Preservation of organic matter by reactive iron species on Mars relevant to Mars Sample Return

与火星样本返回相关的火星上活性铁物种对有机物的保存

• 批准号: 2489834
• 金额: --
• 依托单位: University of Stirling
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2489834
• 关键词: Preservation; organic; matter; reactive; iron

Background: Both NASA's Mars 2020 Perseverance rover and ESA's ExoMars rover Rosalind Franklin will be looking for signs of potential life on Mars. Perseverance launched in July 2020 and will land at Jezero crater in February 2021. Jezero crater once held a lake and has delta-like deposits at the mouth of inflow channels as prioriy area for its investigations. Perseverance will kick-off the Mars Sample Return effort by collecting and caching samples for return to Earth by subsequent missions. Rosalind Franklin will launch in 2022 and land at Oxia Planum on Mars. This area is characterized by wide-spread clay mineral deposits and includes subtle fluvial channels and delta-like deposits as well. Rosalind Franklin id equipped with a drill to collect samples from up to 2 m depth to look for organic material preserved from the hars radiation environment on Mars' surface.Iron minerals play a key role in the sequestration and preservation of carbon. Over 20% of organic carbon in sediments on Earth is directly bound to reactive iron phases (Lalonde et al. 2012), also dubbed the Rusty Carbon Sink. The organic matter-iron mineral complexes mutually stabilize each other against organic matter degradation and mineral transformation, whereby the iron species involved often occur in nanoparticulate and X-ray amorphous forms (Schröder et al. 2016). Upon diagenesis, however, the redox properties of iron facilitate the oxidation of organic matter (Posth et al. 2013; Schröder et al. 2016; Tan et al. 2020). On that basis, a good target for the search for potential organic biosignatures would be rich in nanophase iron phases and X-ray amorphous minerals. Aqueously altered rocks and soils investigated in Gusev crater and at Meridiani Planum on Mars contain abundant nanophase iron oxides (e.g. Morris et al. 2019), and 20-60 wt% of minerals in fluvio-lacustrine deposits in Gale crater are X-ray amorphous and this amorphous phase is rich in iron (e.g. Rampe et al. 2017, 2019). Similar deposits should be targeted in Jezero crater and at Oxia Planum to look for organic biosignatures. However, the difficulty is to recognize deposits rich in reactive iron phases (and therefore lacking a diagenetic or metamorphic overprint). The Mars Exploration Rovers Spirit and Opportunity who landed at Gusev crater and Meridiani Planum, respectively, had Mössbauer spectrometers as their principle mineralogical tool, while the MSL Curiosity rover at Gale crater used XRD. Perseverance and Rosalind Franklin will use Raman spectrometers for mineralogical analyses.Objectives:- Investigate sediments and sedimentary rocks of different ages, which contain reactive iron mineral phases (i.e. lack diagenetic or metamorphic overprint) using XRD, Mössbauer and Raman spectroscopy- Develop Mössbauer spectroscopy as a tool to be used for the analysis of returned samplesMethodology: We will identify and collect a series of sediments and sedimentary rocks rich in reactive iron mineral phases with a range of different ages. These will be investigated for their mineralogy using XRD, Mössbauer and Raman Spectroscopy, plus XRF for elemental analysis and SEM for spatial charactiersation. We will measure organic carbon content and quantify specific carbon compounds. Different Mössbauer spectroscopy applications - transmission and low-temperature measurements; non-destructive backscattering applications; synchrotron-based applications - will be used and optimized with a view to apply the to the investigation of returned samples.

背景：美国宇航局的火星2020毅力探测器和欧空局的ExoMars探测器罗莎琳德富兰克林都将在火星上寻找潜在生命的迹象。Perseverance于2020年7月发射，将于2021年2月降落在热泽罗陨石坑。热泽罗火山口曾经有一个湖泊，在流入通道的入口处有三角洲状的沉积物，作为其调查的优先区域。毅力号将通过收集和缓存样本以供后续任务返回地球来启动火星样本返回工作。罗莎琳德富兰克林将于2022年发射升空，降落在火星上的奥夏平原。这一地区的特点是广泛分布的粘土矿床，并包括微妙的河流和三角洲的沉积以及。罗莎琳德富兰克林配备了一个钻孔机，可以从2米深的地方采集样本，以寻找火星表面严酷的辐射环境中保存下来的有机物质。铁矿物在碳的封存和保存中起着关键作用。地球沉积物中超过20%的有机碳直接与活性铁相结合（Lalonde等人，2012年），也被称为锈碳汇。有机物-铁矿物复合物相互稳定，防止有机物降解和矿物转化，其中所涉及的铁物质通常以纳米颗粒和X射线无定形形式存在（Schröder等人，2016）。然而，在成岩作用后，铁的氧化还原特性促进了有机质的氧化（Posth等人，2013; Schröder等人，2016; Tan等人，2020）。在此基础上，寻找潜在有机生物特征的一个很好的目标将是富含纳米铁相和X射线无定形矿物。在古谢夫陨石坑和火星子午线平原调查的水蚀变岩石和土壤含有丰富的纳米相氧化铁（例如Morris等人，2019），盖尔陨石坑河湖沉积物中20 - 60重量%的矿物是X射线无定形的，这种无定形相富含铁（例如Rampe等人，2017，2019）。应在热泽罗陨石坑和Oxia Planum寻找类似的沉积物，以寻找有机生物特征。然而，困难在于识别富含活性铁相的矿床（因此缺乏成岩或变质叠加）。分别在古谢夫陨石坑和子午线平原着陆的火星探测漫游者勇气号和机遇号使用穆斯堡尔光谱仪作为其主要矿物学工具，而在盖尔陨石坑着陆的MSL Currency漫游者则使用XRD。Perseverance和Rosalind富兰克林将使用拉曼光谱仪进行矿物学分析。目标：-使用XRD、穆斯堡尔和拉曼光谱法调查不同年龄的沉积物和沉积岩，这些沉积物和沉积岩含有活性铁矿物相（即缺乏成岩或变质叠印）-开发穆斯堡尔光谱法作为用于分析返回样品的工具方法：我们将识别和收集一系列不同年龄的富含活性铁矿物相的沉积物和沉积岩。将使用XRD、穆斯堡尔谱和拉曼光谱，加上用于元素分析的XRF和用于空间表征的SEM对其矿物学进行研究。我们将测量有机碳含量并量化特定的碳化合物。将使用和优化不同的穆斯堡尔光谱应用-透射和低温测量;无损反向散射应用;基于同步加速器的应用-以期将其应用于返回样品的调查。