Buried Lunar Volcano Provides Evidence of Ancient Magnetic Dynamo

• Researchers from ETH Zurich and other institutions have found evidence that the Moon once possessed a magnetic dynamo by analyzing the 'Dewar Swirl' on the lunar far side.
• The feature is classified as a 'cryptomare'—an ancient basalt deposit buried beneath impact debris—that sits atop a buried volcano.
• The study concludes that the unique reflective brightness of the surface in this area is caused by a horizontal magnetic anomaly protecting the regolith from solar wind weathering.

Scientific Analysis

• The Dewar swirl is located northwest of the South Pole-Aitken (SPA) basin and exhibits both gravitational and magnetic anomalies.
• By using variation of information (VI) techniques on data from missions like GRAIL and Kaguya, researchers identified a massive, dense geological body roughly 60 km wide and 5–9 km deep.
• The magnetic anomaly required hundreds of thousands to millions of years to form, ruling out transient effects like asteroid impacts and confirming an early long-term lunar dynamo.
• Geological dating places the anomaly's formation at approximately 4.22 billion years ago, between the formation of the SPA basin (4.32 Ga) and the Freundlich-Sharonov basin (4.14 Ga).

Implications for Lunar Evolution

• The study estimates the early lunar magnetic field strength was approximately 11 microteslas, compared to Earth's current 50 microteslas.
• Future missions, including the Lunar Vertex lander, Chang’e-7/8, and Artemis surface operations, aim to collect further samples and data to explain how this early dynamo functioned.