Detection of biosignatures on Mars using Raman spectroscopy: expectations and limits

Kurzfassung

The well-established presence of liquid water on the surface of Mars during the Noachian and early Hesperian periods signifies that the planet was partly habitable [1,2]. Liquid water disappeared from the surface of Mars ca. 3.5 billion years ago [2]. Nevertheless, contrary to the Early Earth, which was covered by a global ocean, Mars was probably only patchily covered by lakes or seas, not necessary connected to each other. Consequently, life may have appeared and disappeared on one, or several, place(s) without colonizing the whole planet; hence the concept of punctuated spatial and temporal habitability proposed by Westall et al (2015) [2]. In addition to making landing site selection crucial, this specificity of Mars could have limited the evolution of life to very simple microorganisms. Lack of oxygen in the atmosphere and, therefore, of an ozone layer, meant that its surface has been continuously exposed to high-energy UV radiation (down to 190 nm wavelength), deleterious for organics and responsible for the formation of hydrogen peroxide [1,3]. In the absence of a magnetic field, it is also exposed to the solar and galactic cosmic rays that reach the surface and the near subsurface [4]. In addition to making the surface of Mars presently highly inhospitable, this radiative environment may have altered inorganic and organic biosignatures with time. Here we present the results of experiments to study the preservation of different types of representative biosignatures and their detectability using Raman spectroscopy under Mars conditions. This method, able to analyse both organic and mineral phases and compatible with in situ exploration, is particularly relevant to search for past or present traces of life and equipped the current NASA Mars 2020 and future ESA ExoMars rovers. For ancient traces of life, we used terrestrial Precambrian microfossils as a reference. We showed that their biogenecity is difficult to demonstrate unambiguously using Raman spectroscopy alone and that such traces of life would be probably too subtle to be detected in situ on Mars [5,6]. For recent traces of life, where biomolecules have not been transformed into kerogen with time and metamorphism, we performed experiments in the laboratories where we studied the degradation of the Raman signal of different pigments and molecules during UV and cosmic rays irradiation. In particular, an original Raman system, called RAMSESS (RAMan SpEctroscopy for in Situ Studies), was developed at CNRS CEMHTI-Pelletron, Orléans, France, to study the changes in the Raman signal of different minerals and organic molecules in situ within the irradiation chamber (see Fig. 1) [7]. These experiments are very complementary to those obtained during the BIOMEX experiment on-board the ISS [8,9]. [1] J.-P. Bibring, Y. Langevin, J. F. Mustard, F. Poulet, R. Arvidson, A. Gendrin, B. Gondet, N. Mangold, P. Pinet, F. Forget and the OMEGA team, Science, 312, 400 (2006). [2] F. Westall, F. Foucher, N. Bost, M. Bertrand, D. Loizeau, J. L. Vago, G. Kminek, F. Gaboyer, K. A. Campbell, J.-G. Bréhéret, P. Gautret and C. S. Cockell, Astrobiology, 15, 998 (2015). [3] M. A. Bullock, C. R. Stoker, C. P. McKay and A. P. Zent, Icarus, 107, 142 (1994). [4] G. de Angelis, M. S. Clowdsley, R. C. Singleterry and J. W. Wilson, Advances in Space Research, 34, 1328 (2004). [5] F. Foucher and F. Westall, Astrobiology, 13:1, 57 (2013). [6] F. Foucher, M. R. Ammar and F. Westall, Journal of Raman Spectroscopy, 46, 873 (2015). [7] A. Canizarès, F. Foucher, M. Baqué, J.-P. de Vera, T. Sauvage, O. Wendling, A. Bellamy, P. Sigot, T. Georgelin, P. Simon and F. Westall, Applied Spectroscopy, 76, 723 (2022). [8] J.-P. de Vera, M. Alawi, T. Backhaus, M. Baqué, D. Billi, U. Böttger, T. Berger, M. Bohmeier, C. Cockell, R. Demets, R. de la Torre Noetzel, H. Edwards, A. Elsaesser, C. Fagliarone, A. Fiedler, B. Foing, F. Foucher, J. Fritz, F. Hanke, T. Herzog, G. Horneck, H.-W. Hübers, B. Huwe, J. Joshi, N. Kozyrovska, M. Kruchten, P. Lasch, N. Lee, S. Leuko, T. Leya, A. Lorek, J. Martinez-Frias, J. Meessen, S. Moritz, R. Moeller, K. Olsson-Francis, S. Onofri, S. Ott, C. Pacelli, O. Podolich, E. Rabbow, G. Reitz, P. Rettberg, O. Reva, L. Rothschild, L. G. Sancho, D. Schulze-Makuch, L. Selbmann, P. Serrano, U. Szewzyk, C. Verseux, J. Wadsworth, D. Wagner, F. Westall, D. Wolter and L., Zucconi, Astrobiology, 19:2, 145 (2019). [9] M. Baqué, T. Backhaus, J. Meeßen, F. Hanke, U. Böttger, N. Ramkissoon, K. Olsson-Francis, M. Baumgärtner, D. Billi, A. Cassaro, R. de la Torre Noetzel, R. Demets, H. Edwards, P. Ehrenfreund, A. Elsaesser, B. Foing, F. Foucher, B. Huwe, J. Joshi, N. Kozyrovska, P. Lasch, N. Lee, S. Leuko, S. Onofri, S. Ott, C. Pacelli, E. Rabbow, L. Rothschild, D. Schulze-Makuch, L. Selbmann, P. Serrano, U. Szewzyk, C. Verseux, D. Wagner, F. Westall, L. Zucconi and J.-P. P. de Vera., Science Advances, 8, 7412 (2022)