Characterization of microbial biosignatures in taphonomic experiments in preparation for the ESA Exomars mission

Abstract

A multidisciplinary science, astrobiology requires a sum of in-depth knowledge to drive a constant quest concerning the comprehension of life here and elsewhere. Beyond philosophical debates about its meaning, life represents organisms from all shapes and size, cells, molecules which leave traces, where they were active and, in particular, where they stopped to be. When it is about knowing which form of life was at a specific place, or if this life ever existed in this environment, a test battery has to be set in motion to determinate its origin. On Mars or on Earth, numerous challenges block the way to this biosignature determination. The morphological and chemical analyses are the minimum that are demanded to have a realistic idea about what is under the microscope. In the framework of the ESA Exomars mission and the search for life on Mars, this study had the objective to characterize fossil biosignatures following a fossilization simulation to extract exploitable traits for future Martian rock sample analysis. The process used during this experiment in several steps was to heat cyanobacteria (4 strains with distinct morphologies) and clay (kaolinite and montmorillonite K10 in separated samples) mixtures at 90°C for 48 hours and 1 week in two isolated experiments. After this heating period, samples were analyzed with microscopes, FTIR microspectroscopy and Raman microspectroscopy. These analyses were done in Earth lab conditions. In order to simulate the Exomars mission conditions, an additional series of Raman analyses were carried out on the same material, configuring the instrument with the data from RLS, a tool which will be on the Exomars rover Rosalind Franklin. Further to these analyses, morphologic and chemical biosignatures were detected in variable proportions according to the cyanobacteria strains, and the various tested conditions. Despite the meagre results for the RLS simulation, the experimental procedure is able to detect traces of life preserved in the fossilization simulation.