The photochemical evolution of meteoritic polycyclic aromatic hydrocarbons in clay environments on prebiotic Earth and Mars

Abstract

<p>Polycyclic aromatic hydrocarbons (PAHs) represent ~20% of cosmically available carbon [1, 2]. The further photochemical evolution of PAHs on planetary surfaces is of interest to early Earth origin-of-life studies and Mars origin-of-life speculations. Much of the literature has focused on small molecules contained in meteorites, such as amino acids and nucleic acid bases, and their potential as a carbon source for prebiotic chemistry on early Earth. However, 75% of extraterrestrial organic matter in meteorites is in aromatic form [3], and is more likely to survive the journey to a planetary surface, during which much of the small molecules can be destroyed. These stable carbon compounds could later be broken down into smaller, more biologically relevant molecules by photocatalysis on clay mineral surfaces in the ultraviolet radiation regime of early Earth and Mars.</p> <p>Here we experimentally test whether PAHs degrade when adsorbed to nontronite clay and exposed to ultraviolet radiation. Experiments were performed at the INAF Observatory of Arcetri and in the PALLAS chamber at Utrecht University and were monitored with <em>in-situ</em> diffuse reflectance infrared spectrometry (DRIFTS) measurements. PAHs and any degradation products were extracted post-irradiation and analyzed with nuclear magnetic resonance (NMR).</p> <p>[1] Allamandola, L. J., Tielens, A. G. G. M., & Barker, J. R. (1989). <em>The Astrophysical Journal Supplement Series</em>, <em>71</em>, 733-775.</p> <p>[2] Puget, J. L., & Léger, A. (1989). <em>Annual review of astronomy and astrophysics</em>, <em>27</em>(1), 161-198.</p> <p>[3] Sephton, M. A. (2002). <em>Natural product reports</em>, <em>19</em>(3), 292-311.</p>