The inner wall of Alder is rough and slightly terraced, with the material scattered across the edges of the otherwise relatively flat interior floor. There are several low central ridges lying along a band from the midpoint toward the eastern rim. A small crater lies on the eastern inner slopes. The crater is otherwise free of significant impacts within the rim.
Alder is associated with the only area in the basin not dominated by the pyroxene rocks typical of lunar lowlands. This alder ejecta area is on spectrographic evidence instead principally anorthosite rock, typical of the lunar highlands.[citation needed]
Satellite craters
By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Alder.
Alder
Latitude
Longitude
Diameter
E
47.6° S
172.3° W
16 km
References
Andersson, L. E.; Whitaker, E. A. (1982). NASA Catalogue of Lunar Nomenclature. NASA RP-1097.
Menzel, D. H.; Minnaert, M.; Levin, B.; Dollfus, A.; Bell, B. (1971). "Report on Lunar Nomenclature by the Working Group of Commission 17 of the IAU". Space Science Reviews. 12 (2): 136–186. Bibcode:1971SSRv...12..136M. doi:10.1007/BF00171763. S2CID122125855.
Taylor, G. J. (July 1998). "The Biggest Hole in the Solar System". Planetary Science Research Discoveries. Archived from the original on 20 August 2007. Retrieved 2007-07-25. (This article on South Pole-Aitken (SPA) basin mentions Alder crater.)