The end of the lunar dynamoOPEN ACCESS 

Saied Mighani, Huapei Wang, David L. Shuster, Cauȇ S. Borlina, Claire I. O. Nichols, Benjamin P. Weiss

Science Advances 01 Jan 2020:
Vol. 6, no. 1, eaax0883
DOI: 10.1126/sciadv.aax0883


“Magnetic measurements of the lunar crust and Apollo samples indicate that the Moon generated a dynamo magnetic field lasting from at least 4.2 until <2.5 billion years (Ga) ago. However, it has been unclear when the dynamo ceased. Here, we report paleomagnetic and 40Ar/39Ar studies showing that two lunar breccias cooled in a near-zero magnetic field (<0.1 μT) at 0.44 ± 0.01 and 0.91 ± 0.11 Ga ago, respectively. Combined with previous paleointensity estimates, this indicates that the lunar dynamo likely ceased sometime between ~1.92 and ~0.80 Ga ago. The protracted lifetime of the lunar magnetic field indicates that the late dynamo was likely powered by crystallization of the lunar core.”