Geological Background of the Chang'e 6 Landing Site and the Provenance of Returned Samples

Abstract

China's Chang'e-6 (CE-6) is the first mission in human history to return samples from the far side of the Moon. CE-6 landed in the mare plains of the southern Apollo basin (153.98°W, 41.63°S) within the South Pole-Aitken (SPA) basin on 2 June 2024 and returned 1,935.3 g of samples on 25 June 2024. The unique geological history of the Apollo basin offers an opportunity to address several important scientific questions in lunar science. To provide geological context for the analysis of the returned samples, we described the geology of the area surrounding the CE-6 landing site in detail. We interpreted that the region exhibits three periods of mare basaltic volcanism (EmSAp1, EmSAp2 and EmSAp3) separated by one billion years. CE-6 landed on the EmSAp2 unit, with a model age of ∼2.8 Ga. Several post-mare impacts occurring outside this region also contributed foreign materials to CE-6 landing site. We anticipate that the returned samples are dominated by local EmSAp2 materials, and may also include younger high-Ti basalt from the EmSAp3 unit, older low-Ti basalt from the EmSAp1 unit, ejecta from younger craters such as Chaffee S and O’Day, and ejecta from craters outside the SPA basin such as Vavilov, Crookes, and Das. The estimated total feldspathic exotic ejecta in the regolith of CE-6 sample zone is 30%. Our study indicates that the regolith in the CE-6 sampling area is rich in scientific value for understanding lunar volcanism and impact history and offers the possibility of further calibrating the lunar cratering chronology.