Geological Chronicle
Alder is located in the southern hemisphere on the far side of the Moon, set within the South Pole-Aitken basin southeast of Von Kármán. Bose lies southeast of the rim, and Boyle sits to the south-southwest. The crater dates from the Late Imbrian epoch, with an age of around ~3.5+0.01−0.2 Ga. Its inner wall is rough and slightly terraced, with material scattered across the edges of an otherwise relatively flat interior floor, and a small crater sits on the eastern inner slopes.
Across the interior, several low central ridges lie along a band from the midpoint toward the eastern rim. Two small central mounds share a similar form but display distinctly different spectra, with the western mound strongly mafic and the eastern mound showing more plagioclase. Alder is associated with the only area in the basin not dominated by pyroxene rocks typical of lunar lowlands, with spectrographic evidence indicating that this ejecta area is principally anorthosite rock, typical of the lunar highlands.
Ejecta from this impact extends across the surrounding terrain, where it forms a major layer at the Chang'e 4 landing zone located within Von Kármán crater. The crater is named after German chemist Kurt Alder, a 1950 Nobel laureate, and the International Astronomical Union formally adopted the designation in 1979.