Apollo 17 and the Moon

Apollo 17 was not the last flight of humans to the Moon. More lunar exploration and even lunar settlement will occur, baring the future stagnation or disappearance of our civilization. Exploration and scientific investigations in the earth sciences are rarely complete, particularly for studies related to a specific field site. A long hiatus between field investigations may occur, but other forms of investigation, directly or indirectly related, continue. Apollo 17's field study of the Valley of Taurus-Littrow on the Moon in 1972 and subsequent examination of its significance to our understanding of the origin and evolution of that small planet and of our own constitute a good example of these facts of scientific life. As the third of the specifically “science” missions to the Moon in the twentieth century, Apollo 17 actually became the last lunar landing of the Apollo Program in September 1970 rather than on 11 December 1972 when the mission reached Taurus-Littrow. The National Aeronautics and Space Administration (NASA) and the Administration of President Richard M. Nixon, with the acquiescence of the Congress, had concluded that no further planned amortization of the American taxpayer's investment in deep space exploration would be undertaken. The scientists became increasingly interested in an unnamed, 2300-m deep, 50-km long valley, radial to the 740-km diameter circular basin, Serenitatis, that cut through the Taurus Mountain ring near the crater Littrow. This Valley of “Taurus-Littrow,” however, was not a favorite of the operational mission planners. In spite of the pinpoint landing accuracy they had demonstrated on all previous missions since Apollo 11, the narrow valley, the mountainous approach, and the high valley walls gave the planners pause. Their legitimate concerns were compounded by the relatively short time, only 14 minutes, for navigational updates after acquisition of communications from the lunar module, Challenger, as its last orbit before landing carried it around the Moon from the farside. Initially, trajectory calculations indicated that three-sigma errors, the normal extremely conservative planning limit, might result in hitting the side of the northern mountain wall. Gradually, however, refinements in navigational techniques for the mission and the inevitable synergistic give and take that so characterized Apollo interactions narrowed the three-sigma errors to about 1 km, the limit where all agreed that Taurus-Littrow could be the selected site. Thus, in late February 1972, only 9 months from launch, Taurus-Littrow was approved as the exploration site for Apollo 17. The Valley of Taurus-Littrow offered four major benefits as the last Apollo landing site, taken in the context of a final test of then current hypotheses related to the origin and evolution of the Moon. First, photogeologic analysis indicated that Taurus-Littrow provided access to a three-dimensional window into a mountain ring created by the Serenitatis large basin-forming event, by now well established as the result of a giant impact of an asteroid or comet. Second, major units of mare basalt and older nonmare rocks would be within easy reach of roving vehicle traverses. Third, a mantle of dark, possibly young volcanic debris partially covered the region as well as portions of the valley, and craters of a range of depths penetrated this debris and the underlying basalt. And, fourth, the valley lies about 600 km north and 200 km east of the Apollo 11 and Apollo 15 sample areas, respectively, adding significantly to our exploration coverage of the Moon's nearside. Due to the foreknowledge that Apollo 17 would be the last of the Apollo series, selection of its landing site became a contentious issue among lunar scientists and between lunar scientists and operational planners. Impact cratering, origin and evolution of the Moon were subjects of Apollo 17's scientific informers and enquiries and are discussed. Keywords: Apollo 17; Moon; mission; impact cratering; origin; Lunar evolution; Lunar craters; Magma Ocean; cratered highlands; basins; geologic events; implications