Abstract EANA2024-58

While evidence of the existence of organic molecules on Mars has already been showed, their detection and identification remain challenging due to several factors that can influence their preservation and detectability. In order to improve this, most of the recent Martian missions are equipped with Near Infrared (NIR) vibrational spectroscopy (1). However, the large variety of environmental factors and the interactions between the molecule and the mineral, may turn the interpretation of the IR spectral data very complicated (2). In addition, the thin Martian atmosphere allows ionizing radiations (e.g. UV radiation) to reach the surface, compromising the stability of organic compounds. At the surface, preservation of organic compounds may be obtained thanks to the presence of photoprotective minerals (3). To maximize the probabilities to detect organic compounds on Mars, it is crucial to study the effect of UV radiation of organics adsorbed in minerals that can be representative of Martian soils. In this work, L-histidine adsorbed at different pHs on Nontronite is studied by infrared spectroscopy in order to contribute to the identification of amino acids in Martian missions that make use of this spectroscopic technique. In addition, the UV radiation degradations for the pure amino acid and adsorbed onto Nontronite at different pHs are studied in order to suggest the best preservation environments for its identification on Mars. The adsorption was performed by mixing the nontronite powder with aqueous solutions of L-histidine at different pH conditions. The suspensions were kept under rotation on a test-tube rotator for 24 hours, using an equilibrium adsorption method as previously described by Fornaro et al. (2).  Finally, the samples were dried at 30 ◦C in an oven. The interactions between the L-histdine and nontronite was assessed using a Bruker VERTEX 70v FTIR interferometer (Diffuse Reflectance InfraRed Fourier Transform Spectroscopy, DRIFTS) while the molecular stability was performed coupling the VERTEX 70v with a Newport Xenon enhanced UV lamp allowing us to follow the molecular kinetic degradation.

References: (1) Vago, J. L. et al. (2017) Astrobiology, 17, 471–510. (2) Fornaro, T. et al. (2020) Front. Astron. Space Sci., 7, 539289. (3) Fornaro, T. et al. (2018) Life 8 (4), 56.