Raman spectroscopy and the search for life signatures in the ExoMars Mission

Abstract

The survival strategies of extremophilic organisms in terrestrially stressed locations and habitats are critically dependent on the production of protective chemicals in response to desiccation, low wavelength radiation insolation, temperature and the availability of nutrients. The adaptation of life to these harsh prevailing conditions involves the control of the substratal geology; the interaction between the rock and the organisms is critical and the biological modification of the geological matrix plays a very significant role in the overall survival strategy. Identification of these biological and biogeological chemical molecular signatures in the geological record is necessary for the recognition of the presence of extinct or extant life in terrestrial and extraterrestrial scenarios. Raman spectroscopic techniques have been identified as valuable instrumentation for the detection of life extra-terrestrially because of the use of non-invasive laser-based excitation of organic and inorganic molecules, and molecular ions with high discrimination characteristics; the interactions effected between biological organisms and their environments are detectable through the molecular entities produced at the interfaces, for which the vibrational spectroscopic band signatures are unique. A very important attribute of Raman spectroscopy is the acquisition of molecular experimental data non-destructively without the need for chemical or mechanical pre-treatment of the specimen; this has been a major factor in the proposal for the adoption of Raman instrumentation on robotic landers and rovers for planetary exploration, particularly for the forthcoming European Space Agency (ESA)/National Aeronautics and Space Administration (NASA) ExoMars mission. In this paper, the merits of using Raman spectroscopy for the recognition of key molecular biosignatures from several terrestrial extremophile specimens will be illustrated.

Potential for analysis of carbonaceous matter on Mars using Raman spectroscopy

“…Existing literature on the application of Raman spectroscopy to the search for evidence of life has focussed on the detection of complex organic compounds, such as pigments in suitable geological matrices (Edwards et al, 2012;Vítek et al, 2009aVítek et al, , 2009b. The selection of appropriate biomarkers in the geological record is currently the subject of investigation by various groups (e.g.…”

Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method

“…The detection of biomarkers, molecules that cannot be synthesised in large quantities by abiogenic means (Eglinton et al 1964 ), is a priority for the ESA ExoMars mission in 2018. A Raman spectrometer equipped with a 532 nm laser (Edwards et al 2012a ) will be among the suite of instruments on board to aid the detection process (Edwards et al 2012b ). This excitation wavelength was chosen for the range of molecular targets that could be acquired, while reducing background fluorescence and being able to equip the rover with a commercially available laser that would meet the mission mass and power requirements (Edwards et al 2012a ).…”

Raman Spectroscopic Techniques for Planetary Exploration: Detecting Microorganisms through Minerals

“…RS is a nondestructive technique for the identification of organic and inorganic compounds based on molecular vibrations and can be used for detection of life in planetary exploration ( Jorge Villar and Edwards, 2006). Both the European Space Agency and the National Aeronautics and Space Administration have assigned a Raman instrument to one of their scheduled Mars missions, ExoMars in 2018 with 532 nm excitation (Edwards et al, 2012) and Mars 2020 (Beegle et al, 2014), respectively. NASA will equip their rover with two Raman instruments: one for the SHERLOC system with 248.6 nm excitation and one for the SuperCam system with 532 nm excitation and gated detection that can be used for stand-off measurements .…”

“…On Earth, various strategies have evolved over time to allow for survival under extreme conditions, for instance, physical protection via mobilization or transformation of minerals (Edwards et al, 1997;Jorge Villar et al, 2005) or hiding in and on different minerals (epiliths), inside porous rocks (endoliths), or inside cracked rocks (chasmoliths) (Edwards, 2010). Chemical protection against ultraviolet radiation is offered by compounds such as scytonemin or carotenoids (Edwards et al, 2012). To prevent desiccation, organisms may have high concentrations of organic osmotic solutes like glycerol, simple sugars, amino acids in their cytoplasm or use extracellular oxalate precipitates (Böttger et al, 2013).…”