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Published Online: 5 July 2004

Ozone Concentrations and Ultraviolet Fluxes on Earth-Like Planets Around Other Stars

Publication: Astrobiology
Volume 3, Issue Number 4

Abstract

Coupled radiative-convective/photochemical modeling was performed for Earth-like planets orbiting different types of stars (the Sun as a G2V, an F2V, and a K2V star). O2 concentrations between 1 and 10-5 times the present atmospheric level (PAL) were simulated. The results were used to calculate visible/near-IR and thermal-IR spectra, along with surface UV fluxes and relative dose rates for erythema and DNA damage. For the spectral resolution and sensitivity currently planned for the first generation of terrestrial planet detection and characterization missions, we find that O2 should be observable remotely in the visible for atmospheres containing at least 10-2 PAL of O2. O3 should be visible in the thermal-IR for atmospheres containing at least 10-3 PAL of O2. CH4 is not expected to be observable in 1 PAL O2 atmospheres like that of modern Earth, but it might be observable at thermal-IR wavelengths in "mid-Proterozoic-type" atmospheres containing ~ 10-1 PAL of O2. Thus, the simultaneous detection of both O3 and CH4 - considered to be a reliable indication of life - is within the realm of possibility. High-O2 planets orbiting K2V and F2V stars are both better protected from surface UV radiation than is modern Earth. For the F2V case the high intrinsic UV luminosity of the star is more than offset by the much thicker ozone layer. At O2 levels below ~ 10-2 PAL, planets around all three types of stars are subject to high surface UV fluxes, with the F2V planet exhibiting the most biologically dangerous radiation environment. Thus, while advanced life is theoretically possible on high-O2 planets around F stars, it is not obvious that it would evolve as it did on Earth.

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Published In

cover image Astrobiology
Astrobiology
Volume 3Issue Number 4December 2003
Pages: 689 - 708
PubMed: 14987475

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Published online: 5 July 2004
Published in print: December 2003

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Antígona Segura
Department of Geosciences, Pennsylvania State University, State College, Pennsylvania
Kara Krelove
Department of Geosciences, Pennsylvania State University, State College, Pennsylvania
James F. Kasting
Department of Geosciences, Pennsylvania State University, State College, Pennsylvania
Darrell Sommerlatt
Department of Geosciences, Pennsylvania State University, State College, Pennsylvania
Victoria Meadows
NASA Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California
David Crisp
NASA Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California
Martin Cohen
Radio Astronomy Laboratory, University of California, Berkeley, California
Eli Mlawer
Atmospheric and Environmental Research, Inc., Lexington, Massachusetts

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