Alteration of biosignatures in a simulated Martian environment studied by Raman spectroscopy

Kurzfassung

Raman spectroscopy, sensitive to organic and mineral phases, is particularly suitable for the detection of biosignatures and therefore extremely useful in the context of current and future missions to Mars (Mars 2020, ExoMars and Mars Sample Return) [1,2]. It is particularly sensitive to pigments, such as carotenoids [3,4], and to kerogen (insoluble carbonaceous matter of biological origin) [5,6]. However, metamorphism and irradiation can alter these biosignatures over time. In the absence of plate tectonics, metamorphism on Mars would have remained limited (apart from impact metamorphism) but could have been sufficient to alter organic compounds. In addition, the surface of Mars has been continuously exposed to high-energy UV radiation, solar particles, and galactic cosmic rays, which may also have altered organic molecules near the subsurface [7-10]. ESA's ExoMars mission is equipped with a drill to take samples up to 2 m deep for this reason [11]. In this study, we first evaluate the effect of metamorphism on the Raman signal of microfossils by studying the evolution of the kerogen spectrum with temperature. Then, in order to evaluate the effect of particle irradiation on the Raman signal of biosignatures, we irradiated beta-carotene and microfossils using the Pelletron ion accelerator at the CEMHTI laboratory, CNRS, Orléans, France. In addition to ex situ high-resolution Raman spectroscopy imaging, we also used the RAMSESS 2 device (for RAMan SpEctroscopy for in Situ Studies 2), allowing us to study the variations of the Raman signal in situ in the irradiation chamber [9-10]. These experiments allowed us to estimate the alteration of the Raman signal of biosignatures studied in the near subsurface of Mars over time, up to several billion years [9-10]. This study was carried out with the support of CNES and the EMIR&A network. [1] F. Rull, Astrobiology ,17:6-7, 627 (2017) [2] K. A. Farley et al., Space Sci. Rev., 216:8, 142 (2020) [3] M. Baqué M. et al., Origin Life Evol. Bios., 46, 289 (2016) [4] P. Vitek et al., Astrobiology, 12:12, 1095 (2012) [5] F. Foucher et al., J. Raman Spec., 46, 873 (2015) [6] F. Foucher and F. Westall F., Astrobiology, 13:9, 887 (2013) [7] M. A. Bullock et al. (1994) Icarus, 107, 142 (1994) [8] G. D. Angelis et al., Adv. Space Res., 34, 1328 (2004) [9] F. Foucher et al., Icarus, 441, 116674 (2025) [10] L. Bourmancé et al., Int. J. Astro., in press (2025) [11] J. Vago et al., Astrobiology, 17 :6-7, 471 (2017)