Shielding biomolecules from effects of radiation by Mars analogue minerals and soils

• Published in: International journal of astrobiology 2017-07, Vol.16 (3), p.280-285
• Main Authors: Ertem, G., Ertem, M. C., McKay, C. P., Hazen, R. M.
• Format: Article
• Language: English
• Subjects: Anhydrite; Astrobiology; Atmospheric particulates; Biomolecules; Calcite; Calcium; Calcium carbonate; Calcium carbonates; Calcium sulfate; Calcium sulphates; Carbonates; Clay; Clay minerals; Clay soils; Comets; Decomposition; Dust storms; Earth; Exploration; Exposure; Extraterrestrial life; Gamma radiation; Gamma rays; Ionizing radiation; Iron; Iron oxides; Irradiation; Kaolinite; Laboratories; Mars; Mars dust effects on solar radiation; Mars soil; Mars surface; Meteors & meteorites; Minerals; Organic compounds; Particle size; Penetration depth; Photolysis; Prebiotics; Purines; Pyrimidines; Radiation effects; Radiation shielding; Science; Soil; Soil properties; Soils; Space missions; Ultraviolet radiation; Uracil; γ Radiation
• ISSN: 1473-5504; 1475-3006
• DOI: 10.1017/S1473550416000331

Organic compounds have been delivered over time to Mars via meteorites, comets and interplanetary dust particles. The fate of organic material on the surface of Mars must be affected by the Martian environment, in particular by ultraviolet (UV) and other ionizing radiation. Penetration depth of UV radiation into soils is in the sub-millimetre to millimetre range and depends on the properties of the soil. The aim of this research is to study the possible protective role of Martian analogue minerals and soils for survivability of biomolecules against UV radiation and to compare their decomposition rates within a 1 mm-thick portion of the surface. Results demonstrated that minerals offer significant protection to biomolecules purine, pyrimidine and uracil against UV photolysis. In the absence of these minerals, organic compounds are completely degraded when subjected directly to UV photolysis equivalent to only 5 Martian day's exposure. However, similar UV exposure of organics dried from solution onto powdered calcium carbonate (calcite; CaCO3), calcium sulphate (anhydrite; CaSO4), clay-bearing Atacama dessert soil and 7 Å clay mineral kaolinite [Al2Si2O5(OH)4] results in only 1–2% loss of organics. Mixtures of purine and uracil with calcium carbonate exposed to gamma radiation of 3 Gy (3 Gray), which corresponds to approximately 15 000 days on Mars, results in up to 10% loss of organics. By contrast, these organic compounds completely decomposed upon mixing with iron oxide (Fe2O3) before UV irradiation. As the search for extinct or extant life on Mars has been identified as a goal of top priority in NASA's Mars Exploration Program and continues with several missions planned to the red planet by both NASA and the European Space Agency (ESA) in the next few decades, our findings may play a useful role in identifying optimal target sites on the Martian surface for future missions.