Moon’s Ancient Magnetic Field May Have Flickered On and Off

sciencehabit quotes a report from Science Magazine: For decades, planetary scientists have pored over a mystery hidden within the Moon rocks retrieved by Apollo astronauts in the 1960s and ’70s. Minerals in the rocks record the imprint of a magnetic field, nearly as powerful as Earth’s, that existed more than 3.5 billion years ago and seemed to persist for millions of years. But generating a magnetic field requires a dynamo — a churning, molten core — and most researchers believed the Moon’s tiny core would have long since cooled off, 1 billion years after it formed. Corroborating that picture are other ancient Moon rocks of about the same age that suggest the field was weak — leaving planetary scientists baffled.

Now, researchers are proposing a new way to solve the puzzle. A paper published today in Nature Geoscience theorizes that between 3.5 billion and 4 billion years ago, blobs of titanium-rich magma melted episodically just above the core, rising in plumes that drove volcanic eruptions on the surface. By intermittently stirring up the Moon’s core, these bouts of melting would have caused the Moon’s magnetic field to flicker on in short, powerful bursts. The paper “links a few different concepts that people were thinking about separately, but hadn’t actually brought together,” says Sonia Tikoo, a planetary geophysicist at Stanford University who was not involved in the study.