The importance of Apollo in the advancement of planetology is self-evident. If only a single manned landing had been accomplished, the return of samples from another body in the solar system would have established Apollo as a milestone in the history of science. That the project was only a beginning goes without saying; it could hardly have been anything else. As Gerald Wasserburg wrote after Apollo 15, because the Apollo missions had all been targeted for areas that are not representative of the most widespread lunar surface features, "even on a coarse scale, we must consider the Moon as unexplored [italics in the original.]"21 The last two missions filled important gaps without altering the basic truth of this assessment. But even if all ten missions could have been flown as originally planned, they could not have adequately sampled an area as large as the moon and as heterogeneous as it turned out to be.
The materials returned by Apollo have not fulfilled the early hopes of the most optimistic scientists: that they would yield an understanding of the origin and evolution of the moon, the earth, and the solar system. This is no reflection on Apollo; those hopes - unrealistic, as it turned out - were based on excessive optimism and inadequate firm knowledge about the moon. "As is natural," Wasserburg commented, "the paucity of data did not inhibit the scientific community from either serious thought or rampant speculation on the origin of the Moon. The Apollo missions proved most of the speculation wrong."22 It was apparent after Apollo 12 that the moon's surface was far more complex than most cosmologists had suspected, and hopes for an explanation of the moon's origin rapidly waned. Whether the origin of the moon can ever be deduced from the Apollo samples is still an open question.
But whatever its shortcomings with respect to some hypothetical ideal, Apollo produced a store of scientific treasure whose value, although recognized, has only begun to be exploited by the scientific community. The lunar samples were, in Wasserburg's words, "the crown jewels of the scientific return of the Apollo missions." Before 1969 the only samples of extraterrestrial material known on earth were meteorites, which, as Wasserburg wrote, were less than satisfactory: they "come from unknown sources [and] were often terribly abused. [Yet] A large fraction of all human knowledge about the origin and age of the solar system . . . has been derived from the study of these objects."23 The Apollo samples changed all that. It seems probable that nothing like them will be available for many years to come.
No other effort to explore the moon compares with Apollo, although all added to the scientific knowledge of the moon. Ranger, which produced photographs showing craters and rocks as small as 1 meter (3 feet) in size, clarified some of the uncertainty about the nature of the lunar surface.24 The five Surveyor spacecraft, which landed in different types of terrain, carried instruments that demonstrated differences in the chemical makeup of lunar soil and identified the soil as "basaltic." Results from Surveyor allowed scientists to infer that the moon's interior was different from its surface.25
That unmanned samplers could be useful in lunar exploration was proved by Soviet space scientists, who sent two unmanned explorers (Luna 16, landed September 20, 1970, and returned to earth September 24, and Luna 20, landed February 22, 1972, returned February 25). Each returned approximately 100 grams (3 ounces) Of lunar soil from the eastern edge Of Mare Fecunditatis.* 26 In bringing back selected and documented samples from six locations on the moon, however, Apollo far surpassed all other efforts in whatever terms are used for comparison. Furthermore, the Apollo samples now stored on earth allow lunar research to continue, based on new concepts and using improved techniques and instruments. New concepts of the moon will be restricted only by the limited number of sites from which samples were taken.
* In 1976 one more Luna (Luna 24) returned a much larger sample from the southern edge of Mare Crisium in the moon's northeastern quadrant. Astronautics and Aeronautics, 1976, A Chronology, NASA SP-4021 (Washington, 1984) pp. 182-83.
21. Wasserburg, "The Moon and Sixpence of Science."
24. R. Cargill Hall, Lunar Impact: A History of Project Ranger, NASA SP-4210 (Washington, 1977), pp. 308-309.
25. L. D. Jaffe and others, "Principal Scientific Results From the Surveyor Program," in Surveyor Program Results, NASA SP-184 (Washington, 1969), pp. 13-17. Wasserburg remarks ("The Moon and Sixpence of Science") that with hindsight, the clues from Surveyor provided broad answers to the question of the moon's internal structure.
26. Astronautics and Aeronautics, 1970: Chronology on Science, Technology, and Policy, NASA SP-4015 (Washington, 1972), pp. 52-53; ibid., 1972, NASA SP-4017 (Washington, 1974), pp. 52-53.