Sterilization of Martian surface by cosmic radiation

Abstract A problem connected with a search for life or traces of life on Mars is studied, namely, the radiation sterilization of the planet surface. Physical conditions on Martian surface now and in its former times as well as types of influencing radiation are analyzed. We show that the average dose intensity in the upper meters of Martian soil is not dangerous for living microorganisms. However, sterilization of microorganisms in the dormancy state, modeled by terrestrial radio-resistant D. radiodurans, would occur in the upper 20 g cm −2 in less then 30 thousand years. The dormant life would be killed in the layer down to about 700 g cm −2 by the galactic cosmic rays in a time period less then 2×10 6 yr and below this level by the long–lived radioactivity in about 4×10 7 yr . Destructive influence of cosmic radiation could also significantly change the mean atomic mass of hypothetical Martian fossil macromolecules and 13C/12C ratio in organic material. A conclusion is drawn that the most promising locations for the search for life or its traces on the Martian surface are the polar caps.

[1]  M. Malin,et al.  Evidence for recent groundwater seepage and surface runoff on Mars. , 2000, Science.

[2]  G. Flynn.  The delivery of organic matter from asteroids and comets to the early surface of Mars , 1996 .

[3]  W. Ward.  Present obliquity oscillations of Mars: Fourth‐order accuracy in orbital e and I , 1979 .

[4]  J. Battista,et al.  Against all odds: the survival strategies of Deinococcus radiodurans. , 1997, Annual review of microbiology.

[5]  Carl Sagan,et al.  Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life , 1992, Nature.

[6]  J. Masarik,et al.  Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere , 1999 .

[7]  I. Iori,et al.  Study of (p, α) reactions in light nuclei at 38 MeV , 1969 .

[8]  R. Zare,et al.  Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 , 1996, Science.

[9]  A. Earl,et al.  Why is Deinococcus radiodurans so resistant to ionizing radiation? , 1999, Trends in microbiology.

[10]  Solar Modulation Effects in Terrestrial Production of Carbon-14 , 1980 .

[11]  D. R. Rushneck,et al.  The search for organic substances and inorganic volatile compounds in the surface of Mars , 1977 .

[12]  G. Horneck,et al.  Natural Transfer of Viable Microbes in Space: 1. From Mars to Earth and Earth to Mars , 2000 .

[13]  M. Hecht,et al.  Evidence that the reactivity of the martian soil is due to superoxide ions. , 2000, Science.

[14]  S. Read,et al.  Excitation functions for A ⩾ 6 fragments formed in 1H- and 4He-induced reactions on light nuclei , 1984 .

[15]  W. Banerdt,et al.  Mars: The regolith-atmosphere-cap system and climate change , 1982 .

[16]  R. Reedy.  Nuclide production by primary cosmic‐ray protons , 1987 .