Issue 4, pp 413-420

First online:

ultraviolet radiation from F and K stars and implications for planetary habitability

  • James F. KastingAffiliated withDepartment of Geosciences, The Pennsylvania State University
  • , Douglas C. B. WhittetAffiliated withDepartment of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute
  • , William R. SheldonAffiliated withPhysics Department, University of Houston

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Now that extrasolar planets have been found, it is timely to ask whether some of them might be suitable for life. Climatic constraints on planetary habitability indicate that a reasonably wide habitable zone exists around main sequence stars with spectral types in the early-F to mid-K range. However, it has not been demonstrated that planets orbiting such stars would be habitable when biologically-damaging energetic radiation is also considered. The large amounts of UV radiation emitted by early-type stars have been suggested to pose a problem for evolving life in their vicinity. But one might also argue that the real problem lies with late-type stars, which emit proportionally less radiation at the short wavelengths (λ < 200 nm) required to split O2 and initiate ozone formation. We show here that neither of these concerns is necessarily fatal to the evolution of advanced life: Earth-like planets orbiting F and K stars may well receive less harmful UV radiation at their surfaces than does the Earth itself.