Geological investigations of Luna 17, Apollo 15 and Chang’E-3 landing sites at Mare Imbrium of the Moon

Abstract

The Imbrium basin is one of the most prominent geologic units on the lunar nearside, and also significant exploration target for soft-landing missions. Till now, three lunar missions, USSR’s Luna 17, American Apollo 15 and Chinese Chang’E-3, have successfully soft-landed and conducted surface investigation at this basin. Employing the surface images and other data acquired by the three missions, we analyze the geologic characteristics of the three landing sites, mainly focusing on the regional geologic context, impact craters, surface boulders and regolith materials. We find that, the Lunar 17 and Chang’E-3 spacecraft landed on the relatively younger Eratosthenian mare basalt units, respectively, where massive basaltic bedrocks are exposed at the wall and rim of some small craters, and some of these exposed boulders present columnar jointing, while the Apollo 15 landed on the relatively older Imbrian lava plains, where surface boulders are seldom present. There exposed some layered basalts at the wall of the Hadley Rille, and columnar jointing structure is also observed at some boulders exposed at the rille floor and rim. We observe some possible lineaments on the surface images. We propose that these possible lineaments are caused by slightly undulant lunar surface illuminated under relatively low sun elevation angles, which is supported by our simulation experiments. The comparison of the three landing sites indicates that impacting history, volcanic activities, space weathering and other important geologic processes are regionally and locally inhomogeneous on the Moon, future lunar surface in-situ and sample-return missions will strengthen our understanding of the geologic evolutionary history of the Moon.