The moon may have been volcanically active more recently than we thought. Analysis of lunar material brought back by China’s Chang’e 5 spacecraft has shown that the magmatic rocks where it landed are less than 2 billion years old, indicating that the history of the moon is more complicated than researchers realised.
The region where Chang’e 5 touched down, called Oceanus Procellarum, was expected to contain relatively fresh rocks, but we didn’t know just how fresh. Researchers analysed two small samples the mission returned and found that they solidified from lava 1.96 billion years ago.
“There would have been magma being thrown up tens to hundreds of metres [above the surface] like a fountain,” says at the University of Manchester in the UK, who was part of the research team. “It would have then puddled on the ground and flowed like runny motor oil and spread for kilometres around the eruption site.” This happened long after many models of the moon’s evolution suggested its volcanic activity should have been over.
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These samples also had slightly different compositions than other moon rocks we have analysed, with more iron and less magnesium. “This indicates that the lunar interior is more complex and heterogenous than we have anticipated,” says at Curtin University in Australia, also part of the team.
One possible explanation for the late volcanism is that radioactive elements inside the moon kept it hot for far longer than we expected. “However, the chemistry of the fragments we have analysed does not match this idea very well,” says Nemchin. “It all has to be tested with further analyses of more fragments, but if that is the case, we would have to rethink our views related to a substantial part of lunar history.”
The other potential solution is the idea that when the moon was closer to Earth billions of years ago, the gravity of our planet could have stretched the moon and heated its interior. “Much as the moon influences our tides on Earth, our planet could influence the mantle and deeper areas on the moon,” says Joy. “The moon could have stretched and flexed back and forth, and that could have caused some melting.” There are other teams working with other fragments of the samples from Chang’e 5, so those results might help illuminate how these strange, young rocks formed, she says.
Science
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