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Understanding the past habitable environments of Mars increases the requirement to recognize and examine modern analogs and to evaluate the mechanisms that may preserve biosignatures in them. The phenomenon that originates and preserves possible microbial biosignatures in mineral phases is of particular interest in astrobiology. On Earth, the precipitation of carbonate matrices can be mediated by bacteria. Besides microbialites and other sedimentary structures, carbonate formations can be observed in certain karstic caves. The present work is focused on the remote laser-induced breakdown spectroscopy (LIBS) characterization of cyanobacteria, exploring the possibilities for identification and discrimination on carbonate substrates. For this purpose, the extremophile cyanobacterium Chroococcidiopsis sp. (collected from the Nerja Cave, Malaga, Spain) was analyzed under laboratory-simulated martian conditions in terms of chemical composition and gas pressure. LIBS results related to acquired molecular emission features allowed bacterial differentiation from the colonized mineral substrate. In addition, the limits of detection were estimated with a laboratory-grown culture of the cyanobacterium Microcystis aureginosa. Our results reveal LIBS's capability to detect biological traces under simulated martian conditions. Additionally, the time-resolved analysis of the biological samples demonstrates the selection of optimal temporal conditions as a critical parameter for the preferential acquisition of molecular species in organic material. [ABSTRACT FROM AUTHOR]

Detection of indigenous organic matter (IOM) in rocks using molecular-laser-induced breakdown spectroscopy (LIBS) is reported. IOM refers to carbon-based compounds of variable complexity intimately associated with mineral and amorphous phases both in condensed phases and in a dispersed state spatially associated to mineral aggregates. The presence of IOM may provide valuable information in astrobiology about the possibility of past or present life on planetary bodies. Kerogen, charcoal, bitumen, and graphite are only some examples of IOM that may appear in rocks. This paper reports the detection of kerogen in oil shale (a sedimentary rock also containing dolomite, calcite, pyrite, quartz, and albite) from the LIBS study of CN and C 2 emissions under simulated Martian conditions. A set of oil shale samples with variable concentrations of total organic carbon (TOC) ranging from 2.78% to 12.74% were analyzed. A careful LIBS analysis of molecular species associated within hydrocarbons confirmed the presence of organic matter derived from kerogen. A linear correlation between the CN and C 2 emissions and the %TOC was observed. Using a simulated Martian atmosphere as surrounding gas, the limit of detection for organic matter was calculated in 0.42% TOC. Additionally, the potential interferences in geological samples for LIBS detection of molecular species were also evaluated. Results demonstrate that common elements in rocks such as Ca, Fe, K, Mg, Na and Si do not interfere with the detection of organics. In contrast, Ti at concentrations above 0.4% may induce false positive results using the CN emission at 388.34 nm. To overcome this inconvenience, the CN emission at 387.14 nm may be used which, although less sensitive, is free from titanium interference. [Display omitted] • LIBS novel detection of native organic matter through molecular emission recognition in complex sedimentary rocks. • Contribution of different carbon sources to the collected emission signal under Martian conditions. • Possible interferences in LIBS molecular detection of CN and C 2 species. • Linear correlation between intensity of CN and C 2 molecular systems and TOC content. • LIBS analysis for geological and astrobiological applications. [ABSTRACT FROM AUTHOR]