“嫦娥4号”月球背面着陆区月壳及深部结构特征

Crustal and Subsurface Structures of Chang'E-4 Lunar Farside Landing-Site

深部月壳和月幔物质结构是月球科学探测的关键问题之一。"嫦娥4号"初步将月球背面南极-艾肯(South Pole-Aitken,SPA)盆地内的冯·卡门(Von Kármán)撞击坑作为着陆点,具有重要的科学研究价值。结合月球重力、地形、布格重力、月壳厚度等地球物理数据,综合对冯·卡门撞击坑的月壳及其深部结构特征进行了分析。结果显示:冯·卡门撞击坑重复撞击到南部的冯·卡门M撞击坑上,后者的中央峰具有明显的布格正重力异常和线性的布格重力梯度特征,显示出高密度的幔部物质向上涌起;冯·卡门撞击坑极有可能穿透了该区域的整个月壳,并挖掘出了深部月幔的物质;该区域南部月壳厚度较薄小于5 km,北部平均月壳厚度在15～20 km,月壳平均密度为2 630 kg·m^(-3),比背面高地月壳密度高,且平均孔隙度为9%,低于月球的平均孔隙度12%。

As the selected landing-site for Chinese Chang＇e-4 mission, the Von Kármán crater, located in the central region of the South Pole-Aitken（SPA） basin, opens an important window to study the lunar farside crust. In this paper, the newly obtained gravity, topography, Bouguer gravity/gradient and crustal thickness data are used to comprehensively study the crustal and subsurface structures of the Von Kármán crater. Results show that the Von Kármán crater is located in the northern part of a preexisted impact crater Von Kármán M, which has obvious central positive Bouguer gravity anomaly and linear Bouguer gravity gradient features, indicating possible dikes and dense materials beneath the crater. The Von Kármán crater is likely to penetrate through the entire crust of the SPA and excavated the deep mantle materials. The crustal thickness map shows that the southern crust of the Von Kármán crater is as thin as 5 km and the northern area has an average crust thickness between 15 and 20 km. The bulk density of the Von Kármán crater is 2630 kg·m^-3, which is about 100 kg·m^-3 higher than that of the farside highland crust. The grain density of this region is 2890 kg m^-3, suggesting an average porosity of 9%, which is slightly lower than that of the lunar crust.