ABSTRACT
The detection and identification of biomarkers as unambiguous indicators of past and present life in extraterrestrial scenarios from their Raman spectral signatures are reviewed, and our knowledge of key biomolecular compounds from terrestrial analogue sites of relevance to Martian exploration is surveyed. Raman spectrometers will form an essential part of the analytical protocols for both the NASA and ESA Roscosmos Mars missions scheduled for launch in 2020 with a specific “search for life” directive, which has not really been advanced since the Viking experiments of 1976: hitherto, much exploratory work has been carried out to identify the geological environments and the presence of subsurface water and crystalline hydrates at various selected landing sites. The challenges posed for the adoption of Raman spectroscopic techniques to definitively characterize biomolecular signals emanating from the remote analytical interrogation of the Martian surface and subsurface are considered from experience gained in assessing the adaptation processes, which are generated by terrestrial extremophilic colonies located in hostile environments on Earth: the strategies adopted by cyanobacteria to combat excessively high and low temperatures, desiccation, low nutrient supplies, harsh low-wavelength ultraviolet radiation insolation, and the influx of chemical toxins give a particularly good insight into what signatures can be expected from extant or extinct life on Mars and favored geological niches that are being exploited for the successful adaptation of the host matrix for its survival. Some key spectral biosignatures are presented and indication given of their recognition and presence in an extraterrestrial context for the first Raman analyses expected from Mars.
