Scientists say that “extremely rare events” associated with the landing area of NASA’s Apollo missions have led to decades of wrong assumptions about the strength of the Moon’s magnetic field, fueling a long-standing debate that Oxford researchers say they have finally settled.
The Moon’s early magnetic field, between 3.5 and 4 billion years ago, has long puzzled scientists, who have argued over how strong it could have been. Now, a new paper in Nature Geoscience suggests that both sides of the debate may be correct, due to the unusual nature of the Apollo landing sites and misinterpretation of data from lunar rock samples collected by astronauts in the 1960s and 1970s.
Reconsidering the Apollo Moon Samples
One major argument against a strong lunar magnetic field is the Moon’s relatively small core, which is only about one-seventh of its radius. Based on this, scientists have long expected the Moon’s magnetic field to be weak, if it existed at all. Yet strong magnetism has been detected in rocks returned by the Apollo missions, implying the Moon once possessed a far more powerful field than it does today.
The new research reconciles this contradiction by proposing that the Moon produced strong magnetic fields only during brief episodes.
After analyzing decades-old Apollo samples, researchers determined that the Moon’s magnetic field occasionally surged in intensity. For most of its history, the Moon likely maintained a weak field, as scientists would expect. However, during rare and short-lived intervals, the magnetic field became extremely strong — potentially even rivaling Earth’s.
The debate persisted in part because the Apollo missions landed in broadly similar regions, which meant many samples captured the same unusual events.
“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,” said lead author Associate Professor Claire Nichols of the Department of Earth Sciences, University of Oxford. “It now seems that a sampling bias prevented us from realizing how short and rare these strong magnetism events were.”
Analyzing Moon rocks
Mare basalts provided a key clue. The team discovered that the titanium content of these rocks strongly correlated with their magnetic strength. Titanium-rich mare basalts appear to have formed during periods when the Moon’s magnetic field intensified.
The researchers propose that both the volcanic activity and the magnetic surges were triggered by melting of titanium-rich material deep inside the Moon.
“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,” Professor Nichols said. “But that for very short periods of time – no more than 5,000 years, but possibly as short as a few decades – melting of titanium-rich rocks at the Moon’s core-mantle boundary resulted in the generation of a very strong field.”
The Apollo Missions’ Unusual Landing Site
Because these basalt plains were flat and relatively safe, they were selected as Apollo landing locations. As a result, astronauts returned samples disproportionately rich in these unusual rocks, giving scientists a skewed view of the Moon’s magnetic history.
The researchers also developed mathematical models showing that a more representative sampling of lunar terrain would probably not have contained strong magnetic signatures.
“If we were aliens exploring the Earth, and had landed here just six times, we would probably have a similar sampling bias, especially if we were selecting a flat surface to land on,” said Associate Professor Jon Wade of the Department of Earth Sciences, University of Oxford. “It was only by chance that the Apollo missions focused so much on the Mare region of the Moon – if they landed somewhere else, we would likely have concluded that the Moon only ever had a weak magnetic field and missed this important part of early lunar history entirely.”
“We are now able to predict which types of samples will preserve which magnetic field strengths on the Moon,” said Dr. Simon Stephenson of the Department of Earth Sciences, University of Oxford. “The upcoming Artemis missions offer us an opportunity to test this hypothesis and delve further into the history of the lunar magnetic field.”
The recent paper, “An Intermittent Dynamo Linked to High-Titanium Volcanism on the Moon,” appeared in Nature Geoscience on February 25, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.