At the time of writing this, December 1972 was the last time a human walked on the surface of another planetary body. The Apollo 17 mission launched on December 7th 1972, with crew members Eugene Cernan, Ronald Evans and Harrison ‘Jack’ Schmitt. The lunar module (carrying Cernan and Schmitt) landed on the Moon 4 days later, and all three returned to Earth on December 19th – in time for Christmas!
The complexity of the Apollo missions increased throughout the programme. Starting with a series of uncrewed flights of the Saturn V launch vehicle (so-called “A-type” missions), through to the Apollo 11 initial lunar landing mission (“G-type”) in July 1969, precision landing and systematic exploration with Apollo 12 and 14 (“H-type”), and culminating in the Apollo 15, 16 and 17 missions (“J-type”). These “J-type” missions carried out the most extensive scientific investigation of the Moon during the programme. This was made possible by the significantly longer distances covered by the astronauts due to the use of the Lunar Roving Vehicles. Besides being the final Apollo mission, Apollo 17 is notable for the heavy emphasis on science and the inclusion of a geologist on the crew (Jack Schmitt).
Apollo 17 landed in the Taurus-Littrow region of the Moon, just south east of the Mare Serenitatis. The complexity of the local geology was a driving force behind the site selection. At the time, the Taurus-Littrow valley was deemed to provide one of the best chances to study a combination of different rock types, including ancient lunar highlands material (i.e. what are thought to be the first rocks to form on the Moon) and basaltic rocks younger than those collected at the previous Apollo landing sites (i.e. less than about 3 billion years old). Located on the eastern edge of the Serenitatis impact basin, it was also hoped that the Apollo 17 landing site could provide an opportunity to investigate the timing of large impact basin formation. Earlier photogeological mapping had indicated that ejecta from the Crisium and Imbrium impact basins would also be present in the vicinity, in addition to that Serenitatis.
As with all the Apollo missions, we are still learning new things from the rocks collected, even half a century on. My own research has involved studying both the basaltic and impact-generated rocks from Apollo 17. Together with colleagues at the Swedish Museum of Natural History, we obtained new precise ages for the basaltic rocks erupted onto the surface of the Taurus-Littrow valley. Contrary to the initial expectations of the mission planners, and compared to those collected by the other Apollo missions, the Apollo 17 basalts are actually amongst the oldest “mare” basalts (the term used to describe the large expanses basalts particularly on the lunar near side – i.e. the dark bits you can see on the Moon). We now know that the Apollo 17 basalts were formed over a fairly narrow time interval (in lunar geology terms!) of 3750-3770 million years ago. Meanwhile, our analyses of Apollo 17 impact breccias have helped better constrain the timing of the formation of the Imbrium basin forming impact. Together with samples from another 4 of the Apollo landing sites (12, 14, 15 and 16), this impact appears to have occurred 3922 million years ago (±12 million years).
Given the complexity of the landing site and the samples, there is undoubtedly still a lot to learn from Apollo 17. For example, the Apollo 17 astronaut, Jack Schmitt, is continuing to study the geology of the site, looking at determining the origins of boulders that he and Eugene Cernan sampled. Using high-resolution satellite images, he and his colleagues have been able to trace the trails these boulders left as they rolled down the surrounding hills from the surrounding cliffs.
Perhaps most exciting for those of us who study lunar samples is the Apollo Next Generation Sample Analysis (ANGSA) initiative. During the Apollo programme, it was decided that some of the returned rocks would be kept in untouched in a separate storage facility, in order to provide pristine samples for future analytical methods. This includes an Apollo 17 “drive tube” sample, which has just been opened and is now being studied!
References:
Nemchin et al. (2021) Ages of lunar impact breccias: Limits for timing of the Imbrium impact. Geochemistry 81:125683. https://doi.org/10.1016/j.chemer.2020.125683
Schmitt et al. (2017) Revisiting the field geology of Taurus–Littrow. Icarus 298:2-33. https://doi.org/10.1016/j.icarus.2016.11.042
Snape et al. (2019) The timing of basaltic volcanism at the Apollo landing sites. Geochimica et Cosmochimica Acta 266:29-53. https://doi.org/10.1016/j.gca.2019.07.042
Thiessen et al. (2017) Impact history of the Apollo 17 landing site revealed by U-Pb SIMS ages. Meteoritics and Planetary Science 52:584-611. https://doi.org/10.1111/maps.12814
Earth & Solar System 