The moon was once a hive of volcanic activity. But while the vents have remained inactive and dormant for tens of millions of years or more, the satellite retains evidence of its once volatile past – evidence that includes caves, plains, and teeny tiny glass beads that glisten and shimmer on the moon’s rocky surface.
Ryan Ogliore, an associate professor of physics in Arts & Sciences at Washington University in St. Louis, described the beads as “some of the most amazing extraterrestrial samples we have.” Explaining their significance in a press release, he said, "The beads are tiny, pristine capsules of the lunar interior."
While they vary in color – some are a dazzling orange, others are jet black and shiny – all are one millimeter or less and would have been forged from the magma of lunar volcanoes.
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The Moon's Volcanic Past
The beads were collected by astronauts on the Apollo mission more than 50 years ago. Yet, it is only now, thanks to modern technology, that researchers have been able to analyze the chemical composition of the samples and delve more deeply into the moon’s volcanic past.
"Many of these instruments would have been unimaginable when the beads were first collected,” said Ogliore in the press release.
The team, writing in the journal Icarus, employed a combination of techniques and technologies, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, atom probe tomography, and transmission electron microscopy.
Before the analysis took place, small samples of material were separated using a high-energy ion beam. Crucially, the researchers used samples that had never been exposed to oxygen and other elements in the Earth’s atmosphere, which could react with minerals on the beads' surface and taint the results. To ensure they remained pure and pristine throughout the research, the team used air-free transfer shuttles to move the material between different pieces of equipment.
Unravelling the Moon’s History
The researchers explain that the beads would have formed during volcanic eruptions some 3.3 billion to 3.6 billion years ago, when molten rock ejected from the vent solidified instantaneously due to the cold temperatures on the moon’s surface. While the deposits mainly comprise of nanopolycrystalline sphalerite (Zn, Fe)S) – a mineral consisting of zinc, iron, and sulfur – the differences in color of individual beads reveal how volcanic activity changed over time.
Due to their cosmic origins, the beads are unique to anything produced on this planet, but Ogliore explains there are earthly comparisons to be made.
"The very existence of these beads tells us the moon had explosive eruptions, something like the fire fountains you can see in Hawaii today," said Ogliore in the press release. He describes the results of the analysis as "like reading the journal of an ancient lunar volcanologist."
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Rosie McCall is a freelance writer living in London. She has covered science and health topics for publications, including IFLScience, Newsweek, and Health.
