Cartier reports that July 20, 1969 will forever be carved into the history books: the day that humankind took its first small step into the cosmos. The dawn of a new scientific era came just 4 days later. When Apollo 11 splashed down on 24 July, planetary scientists knew they would soon get their hands on the first samples of material brought back from the surface of the Moon. Apollo 11 astronaut Neil Armstrong collected a contingency sample of the lunar surface just after taking the first steps on the Moon. He stored the sample in his pocket in case they needed to make a quick departure. Apollo 11 astronauts brought back a scant 22 kilograms of material for scientists to study. Each subsequent Apollo mission—except Apollo 13, of course—brought back more and more rocks, soil samples, and drill cores. All told, the Apollo astronauts carried back to Earth 382 kilograms from six different areas of the Moon’s surface, each sample stored in a container that preserved a Moon-like environment.
The earliest looks at the Apollo samples proved for the first time some facts about the Moon that may seem obvious today: There is not now and there likely never has been life on the Moon, meteor impacts throughout the Moon’s history have pulverized the surface, and the Moon and Earth share many geochemical similarities. But technology, computer power, and scientific knowledge have grown exponentially since humans last stepped foot on the Moon in 1972. Thanks to the foresight of NASA leaders of the time, some of the Apollo samples were curated so that future scientists could study pieces of the Moon that hadn’t been exposed to Earth’s atmosphere. “What we like to say is that sample return missions allow scientists not yet born to use instruments not yet developed to answer questions not yet asked,” Jamie Elsila, an astrochemist at NASA Goddard Space Flight Center in Greenbelt, Md., told Eos.
Today, “we’re asking some of the same questions that the scientists back then were asking,” Elsila said. “Because [NASA] preserved these samples and curated them carefully, now we’re able to go back and try to answer these questions.” As post-Apollo scientists studied carefully doled out lunar samples, they discovered much more about the Moon and its history than scientists of the 1970s could have. Here are some of the most notable discoveries about our celestial neighbor that have come from Apollo samples over the past 50 years.
Life as a soil grain on the lunar surface is tough. Nowadays, it’s rare for a large impact to happen on the Moon, but microscopic impacts happen all the time. “The lunar regolith is being bombarded by micrometeorites and high-energy particles from the solar wind,” explained Richard Walroth, an instrument developer at NASA Ames Research Center in Mountain View, Calif.
Earth’s atmosphere protects its surface from these microscopic hits. On the airless Moon, however, tiny meteorites, cosmic rays, and superfast ions from the Sun constantly strike the surface. This process, called space weathering, makes the lunar regolith literally rough around the edges. “The grains melt at the very edge and form things called agglutinates,” Walroth said, which are mineral fragments fused together by glass. “They also get a little nanophase iron too. They’re like nanoscale droplets, essentially of metallic iron in glass.” Walroth and his team have developed instruments to look at the mineralogy and weathering of agglutinates and other Apollo samples.
Apollo 17 astronaut Harrison Schmitt collected samples of lunar regolith beneath the shadows of large boulders. The boulders partially shielded the regolith from micrometeorite impacts and some of the effects of space weathering. The samples returned by Apollo astronauts bear the scars of space weathering, but some of the regolith samples were shielded from one type of weathering for millions of years.
“Shadowed soils…were collected at the surface but underneath the overhangs of boulders,” said Barbara Cohen, a planetary scientist at NASA Goddard Space Flight Center. “In that case, we think that they were shadowed from things like micrometeorite impacts, but they were still exposed sometimes over seasonal and day-and-night cycles to things like solar wind.” “They might have a different total exposure history” than soils that were exposed to all types of space weathering processes, Cohen said. Comparing soils collected in different places will help Cohen and her team tease out which processes cause the different weathering signatures they see in Apollo samples.
“Space weathering is a global process,” Walroth said, but “every part of the Moon’s going to get affected by it a little bit differently.”
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