The Apollo experiments
On 11 December 1972, the sixth and final lunar surface mission of the Apollo Program (Apollo 17) landed in a valley near the edge of Mare Serenitatis. Astronauts Eugene Cernan and Harrison Schmitt spent 72 hours at the site, named Taurus-Littrow. The site was geologically diverse, with the mountain ring of the Serenitatis Basin nearby, and lava filling in the valley lowlands. The main objective of the mission was to collect samples of these different types of rock.
Figure 1.2.
Apollo landing sites.
The crew spent more than 22 hours on the lunar surface, using the rover to traverse the mare plains. The traverses totaled more than 30 km, and nearly 120 kg of rock and soil were collected - the largest total sample mass of any Apollo mission. Many of the rock samples have since been studied in detail. A mass spectrometer was placed on the lunar surface during the Apollo 17 mission. It provided data on the distribution of many types of rarefied gases, including argon-40 and helium-4, and very small amounts of argon-36, methane, ammonia, and carbon dioxide at sunrise, as well as neon-20, neon-22, and molecular hydrogen.
Essentially, all the argon-40 on the Moon comes from the decay of potassium-40 in the lunar interior. Variability in the amount of atmospheric argon (a 6 to 7 month periodicity was observed) suggests the presence of a partially molten core, which is interesting from both scientific and resource utilization standpoints. If deep vents that periodically release gases onto the surface are found, these gases could be trapped and used for manufacturing, as carrier gases in pneumatic conveyor systems, and for other uses.
A similar instrument, the supra-thermal ion detector, had, on an earlier mission, documented the presence of a cloud of hot solar-wind electrons near the terminator. This cloud was found to vary with changes in the solar wind and extreme ultraviolet flux. In addition, one other interesting event was found. This event, principally water vapor, must remain suspect because of its proximity to the Apollo 14 mission.
However, the large magnitude and the long time duration of the event argue against a mission-related source.
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