PROTECTIVE ROLE OF MARTIAN ANALOGUE MINERALS FOR BIOMOLECULES AGAINST RADIATION EFFECTS

Organic compounds that form in space have been delivered over time to Mars and other planets via meteorites, comets, and interplanetary dust particles (IDPs). The fate of organic material on the surface of Mars and other planets must be affected by the environment, such as presence of highly oxidant species. Organic material delivered to these planets is also subject to effects of UV radiation, ionizing gamma radiaton and highly energetic cosmic rays and particles. Penetration depth of UV radiation into soils is only in the sub-millimeter to millimeter range and depends on the properties of the soil, such as particle size. Gamma rays, on the other hand, have significantly higher energy range: > 2 x 10^-14 Joule, compared to energy of UV radiation: 5 x 10^-19 to 2 x 10^-17 Joule. John Bernal of England had proposed that minerals may have protected organic molecules from effects of ionizing radiation by adsorbing them on their surfaces. He had also suggested that minerals may have served as catalyst for the formation of large biomolecules by orienting them on their surfaces in a favorable position for reactions to occur. We have investigated the protective effect of minerals for biomolecules against the effect of UV radiation. 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. We also demonstrated that 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, the same organic compounds completely decomposed upon mixing with iron oxide (Fe₂O₃) before UV irradiation. We continued our research employing extended irradiation times and higher gamma doses on the same mineral-organic mixtures: Gamma radiation from a Co-60 source was used for the irradiation. The dose of irradiation corresponded to 100,000 years and 500,000 years on Martian surface. Here we present the gamma irradiation results, the roles of presence of 1% perchlorate in the mineral-organic mixtures and atmospheric composition, i. e., comparison of results obtained by gamma irradiation performed in air and gamma irradiation in 98% CO₂atmosphere. 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.