A lunar core dynamo limited to the Moon's first ~140 million years

Area of Science:

• Lunar geology
• Paleomagnetism
• Planetary science

Background:

• The existence and duration of the Moon's core dynamo are debated.
• Some Apollo basalt samples suggest an episodic lunar dynamo, but this is energetically and temporally problematic.

Purpose of the Study:

• To investigate the enigma of the lunar dynamo using paleomagnetic analysis of Apollo samples.
• To constrain the timing and nature of any early lunar magnetic field.

Main Methods:

• Single crystal paleointensity (SCP) analysis of Apollo basalts (70035, 75035) and breccia (61016).
• Comparison of SCP results with whole rock magnetization analyses.
• Dating of lunar samples to establish temporal constraints.

Main Results:

• Whole rock analyses of ~3.7 billion-year-old Apollo basalts yielded high magnetizations, but SCP indicated null fields, refuting an episodic dynamo in these samples.
• SCP studies of older Apollo samples (breccia 61016, ferroan anorthosite 60025) also yielded null values.
• These findings constrain a potential lunar core dynamo to the Moon's first 140 million years.

Conclusions:

• The Moon likely lacked a long-lived core dynamo.
• Early lunar magnetic field, if present, was short-lived, possibly confined to the first 140 million years.
• The Moon's lack of a magnetosphere may have allowed trapping of Earth's Hadean atmosphere in lunar regolith, a target for future exploration.