Ancient asteroids deposited water into the molten moon

While much recent research has focused on the role of comets in introducing water and the basic elements of life to Earth, a new study appearing in the latest issue of Nature Communication has revealed that H2O buried deep in the moon comes from a different source – asteroids.

In the paper, Dr. Jessica Barnes from the Open University in the UK and her colleagues analyzed the chemistry of rock samples obtained by the Apollo missions and compared their findings with the composition of other types of space rocks, according to BBC News reports.

Their results indicated water was most likely delivered to the moon, which would have still been molten at the time, by asteroids approximately 4.5 to 4.3 billion years ago, the Los Angeles Times added. The cooling magma would have prevented water from escaping, and volcanic activity occurring much later likely caused some of it to find its way back to the lunar surface.

When the Apollo astronauts reached the moon, they collected rocks containing trace amounts of water (between 10 and 300 parts per million), Dr. Barnes told BBC News. Past research found the molecular signatures of moon rocks were similar to those of the water-rich carbonaceous chondrite meteorites that occasionally find their way from the asteroid belt to the Earth.


These impacts happened when the Moon was mostly molten rock. Credit: NASA

Did the Earth get its water in the same way?

Now, Dr. Barnes and colleagues from the US and France conducted a series of simulations that found that, to achieve the chemistry of the water found on the moon, only a fraction of that H2O could have come from comets, as comets tend to have “heavier” water filled with the hydrogen isotope deuterium. They concluded that most of the water had to have come from asteroids.

These asteroids, the study authors explained, would have been extremely similar to carbonaceous chondrites and likely pelted the moon during its first 200 million years of existence. Based on the data, they believe that 80 percent of the lunar water was introduced there by asteroids, while only 20 percent had cometary origins – and due to the proximity of the moon to the Earth, particularly during this time, our planet’s water may have come from similar sources.

“We think that asteroids delivered water to the interior of the Moon, by in a crude sense, smashing into it,” Dr. Barnes explained to the Daily Mail. “This had to happen very early on in the moon’s history, in order to account for water that is present in very old samples that were derived from the interior of the moon. We believe this addition of water happened during the first 10 to 200 million years of its history, when the lunar magma ocean was present.”

She added that “there is still a lot we do not yet fully understand about the water and other volatiles in the moon and how they relate to each other, specifically the processes that might alter the abundances of volatiles in lunar magmas,” and told the UK newspaper that these topics are things that she plans to investigate during the months and years ahead.


Image credit: NASA