Ultraviolet Photoprocessing of Glycine Adsorbed on Various Space-Relevant Minerals

Giovanni Poggiali,John Robert Brucato,Maria Angela Corazzi,Simone Potenti,Teresa Fornaro

doi:10.3389/fspas.2020.00018

Abstract

Mineral surfaces are energetic environments that can assist prebiotic organization by adsorbing selected molecules and allowing their concentration and chemical evolution, possibly toward complex (pre)biological systems. This dynamic rocky environment can also play a crucial role as promoters of chemical reactions towards increasing molecular complexity. Moreover, presence of minerals can mediate the effects of electromagnetic radiation and influence the photostability of biomolecules, catalyzing photoreaction or protecting molecules against degradation. Such interactions are responsible for the preservation/degradation mechanisms of organic molecules in space. In particular, the discovery of organic molecules on asteroids and comets confirms their role as transport and delivery vehicles of building blocks of life on Earth and possibly on other bodies of the Solar System, and the study of this kind of processes can improve our knowledge in astrobiology.Many different prebiotic and bio-molecules were detected in space and in meteorites, but among them amino acid glycine (H2NCH2COOH), is one of the most important. It is the simplest of the 20 biogenic amino acids and it is conceivably the link between complex organic molecules detected in our evolved Solar System and prebiotic molecules observed in the interstellar medium and protostellar environment. Laboratory simulations of UV processing may provide key insights into the survival of glycine and other biomarker in space environment, which is of particular relevance for upcoming space exploration missions on planetary surfaces, like ESA-Roscosmos ExoMars 2020, and sample return missions, like NASA OSIRIS-REx.We report a laboratory study of UV irradiation of glycine adsorbed on various space relevant minerals, i.e. forsterite, antigorite, spinel and pyrite, using a calibrated enhanced UV Xenon lamp, which demonstrated good performance as solar simulator. Comparing protective/catalytic effects of various minerals helps to unravel the role of rocky surfaces in the origin of life and provides hints for the search of organics in present and future robotic space exploration missions.

Highlights

Interactions at the interfaces between minerals and prebiotic molecules and their role in the origin of life are some of the most discussed topics in astrobiology (Bernal, 1951; Luther et al, 1998; Ertem, 2004; Hazen and Sverjensky, 2010; Lambert et al, 2017)
An example of how spectral features can change before and after GLY adsorption is reported in Figure 3 for pyrite, where spectra of pure GLY, pure pyrite, and GLY adsorbed on pyrite are shown
In our work we analyzed the UV irradiation of pure GLY and adsorbed on space-relevant minerals that are abundant in a wide range of environments across the Solar System: the serpentine antigorite, olivine forsterite, oxide mineral spinel, and iron– sulfide mineral pyrite

Summary

Introduction

Interactions at the interfaces between minerals and prebiotic molecules and their role in the origin of life are some of the most discussed topics in astrobiology (Bernal, 1951; Luther et al, 1998; Ertem, 2004; Hazen and Sverjensky, 2010; Lambert et al, 2017). Even before the formation of the rocky surfaces of planets, asteroids, and other minor bodies, mineral surfaces of dust grains in the interstellar medium may promote the synthesis of complex molecules (Brucato et al, 2006). The results reported in this work show that a few hours of exposure to UV may transform organic molecules during their absorption phase on a mineral substrate, and if subsequent deposition of a shielding material occurs, such as dust grains or ices accumulating in deep space or sediments on a planet, these molecules would be preserved in an altered state. Studies on photoprocessing and survivability of prebiotic molecules on rocky surfaces are fundamental both to understand their role in the origin of life and to estimate the likelihood of preservation of possible biomarkers that might be detected in such conditions by space missions

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