Identification of Martian biota using their radioresistance ability and specific isotopic composition

Details Identification of Martian biota using their radioresistance ability and specific isotopic composition Identification of Martian biota using their radioresistance ability and specific isotopic composition

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....11784p&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #11784

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Scientific paper

Because of a thin atmosphere and weak magnetic field, Martian surface is a subject to high levels of ionizing radiation. On the other hand, variations in Martian obliquity produce the global climate oscillations (with the main period ~120000 years) of the great magnitude. Martian biota would accumulate large radiation dosage during the periods of cold climate, when it would be in the dormant state and would rebuild its population during the periods of warm climate. Therefore, all types of hypothetical Martian microorganisms living in subsurface layers of soil have to posses very high radiation tolerance. In our experiments, we find that "ordinary" bacteria (Escherichia coli and two species of Bacillus ) can develop radioresistance ability after a number of cycles of exposure to the high (almost lethal) radiation dosages, followed by recovery of the bacterial population. We show that natural cycles of this kind could take place only on Mars. On the other hand, high radiation tolerance is hardly necessary for the survival in any natural environment on Earth. A few number of terrestrial microorganisms (radioresistant bacteria) posses this peculiar ability (Deinococus radiodurance , Rubrobacter radiotolerance, Rubrobacter xylanophilus ). The radiation background on Earth, including vicinity of natural nuclear reactor Oklo is many orders of magnitude lower than the lethal dose for these microorganisms. We show that such radioresistance can be "trained" only in the Martian conditions. Therefore, we propose that Earth has been infected several times by the Martian biota on Martian meteorites. We propose that high radioresistance could be a strong sign of the Martian origin for potential microorganisms acquired in the sample return missions. Another way to identify "Martian" microorganisms and exclude contamination in returned samples involves analysis of the radionuclides abundance (being produced by the high energy cosmic rays in the Martian soil). We show that these radionuclides (3H, 14C, 32Si,41Ca) should have higher concentration in the hypothetical Martian microorganisms comparing to any terrestrial analogues. We propose a set of measurements of such "isotopic imprints" with accelerator mass spectrometry. We also show that unusually high ratios of stable isotopes 15N/14N and D/H in the Martian atmosphere can be used for identification of Martian microorganisms because those ratios would be incorporated into the Martian biota.

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