Magnetized magma intrusions identified as sources of lunar magnetic anomalies

Magnetized magma intrusions identified as sources of lunar magnetic anomalies
by Simon Mansfield
Sydney, Australia (SPX) Oct 03, 2024

A team of researchers led by Professor Shuo Yao from China University of Geosciences (Beijing) and her doctoral student Hongyi Wang has revealed that magnetized magma intrusions are the source of two lunar magnetic anomalies. Using a 3D amplitude inversion technique originally developed at the University of British Columbia's Geophysical Inversion Facility (UBC-GIF), the team has made significant progress in understanding the origins of lunar magnetic carriers.

The team carefully validated the amplitude inversion technique to ensure it was suitable for lunar studies, where the magnetic anomaly's direction is complex, the Curie depth is unknown, and the surface grid spacing differs significantly from that of Earth. By assuming a spherical magnetized body and applying a depth weighting function, they successfully reconstructed the 3D distribution of magnetization. This reconstruction provided key insights into the depth and thickness of the magnetic carriers in the lunar crust, helping to determine their origin.

Their study focused on two distinct lunar magnetic anomalies: a weak anomaly in Mare Tranquillitatis and a strong one known as Reiner Gamma in Oceanus Procellarum. Data from the Lunar Prospector and Kaguya spacecraft were used to model the surface magnetic anomalies in these regions, with surface ages estimated at 3.6 and 3.3 billion years, respectively - timeframes just before the intensity drop of the Moon's ancient magnetic field.

According to their findings, the depth to the bottom of the magnetic carriers is approximately 50 km under Mare Tranquillitatis and about 30 km beneath Reiner Gamma. The study revealed that these anomalies are due to magnetized magma intrusions rather than impact melt layers. Notably, the maximum magnetization under Reiner Gamma was found to be about 3.0 A/m. Given the possibility that the magnetized materials under Reiner Gamma predate the surface materials, the intensity of the ancient lunar magnetic field was deduced to have been around several microteslas 3.3 billion years ago.

The research sheds new light on the magnetic history of the Moon, providing crucial evidence that magnetized magma intrusions played a significant role in forming the Moon's magnetic anomalies.

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