Geological mapping and chronology of lunar landing sites: Apollo 15

Abstract

Apollo 15 was the first extended exploration mission to the Moon. The data acquired from the Apollo 15 mission constitutes a comprehensive geological dataset, significantly enhancing our understanding of volcanic, impact and other geological processes, and the chronological and thermal evolution of the Moon. Moreover, the Apollo 15 data provide a critical calibration point for the lunar cratering chronology function. This chronology is established through the systematic correlation of crater size-frequency distributions (CSFDs) with radioisotopic ages of samples from the Apollo, Luna, and Chang'e landing sites. Establishing this link between samples and CSFDs necessitates a thorough understanding of the geology of the landing sites. In this study, we present a newly developed, detailed regional geological map of the Apollo 15 landing site, utilizing modern data. Our new geological map enables the identification of homogeneous regions suitable for new CSFD measurements, from which updated N(1) values (i.e., the cumulative number of craters with diameters ≥1 km) can be derived for the corresponding geological units. Furthermore, this geological map addresses outstanding scientific questions, which have been outlined as objectives for the 500-day Hadley Max design reference mission (DRM) (Daniti et al., 2024). The new calibration point obtained from comparing these updated N(1) values with sample ages was found to be consistent with the lunar chronology proposed by Neukum (1983). This consistency, in conjunction with our previous research, reinforces the validity of Neukum's lunar cratering chronology. We summarize the key outstanding scientific questions identified by the new geologic map as a basis for future human and robotic lunar exploration of the Moon.