ETH Zurich study finds hidden volcanic complex behind Moon's ancient magnetic field

September 26, 2026 at 05:18 PM1 min

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Researchers from ETH Zurich have identified a massive subsurface rock body in the Moon's Dewar region that may explain the Moon's ancient magnetic field. The study, published in Science Advances, combines gravity and magnetic data from multiple lunar missions to reveal a 60-kilometer-wide volcanic complex extending to a depth of nine kilometers. The findings challenge the long-standing dynamo theory, suggesting instead that the magnetic anomaly is linked to localized volcanic activity.

Key Facts

The Dewar region on the Moon's far side shows a magnetic anomaly coinciding with a gravity anomaly, indicating denser and more strongly magnetized rock.
The subsurface rock body is 60 kilometers wide and extends to a depth of nine kilometers.
The study was published in Science Advances by researchers including Xi Yang and Anna Mittelholz from ETH Zurich.
The analysis used gravity data from NASA's GRAIL mission and magnetic field models from Lunar Prospector and Kaguya.

The Dewar Anomaly

In the Dewar region, a pronounced magnetic field anomaly and a distinct gravity anomaly coincide spatially. The rock there is measurably denser and far more strongly magnetized than the surrounding lunar crust. A specialized inversion algorithm processed the combined gravity and magnetic data to produce a detailed three-dimensional subsurface model. The model reveals a massive rock body 60 kilometers wide reaching nine kilometers deep.

Competing Theories

Apollo mission rock samples yielded contradictory evidence about the Moon's magnetic past, with some analyses indicating a strong field 4.25 to 3.5 billion years ago and others finding none. The dynamo theory proposes an internal magnetic field generated by the movement of liquid iron, similar to Earth's core. The impact theory suggests that massive asteroid strikes caused only superficial, time-limited magnetization. The new study's findings support a volcanic origin for the magnetic anomaly, challenging the dynamo explanation.