Moon's mighty magnetic field was a 5,000-year titanium blip

"Our new study suggests that the Apollo samples are biased to extremely rare events that lasted a few thousand years - but up to now, these have been interpreted as representing 0.5 billion years of lunar history. It now seems that a sampling bias prevented us from realizing how short and rare these strong magnetism events were."

"The study argues that the formation of high-titanium rocks and a strong lunar magnetic field were the result of titanium-rich material melting deep inside the Moon, which created a strong magnetic field, but only for about 5,000 years."

"We now believe that for the vast majority of the Moon's history, its magnetic field has been weak, which is consistent with our understanding of dynamo theory. But that for very short periods of time - possibly as short as a few decades - melting of titanium-rich rocks at the Moon's core-mantle boundary resulted in strong magnetism."

Oxford scientists resolved a decades-long debate about the Moon's magnetic field by analyzing lunar rock composition. Apollo samples showed evidence of a strong magnetic field, contradicting theory that the Moon's small core couldn't generate one. Researchers discovered that high-titanium basalt rocks correlate with strong magnetism. These rocks formed during brief periods when titanium-rich material melted at the Moon's core-mantle boundary, creating intense magnetic fields lasting only thousands of years. Previous interpretations mistakenly attributed these rare, short-duration events to represent half a billion years of lunar history. The Moon's magnetic field was actually weak throughout most of its history, consistent with dynamo theory predictions.

Read at Theregister