The moon’s magnetic field has long puzzled scientists, and a fresh analysis of lunar rocks collected during NASA’s Apollo missions is now reshaping how researchers describe it. In a study published in Nature Geoscience, Claire Nichols of the University of Oxford and her team reported that the moon’s magnetic field remained weak for most of its existence but strengthened during brief intervals in deep geologic time.
Nichols and her colleagues said those intervals occurred between about 3 billion and 4 billion years ago, when the moon’s magnetic activity strengthened and even exceeded Earth’s magnetic activity, according to the findings reported Wednesday. The team described the spikes as short-lived, with the strongest field periods far briefer than earlier interpretations suggested.
Nichols said the moon produced “incredibly short spikes in high magnetic field strength” that lasted no more than 5,000 years and possibly as short as a few decades. The researchers tied the spikes to internal processes, saying the short bursts likely resulted from the melting of titanium-rich rocks deep within the moon.
In their analysis, the Oxford researchers said they revisited earlier measurements from Apollo samples and connected high titanium levels with preserved traces of high magnetic activity. They said rocks from Apollo’s first and last moon landings—Apollo 11 and Apollo 17—contained high titanium, helping provide the geochemical link used to infer past magnetic conditions.
The study also argued that magnetic-field evidence from Apollo samples was not representative of conditions across the moon more broadly. It said the Apollo rocks came from similar locales where titanium was abundant, brought to the surface through volcanic eruptions, rather than from regions that might better capture the moon’s ancient magnetic history.
The researchers said future data from NASA’s Artemis program could address that limitation by targeting different regions of the moon. With Artemis astronauts expected to fly around the moon in a test flight as early as April from Kennedy Space Center after weeks of delays, the mission is expected to collect new samples that, the study suggested, could clarify how the moon’s ancient magnetism evolved. The paper said Artemis astronauts will explore the lunar south polar region rather than the low-latitude lava plains that characterized Apollo-era sampling.
Nichols said understanding the history of the moon’s magnetic shield is important for what scientists may infer about the moon’s capacity to support habitable conditions. She said the shield’s evolution is “critical for thinking about planetary habitability,” in comments reported alongside the study.