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The Martian near surface environment: Analysis of Antarctic soils and laboratory experiments on putative Martian organics.

机译：火星近地表环境：南极土壤分析和假定的火星有机物的室内实验。

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摘要

Understanding the physical properties as well as the potential for organic material in the Martian near-surface environment can give us a glimpse into the history of the site with regards to water, soil formation processes, as well as the conditions necessary for life. This work is done to support the interpretation of data from the Phoenix Mars Lander as well as other past and future landed missions.The Antarctic Dry Valleys are a hyper-arid cold polar desert that is the most Mars-like place on Earth. Soils from two different soil and climate regimes are analyzed to determine their physical properties such as mineralogy, particle size, shape, color, and specific surface area. These data are used to describe the sample locations in Antarctica and infer properties of Martian soils by comparison to Antarctic sites. I find that the particle size distribution can be used to determine the water history of the site and that the behavior of soluble species in the soil can also be used to trace the movement of water through the soil and could be instructive in understanding how soil organic material is processed by the environment.Continuing with the theme of soil organic matter, we revisit the Viking conclusions with regards to organics on Mars and look at the Phoenix data on the same subject. First, we assume that Mars receives organic material from meteoritic infall. These organics will be processed by chemical oxidants as well as UV light down to 200 nm. Chemical oxidation is predicted to produce molecules such as mellitic acid, which could preserve up to 10% of the original organic mass. Using mellitic acid and other similar organic molecules, we irradiate these molecules with Mars-like ultraviolet light, analyzing the gases that come off as irradiation takes place. We find that organic molecules can survive Mars-like UV conditions as layers of UV-resistant organics build up, shielding the remaining organic material. Additionally, the gas products of irradiation depend on the composition of the original organic molecule, implying that even irradiated molecules will carry some information about the composition of the original molecule.Finally, we take this irradiated organic/soil stimulant mixture and analyze it via pyrolysis, similar to the Viking GC/MS and TEGA instruments that are the only instruments operated on Mars capable of detecting organics. We find that the pyrolysis of mellitic acid (and other similar) molecules primarily produces inorganic fragments but that the reduced carbon fragments released depend on the composition of the original organic. However, the introduction of perchlorate, discovered on Mars by the Phoenix Lander, complicates the issue by creating the conditions for molecular oxidation. The high-oxygen content and high pyrolysis temperatures lead to organic combustion during thermal analysis, meaning that, regardless of the initial composition, most soil organics will be oxidized to CO2 during the detection process. By assuming that organic material was oxidized to CO2 in the Phoenix and Viking samples. We show that this assumption gives organic concentrations consistent with meteoritic accumulation rates. This finding reopens the possibility for organic molecules in the near-surface environment at the Viking and Phoenix landing sites.
机译：了解火星近地表环境中的物理特性以及有机物质的潜力，可以使我们瞥见该地点的历史，涉及水，土壤形成过程以及生命所必需的条件。这项工作是为了支持对凤凰号火星着陆器以及过去和将来的登陆任务的数据的解释。南极干旱谷是一块高干旱的极地沙漠，是地球上最像火星的地方。分析来自两种不同土壤和气候制度的土壤，以确定其物理性质，例如矿物学，粒度，形状，颜色和比表面积。这些数据用于描述南极的样本位置，并通过与南极地点的比较来推断火星土壤的特性。我发现颗粒大小分布可用于确定场地的水历史，并且土壤中的可溶性物种的行为还可用于追踪水在土壤中的运动，这对于理解土壤中有机物的含量具有指导意义。材料是由环境处理的。继续以土壤有机质为主题，我们重新审视关于火星上有机物的维京结论，并研究同一主题的Phoenix数据。首先，我们假设火星从陨石流中接收到有机物质。这些有机物将通过化学氧化剂以及低至200 nm的紫外线进行处理。预计化学氧化会产生诸如偏苯三酸的分子，该分子最多可保留原始有机物质的10％。我们使用偏苯三酸和其他类似的有机分子，用类似火星的紫外线照射这些分子，分析发生照射时散发出的气体。我们发现，随着抗紫外线有机物层的堆积，有机分子可以在类似火星的紫外线条件下生存，从而屏蔽了剩余的有机物质。此外，辐照的气体产物取决于原始有机分子的组成，这意味着即使被辐照的分子也会携带一些有关原始分子组成的信息。最后，我们将这种辐照的有机/土壤刺激剂混合物进行热解并进行分析类似于Viking GC / MS和TEGA仪器，后者是在火星上运行的唯一能够检测有机物的仪器。我们发现，偏苯三酸（及其他类似分子）分子的热解主要产生无机片段，但释放的还原碳片段取决于原始有机物的组成。然而，Phoenix Lander在火星上发现的高氯酸盐的引入，由于为分子氧化创造了条件，使问题复杂化了。高氧含量和高热解温度会导致热分析过程中的有机燃烧，这意味着，不管初始成分如何，大多数土壤有机物在检测过程中都会被氧化成CO2。通过假设在Phoenix和Viking样品中有机物质被氧化成CO2。我们表明，该假设给出的有机物浓度与陨石堆积速率一致。这一发现重新打开了维京号和菲尼克斯号登陆点附近表面环境中有机分子的可能性。

著录项

  • 作者

    Archer, Paul Douglas, Jr.;

  • 作者单位

    The University of Arizona.;

  • 授予单位 The University of Arizona.;
  • 学科 Geology.Chemistry Organic.Planetology.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 231 p.
  • 总页数 231
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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