Soviet lunar sample return missions: Landing site identification and geologic context

The Lunar Reconnaissance Orbiter Camera (LROC) imaged the landing sites and spacecraft from the Soviet Unionʹs Luna robotic sample return program (Luna 16, 20, and 24) allowing their locations to be determined with unprecedented precision and, more importantly, for the geologic context of the landing sites to be firmly established. Uncertainties in the position of the landing sites are now 25 m (or better), as opposed to kilometers prior to LROC observations. Because of the past uncertainty of the locations, as well as the fact that two of the Luna missions were conducted at night, the geologic context of the samples was only poorly known. LROC images reveal that the Luna 24 sample was collected on the rim of a small impact crater, providing an explanation for the compositional and maturity discrepancy that has existed for the past three decades between samples and remote sensing of the Mare Crisium surface. The location of the unsuccessful Luna 23 spacecraft is also determined and the nature of the failure confirmed.