美国圣路易斯华盛顿大学
课题组进行了动力学实验，以确定卤氧物种氯酸盐和溴酸盐氧化类火星流体中溶解的Mn(II)的反应性。研究发现，在火星表面广泛分布的卤氧物种，其诱发的锰氧化速率比O2大得多。通过比较所有可用氧化剂(包括活性氧物种过氧化物和超氧化物)的潜在氧化率，研究人员认为卤氧物种是火星上最有可能的锰氧化剂。此外，实验沉淀出锰氧化物矿物，它在光谱上与火星上报道的深色锰积聚物相似。研究结果提供了在火星早期预期的地球化学条件下形成锰氧化物的可行途径，并表明这些阶段可能记录了一个活跃的卤素循环，而不是大量的大气氧化过程。
据悉，火星车在火星上现场调查发现，在盖尔陨石坑和奋进陨石坑，氧化锰是裂缝充填材料。先前的研究将这些矿物解释为早期火星大气氧气的指示器。相比之下，研究者认为锰被氧化的可能性极小，因为在类似火星条件下的反应动力及其缓慢，需要更活泼的氧化剂。
附：英文原文
Title: Formation of manganese oxides on early Mars due to active halogen cycling
Author: Mitra, Kaushik, Moreland, Eleanor L., Ledingham, Greg J., Catalano, Jeffrey G.
Issue&Volume: 2022-12-22
Abstract: In situ rover investigations on Mars have discovered manganese oxides as fracture-filling materials at Gale and Endeavour craters. Previous studies interpreted these minerals as indicators of atmospheric oxygen on early Mars. By contrast, we propose that the oxidation of manganese by oxygen is highly unlikely because of exceedingly slow reaction kinetics under Mars-like conditions and therefore requires more reactive oxidants. Here we conduct kinetic experiments to determine the reactivity of the oxyhalogen species chlorate and bromate for oxidizing dissolved Mn(II) in Mars-like fluids. We find that oxyhalogen species, which are widespread on the surface of Mars, induce substantially greater manganese oxidation rates than O2. From comparisons of the potential oxidation rates of all available oxidants (including reactive oxygen species peroxide and superoxide), we suggest that the oxyhalogen species are the most plausible manganese oxidants on Mars. In addition, our experiments precipitated the manganese oxide mineral nsutite, which is spectrally similar to the dark manganese accumulations reported on Mars. Our results provide a feasible pathway to form manganese oxides under expected geochemical conditions on early Mars and suggest that these phases may record an active halogen cycle rather than substantial atmospheric oxygenation.
DOI: 10.1038/s41561-022-01094-y
Source: https://www.nature.com/articles/s41561-022-01094-y