Detectability and discrimination of biomarker organic precursors in a low pressure CO2 atmosphere by LIBS

Abstract

In view of the new challenges that can arise in the next interplanetary missions, studies aimed at shedding light on the interpretation of acquired analytical signals are of high priority in planetary science. Among the suite of techniques used in this field, LIBS has gained ample acceptance after its successful demonstration in the Mars Science Laboratory rover. As a consequence, several planned missions to Mars integrate this technology due to its capability for the quantitative analysis of rocks, minerals, and soils. While LIBS is primarily an atomic spectroscopy tool, recent research has demonstrated that significant information concerning organic radicals in the plasma can be useful for identification of molecular solids such as polycyclic aromatic hydrocarbons. This work explores this application by studying atomic and molecular species generated in reactions within the plasma plume in a low pressure CO₂ atmosphere of selected organic compounds of interest as possible chemical biosignatures – adenine, glycine, pyrene and urea. The study also involves mixtures of variable composition of the organic compounds with carbonate salts, a material that has been detected in the surroundings of the landing site of the Perseverance rover of the upcoming Mars 2020 mission. Important routes for the formation of C₂ and CN radicals such as aromatic ring fragmentation and displacement reactions in the CO₂ atmosphere are identified using correlation analysis of the signals associated with the several emitting species detected in the plasma. The notion that LIBS can complement organic analysis techniques is further developed with successful data for differentiation between the organic compounds, with limits of detection from 3 wt% to 14 wt% in the carbonate matrix.