火星含水硫酸铁的实验室模拟与遥感探测

Martian sulfates record important past and present environmental conditions of the Mars surface and subsurface. The occurrence of Fe-sulfates on Mars seen by orbital remote sensing is limited in spatial distribution as compared to those of Mg- and Ca-sulfates. Nevertheless, Fe-sulfates are found in surface and subsurface materials at both sites explored by the Spirit and Opportunity Rovers, which emphasizes their importance in Martian surface processes involving cycles of S and H2O.We propose to use a combination of laboratory and remote sensing studies for the purpose of establishing systematic spectroscopic studies of Martian ferric sulfates. On the basis of our previous work, we will continue to synthesis paracoquimbite, coquimbite and jarosite. The structures and the phase identification of synthesized ferric sulfates were firstly confirmed by XRD, then Raman, Mid-IR, and Vis-NIR spectra were obtained from them. The systematic spectroscopic studies will help to determine the relationship between crystal structures, vibrational modes and electron transitions in ferric sulfates. The study of stability fields of paracoquimbite and coquimbite will yield the pathways of phase transitions and phase diagrams, which will provide constraints for the remotely sensed analysis of ferric sulfates. We will also conduct the Mars remote sensing studies on ferric sulfates using data from CRISM aboard MRO. Our goal is to build links between orbital remote sensing and surface exploration through detailed laboratory experiments. The maps of ferric sulfates in typical Martian surface regions would help us to better understanding of the large scale stratigraphic distribution of Martian sulfates. Based on the "ground truth" results from a set of systematic laboratory experiments on the stability field of typical ferric sulfates, we will try to better understand the distribution and weathering mechanism of ferric sulfate on Mars.

火星硫酸盐记录了火星表层和次表层在过去和现在的重要环境条件。火星轨道遥感探测发现了大量的硫酸钙和硫酸镁沉积，而硫酸铁的分布则较少。然而勇气号和机遇号火星车在就位探测时发现了大量的硫酸铁沉积，这表明其在火星表面硫和水循环过程中具有重要作用。本研究将实验室合成九水硫酸铁（紫铁矾和针绿矾）和黄钾铁矾等新型含水硫酸铁晶体；利用X射线衍射（XRD）、拉曼光谱、红外、可见近红外等手段系统开展硫酸铁的物相鉴定，分析晶体的振动和电子跃迁对光谱特征的影响；开展九水硫酸铁的稳定场实验，获得硫酸铁晶体相变路径和相图，为火星含水硫酸铁的遥感研究提供实验室约束；在火星遥感研究方面，开展火星遥感数据（CRISM）与实验室光谱的联合研究，进行火星典型地区含水硫酸铁遥感光谱分析与反演，利用实验室光谱数据指导新型硫酸铁沉积区域的光谱指认，并进行硫酸铁填图与地质解译，为深入理解火星硫酸铁的空间分布与风化机制奠定基础。

硫酸铁盐记录了火星表层和次表层在过去和现在的环境条件，其种类和形成环境对认识火星水循环和环境演化历史具有重大研究价值。本项目开展了含水硫酸铁合成方法的实验探索，成功合成出副针绿矾、针绿矾、复铁矾、铁明矾、粒铁矾、黄钾铁矾等一系列硫酸铁晶体纯相；利用等离子体质谱仪（ICP-MS）、扫描电镜能谱仪（SEM-EDS）、X 射线衍射（XRD）、拉曼、中红外、可见近红外等手段系统表征硫酸铁晶体的化学成分、晶体结构和光谱学特性，构建了一套含水硫酸铁基础数据库；开展了含水硫酸铁的稳定场实验，获得了含水硫酸铁的相变路径、温度和湿度等热动力学参数；在火星硫酸盐遥感研究方面，项目组开展了Melas Chasma、Aureum Chaos、Jezero撞击坑等区域的多源火星遥感数据的综合分析（CRISM、HiRISE、HRSC、CTX等），利用上述数据库识别出叶绿矾、黄钾铁矾、羟基硫酸铁等含水硫酸铁矿物，理解这些区域的水成蚀变过程和硫酸铁的地质成因，获得环境和地质演化的新认识。此外，本项目利用拉曼成像技术研究了真实火星样品（火星陨石MIL 03346）为中含水硫酸铁等次生矿物的种类和空间分布，并将含水硫酸铁的研究思路进一步拓展至硫酸铝盐的研究，为这些硫酸盐在火星上的真实分布、遥感和就位探测提供重要参考。在本项目的支持下，项目组已在JGR:Planets、Icarus等期刊发表SCI论文6篇，在月球与行星科学大会（LPSC）、国际地质拉曼会议（GeoRaman）、中国地球科学联合学术年会等国内外会议发表会议论文19篇，申请国家发明专利5项。