Nasa turns to the Moon to solve a mystery about water on Earth

The study was led by Tony Gargano, a postdoctoral researcher at Nasa’s Johnson Space Center and the Lunar and Planetary Institute in Houston. Gargano and his team used an innovative technique to analyse lunar regolith, the dusty, rocky layer that blankets the Moon’s surface. Unlike Earth, whose weather patterns, erosion, and geological processes are constantly changing its surface, the Moon has retained the history of the events that have remained unchanged for billions of years. The Moon is therefore an important resource for information about the impacts that have affected the Moon and Earth.

Earlier studies of lunar soil relied heavily on metal-loving elements to track meteorite material. But repeated impacts can mix and alter those elements, making it difficult to identify their original sources. To get around this problem, Gargano’s team used triple oxygen isotopes, which are like a chemical fingerprint. Oxygen is the most abundant element in rocks and is not affected by high-energy impacts, giving a much clearer indication of what type of meteorites impacted the Moon.

The data showed that at least one per cent of the lunar regolith contains material from carbon-rich meteorites, which are known to contain water. Based on this information, the team was able to estimate the amount of water that the meteorites could have delivered. Even when they applied generous assumptions and scaled the results to reflect Earth’s much higher impact rate, the total water contribution turned out to be only a small fraction of what fills Earth’s oceans today.

“Our findings don’t mean meteorites brought no water at all,” said Justin Simon, a co-author of the study and planetary scientist at NASA Johnson. “They say the Moon’s long-term record makes it very hard for late meteorite delivery to be the dominant source of Earth’s oceans.”

While the amount of water delivered to Earth appears minimal, the findings are still important for understanding the Moon itself. Over billions of years, even small deliveries of water could matter for the Moon, where accessible water is mainly trapped in permanently shadowed regions near the poles. These icy pockets are of great interest as Nasa prepares for future human missions under the Artemis programme.

All of the samples used in the study came from Apollo landing sites near the Moon’s equator on the side facing Earth. Though collected more than five decades ago, they continue to produce new discoveries. Scientists are hopeful that future samples returned by Artemis astronauts will provide an even broader view of the Moon’s history and deepen our understanding of how water and other essential materials shaped the inner solar system.