Sterilization of Martian surface by cosmic radiation

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 x 10(6) yr and below this level by the long-lived radioactivity in about 4 x 10(7) yr. Destructive influence of cosmic radiation could also significantly change the mean atomic mass of hypothetical Martian fossil macromolecules and C-13/C-12 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. (C) 2002 Elsevier Science Ltd. All rights reserved.