Clarification of Sources of Material Returned by Luna 24 Spacecraft Based on Analysis of New Images of the Landing Site Taken by Lunar Reconnaissance Orbiter1

摘要

We describe the results of the geologic analysis of high-resolution (0.5 m/px) LROC NAC images of the landing site of the Luna 24 spacecraft, which landed in the southeastern part of Mare Crisium, drilled a borehole to the depth of ~2 m and recovered a core, which was then delivered to the Earth. LROC NAC images show that the spacecraft landed on the rim of the 65—m crater Lev. Image analysis was aided by calculations of the expected thickness of ejecta from crater Lev found to be 0.5—1 m. Using these calculations and the results of photogeologic analysis, we reconsidered the characteristics of the Luna 24 core material. This led to an understanding of the geologic position of different parts of the Luna 24 core and allowed us to distinguish in the core the intervals dominated by: 1 —effects of arrival of ejecta from the 6.5—km crater Fahrenheit (Zone TV), 2—gradual reworking of the local regolith by small impacts (Zones II and III), and 3— emplacement of ejecta of Lev crater, which is a secondary of the distant 22-km crater Giordano Bruno (Zone I). This understanding allowed us to propose that some additional new analyses of the Luna 24 material be undertaken, with emphasis on the study of Zone IV and Zone I. Additional analysis of zone IV could search for and identify material of ejecta from the crater Fahrenheit and their comparisons with local materials, while new analysis of Zone I could study the material derived from the deepest parts of the local regolith and search for material of the impactor (ejecta from the very young Giordano Bruno crater on the lunar farside) that formed Lev crater.