Manganese oxidation as a relevant process for the astrobiological exploration on Mars

• Ano de defesa: 2024
• Autor(a) principal: Salgado, Willian Pinheiro
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Astrobiologia; Astrobiology; Manganês; Manganese; Mars; Marte; Oxidação; Oxidation
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/46/46136/tde-22052025-100014/

Fundamental questions exist about the nature and history of redox processes operating on the Martian surface environment. The planet\'s surface is full of minerals that could provide clues about the planet\'s past characteristics and evolution. NASA\'s Curiosity, Opportunity and Perseverance rovers have found deposits of manganese (Mn) oxides and hydroxides in Gale, Endeavor, and Jezero craters on Mars. These minerals are formed through the reaction between Mn(II) in an aqueous solution and a high-potential oxidizing agent, and may provide unique information about the Martian paleoenvironment, recording past pH conditions, redox potential, and interaction between rocks and liquid water. While in the terrestrial environment, Mn(II) oxidation is thought to be primarily a consequence of biological activity, we conducted laboratory simulations to investigate the capacity of oxyhalogen species — perchlorate ClO4-(aq), chlorate ClO3-(aq), and bromate BrO3-(aq) ions — as Mn(II) oxidants in an abiotic Martian setting. Bromate oxidizes Mn(II) under acidic conditions, where oxidation by other oxidants, such as O2 or reactive oxygen species (ROS), cannot occur because of unfavorable thermodynamics. Hence, the presence of oxidized Mn minerals on Mars may suggest the occurrence of a halogen cycling on Mars, in contrast to a past O2-rich atmosphere. The samples were analyzed using a multi-technique approach, combining data from XRD, Raman spectroscopy, XANES and SEM-EDS. The phase determination of the samples was inconclusive, however the results suggest the formation of Mn(IV) or a mix Mn(III/IV) (hydr)oxides, with a low Point of Zero Charge value (PZC = 2.61). Mn oxidized minerals found on Mars offer a valuable tool for assessing its habitability potential. We suggest these Mn minerals are key samples for future Mars sample return missions to Earth.