It may come as a surprise that glass is found widely on the surface of the Moon. Such glass is not the kind found in windows or bottles, but tiny, dust-like beads formed in violent volcanic eruptions billions of years ago. When the Apollo astronauts returned to Earth in the 1970s, they brought back lunar samples that told a remarkable story. Unlike Earth, with its shifting tectonic plates, the Moon’s crust has remained relatively stable for eons. Its ancient volcanoes, lava plains and pyroclastic rocks are still there, frozen in time – a visible record of a fiery past.
Those volcanoes are also where the glass originally came from. Under the moon’s extreme conditions, magma ejected by volcanoes billions of years ago cooled swiftly during the few minutes it was in flight, losing its water and internal gases such as sulfur, chlorine and fluorine along the way. Scientists used to think that this was the end of the story, the beads lost all of their gas, landed as inert glass and remained unchanged ever since.
A new “breathing” discovery
But a new CUHK-UCLA co-led study suggests otherwise. The research indicates that the beads lost only a small amount of their gas during flight. Once buried beneath the new eruptive material, they were insulated from the extreme cold of space. Shielded in this way, the beads cooled slowly rather than instantaneously, allowing them to continue releasing gases over extended periods.
The research team examined glass beads from sample 74220, collected during the Apollo 17 mission in 1972 and dating back about 3.64 billion years. Using advanced analytical techniques, they were able to trace their life history from deep inside the Moon to their eventual cooling on the surface. Professor Zhan Yan from CUHK’s Department of Earth and Environmental Sciences said: “We started by gathering volatile measurements from three types of specimens in sample 74220. We then built an improved diffusion model that included a realistic cooling curve instead of assuming a constant temperature, and required a single cooling history to explain all four gases at once.”
The research shows that free-flight cooling alone simply couldn’t account for the observed gas loss. The team built a thermal model showing that beads buried under insulating volcanic dust could stay warm for years. Putting all the evidence together, the research proposes a three-stage degassing history: ascent from the lunar interior, brief flight through the vacuum of space, and slow, prolonged cooling after landing.
A window into the lunar interior
These discoveries offer more than a revised timeline – they open a new window into the Moon’s inner composition. Because the beads come from deep inside the Moon, they can provide important information about the substances contained within it – but only if scientists can accurately determine when those substances were released during cooling, which this study provides the framework.
Professor Ni Peng from the Department of Earth, Planets and Space Sciences at UCLA said: “The beads kept hold of most of their gas when they landed. The free-flight phase lasted only about a few hundred seconds – not long enough for much of the volatile content to diffuse out from the interior. The dramatic gas losses that show up in the lab today – about 98-99.9% for water, 70-90% for chlorine and 40-70% for fluorine – only reached those levels after the beads sat buried under insulating volcanic dust for roughly three years, slowly releasing their gases.”
In fact, buried about 30cm beneath the surface, the beads took more than a decade to reach ambient lunar temperatures. The regolith, it transpires, “is an extraordinarily good insulator in the Moon’s vacuum, since there’s no air or water in the pores to help carry heat away”, said Professor Ni.
Rethinking a “breathless” world
“Our results suggest the Moon’s volatile cycle has been more active and more drawn-out than previously assumed. Even a ‘dead’ world like the Moon, it turns out, may have spent long stretches of its history slowly breathing.”
The team’s findings could also refine our understanding of how water forms and is preserved on the Moon.
Professor Zhan said: “The traditional thinking emphasised external sources – comet impacts, asteroid deliveries and solar wind interactions – as the main suppliers of polar ice. Our study adds a homegrown contribution to that picture: the Moon’s own volcanic deposits, slowly leaking gas for years after each eruption, would have continuously fed volatiles into the tenuous lunar exosphere.”
“Once those gases escape into space above a deposit, individual molecules bounce across the lunar surface in long, random hops. Most are eventually lost, but a small fraction happens to land in the deep, frigid shadows of polar craters where temperatures are so low that water, sulphur compounds and chlorides freeze on contact and become trapped indefinitely. Over billions of years and many eruption cycles, even a slow trickle of volcanic vapour could add up to a meaningful contribution to the ice now sitting at the poles.”
A new perspective on the Moon
What emerges from this research is a subtle but profound shift in how we understand the Moon. No longer merely a static, dead body, it appears instead as a world with a long, lingering internal rhythm – one in which ancient eruptions continued to shape its environment long after the lava cooled.
The humble glass bead, once dismissed as a frozen remnant, now offers a rare window into this hidden history.
And as scientists continue to unlock its secrets, the Moon – silent as it may seem – is telling us that it has been anything but.