1 Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London , London, UK.
2 Impacts and Astromaterials Research Centre, Department of Mineralogy, Natural History Museum , London, UK.
Astrobiology. 2018 Apr;18(4):454-464. doi: 10.1089/ast.2017.1717. Epub 2018 Jan 3.
Jarosite on Mars is of significant geological and astrobiological interest, as it forms in acidic aqueous conditions that are potentially habitable for acidophilic organisms. Jarosite can provide environmental context and may host organic matter. The most common extraction technique used to search for organic compounds on the surface of Mars is pyrolysis. However, thermal decomposition of jarosite releases oxygen into pyrolysis ovens, which degrades organic signals. Jarosite has a close association with the iron oxyhydroxide goethite in many depositional/diagenetic environments. Hematite can form by dehydration of goethite or directly from jarosite under certain aqueous conditions. Goethite and hematite are significantly more amenable than jarosite for pyrolysis experiments employed to search for organic matter. Analysis of the mineralogy and organic chemistry of samples from a natural acidic stream revealed a diverse response for organic compounds during pyrolysis of goethite-rich layers but a poor response for jarosite-rich or mixed jarosite-goethite samples. Goethite units that are associated with jarosite, but do not contain jarosite themselves, should be targeted for organic detection pyrolysis experiments on Mars. These findings are extremely timely, as exploration targets for Mars Science Laboratory include Vera Rubin Ridge (formerly known as "Hematite Ridge"), which may have formed from goethite precursors. Key Words: Mars-Pyrolysis-Jarosite-Goethite-Hematite-Biosignatures. Astrobiology 18, 454-464.
火星上的水铁矾具有重要的地质和天体生物学意义，因为它在酸性水条件下形成，而这种条件可能适合嗜酸生物生存。水铁矾可以提供环境背景，并且可能含有有机物。在火星表面寻找有机化合物最常用的提取技术是热解。然而，水铁矾的热分解会将氧气释放到热解炉中，从而降解有机信号。在许多沉积/成岩环境中，水铁矾与铁的氢氧化物针铁矿密切相关。在某些水条件下，针铁矿可以通过脱水形成赤铁矿，也可以直接从水铁矾形成。针铁矿和赤铁矿比水铁矾更适合用于寻找有机物的热解实验。对来自天然酸性溪流的样品的矿物学和有机化学分析表明，在富含针铁矿的层进行热解时，有机化合物的反应多种多样，但在富含水铁矾或混合水铁矾-针铁矿的样品中则反应较差。与水铁矾相关但本身不含水铁矾的针铁矿单元应成为火星有机探测热解实验的目标。这些发现非常及时，因为火星科学实验室的探测目标包括 Vera Rubin Ridge（以前称为“赤铁矿脊”），它可能是由针铁矿前体形成的。关键词：火星-热解-水铁矾-针铁矿-赤铁矿-生物特征。天体生物学 18，454-464。
