The study of terrestrial fossils in ancient rocks: a crucial approach to identify potential signs of life on Mars

The NASA Perseverance rover is actively exploring Jezero Crater, analyzing igneous and sedimentary rocks from the crater floor and delta deposits. The rock samples that will be returned by the Mars Sample Return (MSR) mission in the 2030s will be subjected to detailed laboratory studies.

Some samples may contain traces of ancient Martian life, which are challenging to detect due to their morphological simplicity and subtle geochemical expressions. Using volcanic sediments from Kitty’s Gap Chert (Pilbara, Australia) of 3.45 billion years as analogues, researchers detail the steps needed to demonstrate their syngenicity and biogenicity. Various analytical methods, including optical and electron microscopy, Raman spectroscopy, X-ray fluorescence spectroscopy, and mass spectrometry, have been employed at different scales. Sedimentological, petrological, mineralogical, and geochemical analyses document a coastal environment of deposition, consistent with the development of microbial life. Morphological, elemental, and molecular analyses of carbonaceous matter associated with potential fossil remnants reveal enrichment in bioessential trace metals (V, Cr, Fe, Co, etc.) and colocalized aromatic and aliphatic molecules of biological origin. This study illustrates the analytical protocol necessary to optimize the detection of fossil traces of life in Martian rocks.

This work is reported on the CNRS Chimie website

Reference
Multi-Technique Characterization of 3.45 Ga Microfossils on Earth: A Key Approach to Detect Possible Traces of Life in Returned Samples from Mars
Laura Clodoré, Frédéric Foucher, Keyron Hickman-Lewis, Stéphanie Sorieul, Jean Jouve, Matthieu Réfrégiers, Guillaume Collet, Stéphane Petoud, Bernard Gratuze, Frances Westall
Astrobiology 2024
http://doi.org/10.1089/ast.2023.0089

Raman spectroscopy for detecting biomolecules below surface of Mars

Chlorophyllin, beta-carotene, melanin, chitin, cellulose, naringenin and quercetin: these exotic-sounding compounds are biomolecules that allow certain organisms to live in extreme environments. They are thus prime targets for the search for life on Mars. In order to assess their resistance to Martian conditions, an experiment called BIOMEX, for BIOlogy and Mars EXperiment, was carried out on the exterioir of the International Space Station (ISS).

The molecules were mixed with Martian soil analogs before being exposed to solar radiation outside the ISS for 469 days. Back on Earth, they were   analyzed by Raman spectroscopy at the German Aerospace Center (DLR) in Berlin.

Raman spectroscopy analyses the molecular and mineralogical composition of a sample. Compatible with robotic space missions, it is one of the key techniques for searching for traces of life on Mars. NASA's Perseverance rover currently exploring Jezero Crater is equipped with two Raman spectrometers, and ESA's future ExoMars mission will also use one to aid detection of possible biosignatures on Mars in 2030.

The BIOMEX experiment involved many researchers, including members of the Exobiology team at CBM, Olréans. The results, published in the Science Advances, reveal that these biomolecules are resistant to Mars conditions because the minerals composing the Martian soil have a protective effect against UV. Most importantly, the study shows that these molecules could be identified without difficulty on Mars by Raman spectroscopy.

Biosignature stability in space enables their use for life detection on Mars
Mickael Baqué,Theresa Backhaus et al.
Science Advances, Vol 8 -DOI: 10.1126/sciadv.abn7412