The Chang’e-5 (CE-5) mission is China’s first lunar sample return mission. CE-5 landed at Northern Oceanus Procellarum (43.1°N, 51.8°W) on December 1, 2020, collected 1731 g of lunar samples, and returned to the Earth on December 17, 2020. The CE-5 landing site is ~170 km ENE of Mons Rümker , characterized by some of the youngest mare basalts (Em4/P58) on the Moon [2,3], which are never sampled by the Apollo or Luna missions . This study describes the geologic background of the CE-5 landing site in order to provide context for the ongoing sample analysis.
Northern Oceanus Procellarum
Northern Oceanus Procellarum is in the northwest lunar nearside, and the center of the Procellarum-KREEP-Terrane , characterized by elevated heat-producing elements and prolonged volcanism. This region exhibits a huge volcanic complex, i.e., Mons Rümker , and two episodes of mare eruptions, i.e., Imbrian-aged low-Ti mare basalts in the west and Eratosthenian-aged high-Ti mare basalts (Em3 and Em4/P58) in the east . The longest sinuous rille on the Moon , Rima Sharp, extends across Em4/P58. Both the Imbrian-aged (NW-SE) and Eratosthenian-aged (NE-SW) basalts display wrinkle ridges, indicating underlying structures, with different dominant orientations .
Young Mare Basalts
The Em4/P58 mare basaltic unit, on which CE-5 landed, is one of the youngest mare basalts on the Moon. Various researchers found different CSFD results; however, all of them point to an Eratosthenian age for Em4/P85 (1.21 Ga , 1.33 Ga [7,8], 1.53 Ga , 1.91 Ga ), and there are minor age variations across Em4/P58 . Em4/P58 mare basalts have high-Ti, relatively high-olivine and high-Th abundances, while clinopyroxene is the most abundant mineral type [2,3]. Em4/P58 mare basalts cover an area of ~37,000 km2, with a mean thickness of ~51 m and volume of ~1450-2350 km3 . No specific source vents were found within the unit, and Rima Sharp is the most likely source region for the Em4/P58 mare basalts .
Scientific Significance of the Returned Samples
The scientific significance of the young mare basalts is summarized in our previous studies [2,3]. In , we first summarized the 27 fundamental questions that may be answered by the returned CE-5 samples, including questions about chronology, petrogenesis, regional setting, geodynamic & thermal evolution, and regolith formation (Tab. 1 in ), especially calibrating the lunar chronology function, constraining the lunar dynamo status, unraveling the deep mantle properties, and assessing the Procellarum-KREEP-Terrain structures.
 Zhao J. et al. (2017) JGR, 122, 1419–1442.  Qian Y. et al (2018) JGR, 123, 1407–1430.  Qian Y. et al. (2021) EPSL, 555, 116702.  Tartèse R. et al. (2019) Space Sci. Rev., 215, 54.  Jolliff B. L. et al. (2000) JGR, 105, 4197–4216.  Hurwitz D. M. et al. (2013) Planet. Space Sci., 79–80, 1–38.  Hiesinger H. et al. (2003) JGR, 108, 1–1 (2003).  Hiesinger H. et al. (2011) Geol. Soc. Am., 477, 1–51.  Morota T. et al. (2011) EPSL, 302, 255–266.