火星壁垒撞击坑成因机制分析及数值模拟

Rampart Crater is a kind of special craters in Mars surface found in 1973, which has a fluidized ejecta blanket and there is a steep rampart between its distal and the surrounding surface. The detailed formation process is still controversial although that water is involed has been widely accepted. The project intends to firstly analyse the elaborated topographic features of typical rampart craters based on the high resolution stereo images of HiRISE, and then make a statistics to the latitudinal distribution of characteristic parameters including the regonial onset diameters, ejecta mobility,etc. The detailed formation process will be analysed based on these regularities with the method of the numerical simulation. Finally the formation mechanism and the related scientific significance will be discussed in depth. The main study contents include obtaining the high-precision DEM from high resolution stereo images of HiRISE, the calcultion and statistics of related characteristic parameters, the mechanical models of the target materials in the impact process, the ANEOS equation of state of the mixture between the water and Mars surface rocks, the mechanical description of the surrounding ejecta blanket in its formation process, and the analysis of the formation mechanism of the rampart craters.

壁垒撞击坑是火星表面一种特殊类型的撞击坑，它发现于1973年，具有流态化的溅射席，其末端与周围地表形成陡峭的壁垒，水参与到其形成过程已经得到了广泛的共识，但对其具体形成过程仍有争议。本项目拟首先利用高分辨率的HiRISE立体影像分析典型壁垒撞击坑精细的地貌形态，然后综合利用火星遥感影像数据统计包括区域最小直径、溅射席流动性等有关壁垒撞击坑的特征参数在火星表面随纬度的分布规律，在此基础上利用数值模拟分析其形成的具体过程，最后根据数值模拟的结果深入分析壁垒撞击坑的形成机制以及相关的科学意义。 主要研究内容包括：利用高分辨率的HiRISE立体影像提取高精度的DEM；壁垒撞击坑相关特征参数的计算与统计；撞击过程中靶区物质的力学模型；由水和火星表层岩石组成的混合物的ANEOS状态方程；壁垒撞击坑周围溅射席形成过程中的力学描述；壁垒撞击坑形成机制分析。

壁垒撞击坑是火星表面一种特殊的撞击坑，它具有流体化的溅射席，这可能是水参与撞击过程的结果，但是前期研究并未针对性地分析其具体行程过程。本项目结合遥感观测、数值模拟、物理实验三种重要方法，对壁垒撞击坑的形成机制进行分析，得到的主要结论包括：（1）壁垒撞击坑的溅射席流动性具有明显的纬度相关性，高纬度地区的溅射席具有更强的流动性，而且具有较小的起始直径；（2）数值结果表明地下冰层的存在严重影响了撞击坑的形态与溅射物的分布，并且地下冰层厚度、深度与溅射席的含水量呈非线性关系；（3）针对壁垒撞击坑的形成开展的物理实验表明液态水的存在是形成壁垒撞击坑的必要条件，固态水冰在撞击过程中熔化量不足以形成壁垒撞击坑。