- The moon’s surface is covered in dry regolith, fragmented rocky material. Some of the regolith is composed of a type of rock called breccia.
- Some of the breccia samples are unique and “soil-like,” according to a new study using samples from 1972, brought back to Earth in the Apollo 16 mission.
- The breccia samples provide clues to the moon’s history. This includes how the surface has changed over billions of years from meteoroid and asteroid impacts, as well as the solar wind from the sun.
Like Earth, our moon is at least 4.5 billion years old. But the moon doesn’t have an atmosphere or plate tectonics. So there’s no wind or rain to erode the surface, and no shifting of land plates to alter the landscape. Still, the moon’s surface has changed over time. In a new study, researchers in the U.S. and U.K. analyzed lunar regolith collected by Apollo 16 astronauts more than 50 years ago. The researchers said on October 21, 2024, that these rocks are like “time capsules.” They provide clues to the moon’s past and present.
The researchers focused on lunar breccias – a type of sedimentary rock – from the regolith. They published their peer-reviewed findings in the journal Meteoritics and Planetary Science on October 15, 2024.
The complex history of the moon
With no wind, weather or tectonics, the moon looks like a simple world to study, with its gray dust and ubiquitous craters. But its history is complicated, just as Earth’s is. The craters are the result of collisions with debris in space – some of which we now call asteroids – primarily from a time after the moon first formed. The moon’s surface is saturated with craters, which makes it difficult for scientists to determine exactly what happened when.
Some of the rock samples the astronauts brought back to Earth were breccias, which tend to be composed of large angular fragments with spaces between. The spaces of the rock are filled with smaller particles and a type of mineral “cement” that binds the rock together.
On the moon, these rocks formed when meteoroid and asteroid impacts heated and fused lunar dust (regolith) into rock.
Analyzing breccia samples
The researchers analyzed 11 breccia samples altogether. None of these had been studied before. They were part of more than 95 kg (209 lbs) of rock samples that astronauts John Young, Charles Duke and Ken Mattingly brought back to Earth in 1972.
The scientists used sophisticated analytical mass spectrometry techniques to analyze the samples. They wanted to study the makeup of gases trapped in some of the smaller chip samples, called “soil-like breccias.” (To note, the moon has dry dusty regolith, not soil as we know it.) In mass spectrometry, chemical substances are identified by the sorting of gaseous ions in electric and magnetic fields according to their mass-to-charge ratios.
Mark Nottingham led the research while he was at the University of Manchester in the U.K. He is now at the University of Glasgow’s School of Geographical & Earth Sciences. He said:
Mass spectrometry, which identifies molecules in samples and quantifies their relative abundance, 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.
Nine of the samples showed exposures from 2.5 billion years ago to less than a billion. This indicated that the regolith in that area resulted from a varied history of impacts. Some of the samples had been buried, but brought to the surface by the impacts. But other samples had been on the surface and exposed to the solar wind for billions of years.
Samples collected from the surface of the Moon by the crew of Apollo 16 more than 50 years ago have helped scientists at @UofGGES reconstruct billions of years of lunar history.
Read more here: pic.twitter.com/BUA5qEosQR
— UofG News (@UofGNews) October 21, 2024
Soil-like breccias are unique
The analysis showed that the soil-like breccias are distinct from the other breccia samples. As Nottingham explained:
This study establishes for the first time that soil-like breccias are their own distinct category, with their own histories to share. Combined with analysis of the ancient and young rocks recovered by Apollo 16, we can build a much more complete picture of the history of this part of the moon during the early solar system, where heavier impacts on the lunar surface in its first billion years or so gave way to less intense periods from two billion years ago or so.
Two of the samples also contained lower amounts of noble gases than usual as well. These are seven chemical elements that make up Group 18 (VIIIa) of the periodic table. This suggests the samples formed much more recently and were exposed to the solar wind for less than a million years. The research team even pinpointed the possible source of the samples as the nearby South Ray crater.
‘Time capsule’ moon samples
The “time capsule” samples provide new clues about how the moon’s surface has changed over billions of years. Those changes come not only from asteroid impacts, but also the solar wind, as Nottingham noted:
Over the course of the samples’ time on the surface of the moon as regolith, they were exposed to varying amounts of solar wind – charged particles flowing from the sun which also carry traces of noble gases like argon and xenon – which built up on the outer layers of their mineral grains for millions of years before they were struck by an asteroid.
The samples also help scientists better understand the history of Earth and other rocky bodies in the solar system. Nottingham continued:
The moon’s history is the Earth’s history too; the record of asteroid bombardments etched on its face and under its surface can help us understand the conditions of the early solar system which formed our planet as well as its closest neighbor.
Unlike the Earth, however, the moon’s history is locked in geological time capsules on its surface, untouched by plate tectonics or erosion, which allows us to use cutting-edge technology like mass spectrometry to unlock their secrets.
Natural resources and future missions
The samples not only provide new insights into the moon’s history. They can also help scientists plan for future human missions back to the moon, and even beyond, in terms of natural resources. Nottingham said:
One of the challenges of establishing long-term habitats for humans on the moon is making decisions about how we can use the natural resources which await future missions so they don’t have to carry everything they’ll need with them from Earth.
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.
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, and that they could yet help shape how we explore the solar system in the decades to come.
Bottom line: A new analysis of “time capsule” moon samples brought back to Earth by Apollo 16 shows how the surface of the moon has changed over billions of years.
Source: Constraints on the impact history of the Apollo 16 landing site: Implications of soil-like breccia noble gas records
Via University of Glasgow
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