Solar UV irradiation conditions on the surface of Mars

Photochemistry and Photobiology, Jan 2003 by Ronto, Gyorgyi, Berces, Attila, Lammer, Helmut, Cockell, Charles S, Et al

The high-pressure values are based on extreme atmospheric sputtering loss rates (7,8). Recent, more complex 3-D Monte Carlo models show that former 1-D-based atmospheric escape models resulted in overestimated sputtering yields (10). We use therefore the more moderate loss rates, which are close to I bar total atmospheric loss as inputs for our study concerning the UV protection of the Martian surface during the past 3.5 Gyr.

After 3.5 Gyr common nonthermal atmospheric loss studies become uncertain because additional processes such as heavy asteroid bombardment and a much more active early Sun produce feedback effects, which are not easy to model (10). We include in our study for the ancient Martian atmosphere a photochemical model for the calculation of UV absorbing atmospheric constituents (37,39,40). The codes used in our model were originally developed for ESA's Darwin and National Aeronautics and Space Administration's Terrestrial Planet Finder projects, aimed at the detection of extrasolar terrestrial planets and some of their atmospheric components (40). In particular, both space telescopes will be sensitive to the 9.6 pm band of O^sub 3^, thought to be the signature of an O2-rich atmosphere produced by photosynthetic life forms. Their study also investigated whether O2 and O^sub 3^ can also be produced by photochemical reactions. For this purpose a new photochemical and radiative-convective model of terrestrial planetary atmospheres incorporating a 1 bar Martian CO2 atmosphere was developed (39,40).

Acknowledgements-Gy. Ronto, A. Berces and H. Lammer thank the Os terreichischer Akademischer Austauschdienst (OAD) for supporting thin work that is part of the Austrian-Hungarian OAD-project A-20/2000: Ef feet of Extraterrestrial Radiation on Molecules essential for Life.

1Posted on the website on 25 November 2002.

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