Lunar regolith thickness deduced from concentric craters in the CE-5 landing area

Abstract

Lunar regolith is the layer of fragmented and unconsolidated rock material that is repeatedly stirred and overturned on the lunar surface. It can provide critical information about lunar geologic processes (e.g., impact, volcanism) and the space environment. China's Chang'E-5 (CE-5) mission, which will be launched in 2019, will land on the lunar near-side surface and return at least 2 kg of lunar regolith through surface collection and by boring a hole no <2 m in depth. This study focuses on the depth of lunar regolith in the planned CE-5 landing area, which may be important for sampling activity and related scientific research. The traditional crater morphological method uses the dimensions of particular craters to derive the lunar regolith thickness, i.e., the lunar regolith thickness is estimated through the characterization of concentric, flat bottomed, and central mound craters. However, recent studies show that flat bottomed and central mound craters can also be formed by clustered projectiles. Therefore, only concentric craters were used to estimate the lunar regolith depth in this study, and subsequent morphological analysis indeed indicates that flat bottomed and central mound craters were primarily formed from secondary clustered impacts in this area. The precise locations and sizes of the selected concentric craters were determined from a high-resolution seamless Digital Orthophoto Map (DOM) of the CE-5 landing area, which was generated by our team using 765 selected LROC NAC images. All the concentric craters, including the inner and outer crater rims, were then mapped in the DOM. Local lunar regolith depths were derived according to the previously established relationship between lunar regolith depth and the inner and outer diameters. The results show that the lunar regolith in the area ranges from 0.74 m to 18.00 m, with a mean of 7.15 m, and is much shallower in the southeast than in other areas.