Searching for Life on Mars: Selection of Molecular

The European Space Agency’s ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pas-teur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect spe-cific organic molecules or classes of molecules. Therefore, it is necessary to define and pri-oritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) or-ganic matter, and contamination. Once organic molecules are detected on Mars, further in-formation is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from un-expected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil bio-markers, but sequential extraction would be required to optimize the analysis of each of thes