Apollo 16 astronauts John Young, Charles Duke, and Ken Mattingly brought over 95 kg of samples back to Earth in 1972. Among these were "regolith breccias," which form when lunar soil, or regolith, is fused by asteroid impacts. These rocks preserve the geochemical makeup of the Moon's surface at the time of their formation, offering critical clues about lunar history.
The research, conducted by a team from the UK and USA, and published in the journal 'Meteoritics and Planetary Science', used mass spectrometry to analyze gases trapped in smaller chip samples, known as "soil-like breccias." These samples had never undergone such detailed analysis before. Dr. Mark Nottingham, the study's lead author, explained, "Mass spectrometry can help us determine how much time the samples spent exposed on or near the Moon's surface. That helps give us a clearer idea of the history of impacts on this particular area of the Moon."
The findings reveal new insights into how solar wind and asteroid impacts have altered the lunar surface over billions of years. "Over the course of the samples' time on the surface of the Moon as regolith, they were exposed to varying amounts of solar wind... which built up on the outer layers of their mineral grains for millions of years before they were struck by an asteroid," said Dr. Nottingham.
The study provides crucial details on the Moon's history, which parallels Earth's own history of asteroid bombardment. Unlike Earth, however, the Moon's surface has remained geologically inactive, preserving these records as time capsules. "The Moon's history is locked in geological time capsules... which allows us to use cutting-edge technology like mass spectrometry to unlock their secrets," Dr. Nottingham added.
The research could also benefit future lunar missions, including NASA's Artemis program, by identifying natural resources that could help support long-term human habitation. Previous studies separated the Apollo 16 breccias into ancient (3.8 to 2.4 billion years old) and younger (2.5 to 1.7 billion years old) samples, but the new analysis showed a wide range of exposure ages, suggesting complex impact histories.
NASA provided the researchers with 11 Moon samples, nine of which showed varying exposure ages from 2.5 billion years to less than a billion. This indicates that these samples were formed in areas with diverse impact histories. Two samples had much lower concentrations of noble gases, suggesting they were formed more recently, possibly linked to the South Ray crater.
Dr. Nottingham noted that this is the first time soil-like breccias have been categorized as a distinct group with unique histories. "We can build a much more complete picture of the history of this part of the Moon during the early solar system," he said.
The research offers valuable knowledge that could inform future exploration efforts. "Studies like this add to our knowledge base about where useful elements like noble gases can be found in the lunar regolith, and how abundant they might be," Dr. Nottingham said.
Researchers from NASA Goddard Space Flight Centre, the Catholic University of America, and Birkbeck College, London, also contributed to the study.
Research Report:Constraints on the Impact History of the Apollo 16 landing site: Implications of Soil-like Breccia noble gas records
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