Probing hydrous phases on Mars using martian meteorites

长期以来，火星一直是寻找地球以外可能存在生命的主要目标，这主要是因为有广泛的证据表明，火星表面曾经有水流动。水是地球上生命的基本成分，但仅仅发现水还不足以确定生命所必需的成分是否曾经存在过。没有适宜居住的气候和磷的生物可利用性（作为DNA和RNA等生命的基本组成部分），火星上的生命不太可能有机会进化。我们的具体目标是：1)利用扫描透射电子显微镜（STEM）和原子探针断层扫描（APT）在纳米尺度上对熔融包裹体中的含水火星磷酸盐矿物进行D/H、H2O和OH的相关结构和化学观察。2)利用纳米二次离子质谱法（NanoSIMS）确定在激波变质过程中，火星硫化物矿物内部的硫同位素（用作火星大气过程的示踪剂）是如何受到干扰的。3)确定火星大气是否在火星表面喷出时被冲击熔化的硫化物矿物所吸收。如果成功，这个项目将极大地加强对火星上生命成分何时以及如何形成的限制。两个这样的矿物群——磷酸盐（火星陨石中唯一含oh的矿物之一）和硫化物是这项研究的重点。火星陨石的分析是复杂的，因为所有的火星陨石本质上都是“震荡”的，在从火星表面喷出的过程中，在着陆地球之前经历了强烈的变形。这些冲击事件会导致变形、矿物转化和化学反应，包括通过冲击压缩将火星大气纳入某些矿物和玻璃中。激波变质作用的影响是如此广泛，以至于同位素的非均质性往往是在纳米尺度上引起的，这使得用传统技术准确表征火星物质的努力变得更加复杂。解决这些纳米尺度的异质性是我们的核心目标。我们只能通过EMSL访问相关的STEM和APT方法，并且已被证明对APT分析的目标选择非常宝贵。此外，NanoSIMS将用于帮助解决硫化物中的同位素非均质性。如果成功，这个项目将极大地加强对火星上，甚至整个太阳系的生命成分可能在何时以及如何存在和演化的研究。回答这些问题将使我们能够更准确地预测火星上生命所需的磷和水的可用性、火星水的起源以及火星大气的演变，这在解释含有大气和水相互作用同位素特征的火星矿物分析时尤为重要。

Mars has long been the primary target in the search for possible life beyond our planet, mainly due to widespread evidence that water once flowed on its surface. Water is an essential ingredient for life on Earth, but the identification of water alone is not enough to determine if the ingredients necessary for life were once present. Without a habitable climate, and bioavailability of phosphorous (as an essential component in the building blocks of life such as DNA and RNA) it is unlikely that life on Mars could have had the chance to evolve. Our specific aims are: 1) To study hydrous Martian phosphate minerals in melt inclusions using correlative structural and chemical observations of D/H, H2O, and OH on the nanoscale using Scanning Transmission Electron Microscopy (STEM), and Atom Probe Tomography (APT). 2) To determine how sulfur isotopes (used as tracers of atmospheric processes on Mars) have been disturbed within Martian sulfide minerals during shock metamorphism using nano Secondary Ion Mass Spectrometry (NanoSIMS). 3) To determine if Martian atmosphere was incorporated into shock-melted sulfide minerals during ejection from the Martian surface. If successful, this project will greatly strengthen efforts to constrain when and how the ingredients for life on Mars. Two such mineral groups - phosphates as one of the only OH-bearing minerals in Martian meteorites, and sulfides are the focus of this study. The analysis of Martian meteorites is complicated since all Martian meteorites are inherently `shocked', undergoing intense deformation during ejection from the Martian surface before landing on Earth. These shock events can cause deformation, mineral transformations, and chemical reactions including the incorporation of Martian atmosphere into certain minerals and glasses through shock compression. The effects of shock metamorphism are so extensive that isotopic heterogeneities are often induced at the nanoscale, complicating efforts to accurately characterize Martian materials with conventional techniques. Resolving these nano-scale heterogeneities is central to our goals. The correlative STEM and APT approach is only accessible to us through EMSL, and has proved invaluable for target selection for APT analysis. Additionally, NanoSIMS will be used to help resolve isotopic heterogeneities within sulfides. If successful, this project will greatly strengthen efforts to constrain when and how the ingredients for life on Mars, and potentially throughout the Solar System, may have existed and evolved. Answering these questions will allow for a more accurate prediction of phosphorous and water availability for life on Mars, the origin of Martian water, and the evolution of the Martian atmosphere which are especially important when interpreting analyses of Martian minerals that contain isotopic signatures of atmospheric and water interactions.