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Paper: Dinitrogen as a Possible Biomarker for Exobiology: The Case of Titan
Volume: 213, Bioastronomy '99: A New Era in Bioastronomy
Page: 333
Authors: Simakov, Michael
Abstract: Nitrogen is an essential element for life. There are only two bodies in our Solar System which have a large amount of gaseous dinitrogen in their atmospheres - Earth and Titan, the largest moon of Saturn. On Earth the biological nitrogen cycle is responsible for the presence of dinitrogen in the atmosphere. Despite of initial form of nitrogen (dinitrogen or ammonia) in primordial atmosphere, it is converted to other forms by several effective processes through time of planetary development. These reactions resulted in fixing almost all nitrogen at the end stage of accretion or early stage of planetary evolution. The fixed nitrogen could have been a significant source of energy for the earliest biosphere. It is possible that only living or near living (protobiont) systems could support high concentration of dinitrogen in the atmosphere. Therefore, the first candidate for possible exobiology activity is Titan with its dense nitrogen atmosphere. The protobiont- like systems on Titan may have chemolithoautotrophical nature and use a reaction of nitrate reduction as source of energy. Electron donors that may be important for such systems include Fe (II), pyrite and organic material. The most appropriate sites for such activity are: (1) the upper layers of internal water ocean when a cycle of freezing - thawing can generate electric potentials and accelerate the reactions; (2) the sites of cryogenic volcanism; (3) liquid water pools on the surface originated from meteoritic strikes. Some possible protobiont-like structures and mechanisms which could be responsible for evaluating of gaseous dinitrogen together with approaches for determining of such biological or prebiological activity on other planets outside of our Solar System will be discussed.
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