title: Ultraviolet radiation from F and K stars and implications for planetary habitability.
abstract: 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 (lambda < 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.
authors.affiliation: Department of Geosciences, The Pennsylvania State University, University Park 16802, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Kasting
authors.forename: D C
authors.initials: DC
authors.lastname: Whittet
authors.forename: W R
authors.initials: WR
authors.lastname: Sheldon
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D001272:Atmosphere / Q000737:chemistry*; D019419:Evolution, Planetary; D005118:Extraterrestrial Environment; D008956:Models, Chemical; D010100:Oxygen / Q000032:analysis; D010126:Ozone / Q000032:analysis; D010777:Photochemistry; D016083:Planets; D014466:Ultraviolet Rays
chemical_list: D010126:Ozone; D010100:Oxygen