Geology and Scientific Significance of the Rumker Region in Northern Oceanus Procellarum: China's Chang'E-5 Landing Region

The Rumker region (41-45 degrees N, 49-69 degrees W) is located in northern Oceanus Procellarum of the Moon. Mons Rumker is the most distinctive geological feature in the area. The region is characterized by prolonged lunar volcanism (Late Imbrian Period to Eratosthenian Period), forming multiple geologic units in the area, including very low-Ti to low-Ti mare basalts, high-Ti mare basalts, and volcanic complexes. Each geologic unit has distinct element composition and mineral assemblages. The Rumker region, overlying the Procellarum KREEP Terrain, was selected as the landing region for China's Chang'E-5 lunar sample return mission. Prelanding analyses of the geologic context and scientific potential are reported in this contribution. We conducted detailed geological mapping using image, spectral, and altimetry data. Fourteen geological units were defined, a geologic map was constructed, and the geologic history was outlined. The western mare units (Im1, Im2, and Im3) are Imbrian-aged (similar to 3.4-3.5Ga) representing the major stage of lunar mare eruptive volcanism. The eastern young mare units (Em3 and Em4; <2Ga) are among the youngest mare basalts on the Moon. They have never been explored in situ or studied in the laboratory. We suggest that samples returned from the eastern mare unit (Em4) could answer many fundamental questions and that this unit should be listed as the top priority landing site for Chang'E-5 sample return mission. Plain Language Summary Recent studies find that the geological features and volcanic history of the Moon are far more complex than previously thought, and many of the most interesting areas have been neither explored nor sampled. One such area is the northern Oceanus Procellarum region which consists of very young (<2Ga) mare materials and hosts one of the largest volcanic complexes on the Moon (Mons Rumker). To document the main themes in the geological history, we studied the Rumker region using a wide variety of lunar orbital data. Surface composition, mineralogy, morphology, and topography were used to create a geological map in which we identified 14 geological units. We found old Ti-poor basaltic units (similar to some Apollo samples) and very young unsampled Ti-rich basaltic units (<1.5Ga). Samples from the young unsampled unit could answer many unresolved questions in lunar science because of its extremely young age. The area was selected as the landing region for China's Chang'E-5 lunar sample return mission in 2019. To maximize the scientific value of the returned samples, we assessed the scientific importance of each unit in our geologic map and suggest that the young mare basalt unit is the most valuable for sample return.