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，水曾经在其表面流动。水是地球上生命的重要组成部分，但仅仅确定水并不足以确定生命所需的成分是否曾经存在。如果没有适宜居住的气候和磷的生物利用度（作为生命的基本组成部分，如DNA和RNA），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）和原子探针层析成像（APT）在纳米尺度上对D/H、H_2O和OH进行相关的结构和化学观测，研究熔融包裹体中的含水火星磷酸盐矿物。2)使用纳米二次离子质谱法（NanoSIMS）确定硫同位素（用作火星大气过程的示踪剂）在冲击变质过程中如何在火星硫化物矿物中受到干扰。3)为了确定火星大气是否在从火星表面喷出的过程中融入了冲击熔化的硫化物矿物。如果成功，这个项目将大大加强努力，以限制何时以及如何在火星上的生命成分。两个这样的矿物组-磷酸盐作为火星陨石中唯一的OH-轴承矿物之一，硫化物是本研究的重点。对火星陨石的分析是复杂的，因为所有火星陨石都是固有的"震动"，在降落在地球上之前从火星表面弹射出来的过程中经历了强烈的变形。这些冲击事件可能会导致变形，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。冲击变质作用的影响是如此广泛，以至于同位素的不均匀性往往在纳米尺度上被诱导，这使得用传统技术准确表征火星物质的工作变得复杂。解决这些纳米尺度的异质性是我们目标的核心。相关的STEM和APT方法只能通过EMSL访问，并且已经证明对于APT分析的目标选择是非常宝贵的。此外，NanoSIMS将用于帮助解析硫化物中的同位素异质性。如果成功，这个项目将大大加强努力，以限制火星上的生命成分以及可能在整个太阳系中存在和进化的时间和方式。研究这些问题将有助于更准确地预测火星上生命的磷和水的可用性，火星水的起源以及火星大气的演变，这在解释包含大气和水相互作用的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.