International Journal of Astrobiology

Seasonal and diurnal variations in Martian surface ultraviolet irradiation: biological and chemical implications for the Martian regolith

M. R. Patel a1c1, A. Bérces a2, C. Kolb a3, H. Lammer a3, P. Rettberg a4, J. C. Zarnecki a1 and F. Selsis a5
a1 Planetary and Space Sciences Research Institute, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK e-mail:
a2 MTA-SE Research Group for Biophysics, Semmelweis Med. University, VIII Puskin u.9, H-1444 Budapest, Hungary
a3 Space Research Institute, Department for Extraterrestrial Physics, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042, Graz, Austria
a4 German Aerospace Centre (DLR), Institute of Aerospace Medicine, 51170 Cologne, Germany
a5 Centro de Astrobiologia (CSIC/INTA), Carretera Ajalvier, km 4, Torrejón de Ardoz, Madrid, Spain


The issue of the variation of the surface ultraviolet (UV) environment on Mars was investigated with particular emphasis being placed on the interpretation of data in a biological context. A UV model has been developed to yield the surface UV irradiance at any time and place over the Martian year. Seasonal and diurnal variations were calculated and dose rates evaluated. Biological interpretation of UV doses is performed through the calculation of DNA damage effects upon phage T7 and Uracil, used as examples for biological dosimeters. A solar UV ‘hotspot’ was revealed towards perihelion in the southern hemisphere, with a significant damaging effect upon these species. Diurnal profiles of UV irradiance are also seen to vary markedly between aphelion and perihelion. The effect of UV dose is also discussed in terms of the chemical environment of the Martian regolith, since UV irradiance can reach high enough levels so as to have a significant effect upon the soil chemistry. We show, by assuming that H2O is the main source of hydrogen in the Martian atmosphere, that the stoichiometrically desirable ratio of 2:1 for atmospheric H and O loss rates to space are not maintained and at present the ratio is about 20:1. A large planetary oxygen surface sink is therefore necessary, in contrast with escape to space. This surface oxygen sink has important implications for the oxidation potential and the toxicology of the Martian soil. UV-induced adsorption of {\rm O}_{2}^{-} super-radicals plays an important role in the oxidative environment of the Martian surface, and the biologically damaging areas found in this study are also shown to be regions of high subsurface oxidation. Furthermore, we briefly cover the astrobiological implications for landing sites that are planned for future Mars missions.

(Received April 4 2002)
(Accepted November 11 2002)

Key Words: biologically effective dose; DNA damage; landing sites; Mars; radiation climate; radiative transfer; regolith; toxicology; UV.

c1 Corresponding author.