Zhen-Yu, Tao (Wuhan University of Hydraulic and Electric Engineering) | Li-Ming, Zhang (Wuhan University of Hydraulic and Electric Engineering) | Tie-Min, Chen (Wuhan University of Hydraulic and Electric Engineering)
Haimson, Bezalel C. (Geological Engineering Program, Department of Materials Science and Engineering, University of Wisconsin) | Zhao, Zhongliang (Geological Engineering Program, Department of Materials Science and Engineering, University of Wisconsin)
Lunar surface morphology and the physical characteristics of materials at the surface are products of planetary processes operating on ancient igneous rocks that solidified at or near the surface of the Moon. The rocks are similar to terrestrial igneous rocks but the processes are quite different from those commonly observed on Earth. Hypervelocity impact has been the dominant process active in the erosion, transportation, and metamorphism of lunar surface materials throughout most of lunar history. The impacts have formed craters with diameters spanning more than ten orders of magnitude (<0.1 millimeter to >1,000 kilometers). When a meteorite strikes the lunar surface, some of the target material melts; shock waves shatter a much greater volume. Part of the molten material and some of the fragments are ejected from the crater. Much of the ejected material travels only a short distance from the point of impact. Some fragments achieve escape velocity; a few have traveled to Earth. Intermixed fine-grained material and rock fragments mantle bedrock at most localities on the Moon. This regolith is typically fine-grained near the surface, but larger blocks are abundant on the surface near the rims of craters that penetrate the fine-grained material. Astronaut observations and measurements on the lunar surface provide valuable constraints on in- terpretations of the variable regolith thickness from orbital photography and other remote sensing data collected by the Apollo program. Studies of lunar samples at laboratories around the world during the past two decades have thoroughly characterized the larger rock samples from the six Apollo landing sites. Apollo remote sensing data and laboratory studies of small fragments in the lunar breccias provide a basis for characterizing surface materials in areas of the Moon not yet explored by humans.