在水星表面，有些复杂撞击坑和撞击盆地的连续二次撞击坑(简称二次坑)与典型的二次坑不同，具有相对圆形的形态和相对离散的分布特征。此类撞击坑和撞击盆地一般形成于挥发分含量相对较高的低反照率物质中，意味着水星低反照率物质可能影响了撞击挖掘过程，可能是造成上述特殊形态的二次坑的原因。然而，水星壳层内的挥发分是否直接影响了撞击挖掘过程，并形成了较大的溅射角度，该问题依然有待于进一步解决。本课题拟通过二次坑的形态与分布特征研究水星壳层内的挥发分对撞击溅射角度的影响。首先，课题组研究水星表面具有相对圆形和离散分布的连续二次坑的撞击坑和撞击盆地的分布范围；然后，利用“信使号”探测器最新获取的全球多波段影像数据，绘制水星表面低反照率的物质单元分布；最后，通过GIS空间分析方法判定是否所有此类撞击坑和撞击盆地均无一例外地位于低反照率物质中，进而探讨壳层挥发分对撞击溅射角度的影响。

Secondary craters (secondaries) on continuous secondaries facies of some fresh complex impact craters and basins on Mercury have different morphological and distributional characteristics compared with typical lunar and mercurian secondaries, which have more regular shapes (usually more circular) and are less clustered in distribution. Such impact craters and basins usually form in low-reflectance material on Mercury, which has a higher abundance of volatiles compared with the global average. However, it is still not sure whether or not crustal volatiles on Mercury had affected the impact excavation process causing larger ejection angles. Here this proposal aims to study the effect of crustal volatiles on Mercury on impact ejection angles based on the morphological and distributional characteristics of secondaries. First, the global distribution of impact craters and basins that have more circular and less clustered secondaries on continuous secondaries facies will be collected. Using newly released global multiband mosaics of Mercury, the global distributional map of low-reflectance material on Mercury would be mapped. GIS spatial distribution analysis would be performed to verify whether or not all these craters and basins are associated with low-reflectance material, which would be meaningful to indicate whether or not crustal volatiles on Mercury had affected impact excavation process and impact ejection angles.