A two-billion-year history for the lunar dynamo

作者：Tikoo Sonia M^*; Weiss Benjamin P; Shuster David L; Suavet Clement; Wang Huapei; Grove Timothy L

来源：Science Advances, 2017, 3(8): e1700207.

DOI：10.1126/sciadv.1700207

Magnetic studies of lunar rocks indicate that theMoon generated a core dynamo with surface field intensities of similar to 20 to 110 mu T between at least 4.25 and 3.56 billion years ago (Ga). The field subsequently declined to <similar to 4 mu Tby 3.19Ga, but it has been unclearwhether the dynamo had terminated by this time or just greatly weakened in intensity. We present analyses that demonstrate that the melt glass matrix of a young regolith breccia was magnetized in a similar to 5 +/- 2 mu T dynamo field at similar to 1 to similar to 2.5 Ga. These data extend the known lifetime of the lunar dynamo by at least 1 billion years. Such a protracted history requires an extraordinarily long-lived power source like core crystallization or precession. No single dynamo mechanism proposed thus far can explain the strong fields inferred for the period before 3.56 Ga while also allowing the dynamo to persist in such a weakened state beyond similar to 2.5 Ga. Therefore, our results suggest that the dynamo was powered by at least two distinct mechanisms operating during early and late lunar history.

• 出版日期2017-8