A two-billion-year history for the lunar dynamo

Area of Science:

• Lunar geology and geophysics
• Paleomagnetism
• Planetary science

Background:

• The Moon possessed a core dynamo generating significant surface magnetic fields (20-110 μT) from at least 4.25 to 3.56 billion years ago (Ga).
• The lunar dynamo's field intensity decreased to <~4 μT by 3.19 Ga, leaving its termination or weakening uncertain.

Purpose of the Study:

• To determine the duration and intensity of the lunar dynamo's activity in its later stages.
• To investigate the power sources capable of sustaining the lunar dynamo over extended periods.

Main Methods:

• Analysis of magnetic properties in the melt glass matrix of a young lunar regolith breccia.
• Paleointensity determination of the ancient lunar dynamo field.

Main Results:

• The study demonstrates magnetization in a ~5 ± 2 μT dynamo field between approximately 1 and 2.5 Ga.
• These findings extend the known active lifetime of the lunar dynamo by at least 1 billion years.
• The inferred field intensities suggest the dynamo persisted in a weakened state beyond 3.19 Ga.

Conclusions:

• The lunar dynamo's extended history (over 1 billion years) necessitates long-lived power sources, such as core crystallization or precession.
• The distinct field intensities before 3.56 Ga and after 2.5 Ga suggest the dynamo was powered by at least two different mechanisms throughout lunar history.