| Summary: | Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole-Aitken basin (>2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta. © 1992 American Association for the Advancement of Science. 30 August 1991; accepted 11 December 1991. We thank the Galileo Project Office, the National Aeronautics and Space Administration, and numerous individuals who participated in the mission planning and initial data analysis for help and support including T. Becker, L. Bolef, H. Breneman, E. Dejong, E. Fischer, L. Gaddis, P. Helfenstein, H. Hoffmann, R. Jaumann, J. Moersch, S. Murchie, J. Oberst, J. Plutchak, M. Robinson, D. Rudy, R. Sullivan, J. Sunshine, L. Wainio, and D. Williams. Helpful comments on earlier drafts of this manuscript were provided by P. Pinet, S. Murchie, J. Sunshine, E. Fischer, and an anonymous reviewer.
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