“It’s remarkable to think that the samples Apollo 16 brought back more than half a century ago still have secrets to reveal about the moon’s history,” said Mark Nottingham, author of a landmark paper on lunar samples. These are the words that capture the wonder and scientific curiosity behind lunar exploration today. The Apollo 16 mission that flew in 1972 brought back not only dust and stones, but a moon time capsule of the violent past a past that had been shaped by asteroid impacts, solar bursts, and the unforgiving space weather forces.
The Descartes highlands area of the moon from which Apollo 16 crew members John Young, Charles Duke, and Ken Mattingly returned close to 200 pounds of material is a gold mine of geological history. New studies of the samples found evidence of the occurrence of noble gases such as argon and xenon trapped in regolith breccias rock structures that were formed due to the tremendous pressure of asteroid collisions. They are cosmic dates that allow scientists to peer back into the ages of the surface exposure on the moon, from 2.5 billion years to less than a billion. This broad range informs scientists the lunar regolith that covers the surface in the area is “well mixed,” with older regolith buried under more recent impacts.
The ramifications of this finding are enormous. Nottingham and colleagues at the University of Glasgow used sophisticated mass spectrometry methods to measure the abundance of noble gases in the samples. “We can build a much more complete picture of the history of this part of the moon during the early solar system,” Nottingham said. The research suggests that in the first billion years of the moon’s existence, asteroid impacts were larger and more prevalent, slowing down approximately two billion years ago. Not only does this timeline contribute to our knowledge of lunar evolution, but it also falls into accordance with trends elsewhere within the solar system.
The moon, sometimes perceived as Earth’s tranquil companion, holds secrets of our own history. Scientists have always appreciated the fact that the moon’s surface is an unbroken record of asteroid impacts. In contrast to Earth, where tectonic activity, water, and wind progressively fill in impact craters over time, the moon’s craters are preserved. A new study with NASA’s Lunar Reconnaissance Orbiter (LRO) discovered that asteroid impacts doubled or tripled some 290 million years ago, a finding that upends previous theories of Earth’s impact rate.
These results are revolutionizing lunar science in new ways. Scientists long thought some of the Moon rocks brought back on Apollo missions were “pristine,” unscathed by impact. Proved them wrong has a team led by Arizona State University. Scientists applied a new technique of aluminum-in-zircon analysis to find that the crystals in the samples did not originate with the material they were embedded in. They are very intricate blends, the result of multiple effects. “This means what we thought were untouched igneous rocks are complex mixtures,” said lead author Melanie Barboni.
These findings make it more important than ever to reanalyze Apollo samples with new technology. Two years back, NASA cracked open one of the final sealed samples from Apollo 17 using new instruments to pull out information that had previously been inaccessible. These missions aren’t merely learning about the moon’s past; they’re gearing it up for its future. Finding noble gases and other compounds in lunar regolith will provide insight to future crewed missions in determining materials required for creating sustainable bases on the moon a possibility.
The samples from Apollo 16 also provide insight into lunar geologic history. Scientists found two prevailing groups of regolith breccias at the landing site: an “ancient” group that had formed between 3.8 and 3.4 billion years ago, and a “younger” group that had formed between 2.5 and 1.7 billion years ago. A third one, so-called soil-like breccias, is thought to have formed in the last two billion years. These groups provide a glimpse of the history of the moon from an age of massive basin-forming impacts to one of more subdued times with smaller asteroid impacts.
As human evolution gears up to return to the moon, these scientific papers are more than that. They’re exploration road maps, guiding lander, habitat and resource extractor development. “Understanding the lunar surface is critical to revealing the history of the solar system,” says Noah Petro, a project scientist at NASA’s LRO. His words sound the familiar and enduring refrain of the Apollo flights, which keep informing our cosmos.
The history of the moon is not fixed, but living; it’s a dynamic history inscribed on dust and rock, ready to be deciphered. With each new research, scientists are not only revealing secrets of the moon but are rewriting the solar system’s history, sample by sample.
