The early phase lunar magnetic field as recorded by Apollo 17 mare basalts
Abstract
Lunar rocks provide evidence that the Moon once sustained a lunar core dynamo. Several studies have provided evidence that the lunar magnetic field during the period 4.25 to 3.56 Ga had a strength similar to that of the Earth nowadays. However, dynamo scaling laws suggest that the Moon lacks the energy budget required to sustain a convective dynamo that could generate such a strong magnetic field continuously throughout this period. This possible discrepancy has motivated the hypothesis that the lunar dynamo field was only intermittently strong during this time. To test this hypothesis, we have been conducting paleomagnetic, rock magnetic, and petrologic measurements on four 3.7 billion years old Apollo 17 mare basalts with textures ranging from coarse- to fine-grained. Using alternating field demagnetization and remagnetization experiments, we show that the recording properties of these samples exhibit a large variability, even on the millimeter-scale. In particular, we find that using the anhysteretic remanent magnetization paleointensity method, we can accurately retrieve paleointensities from thermoremanence acquired in minimum fields ranging from 7 to 75 T over the coercivity range 3-70 mT. According to our results thus far, all 10 subsamples that can record fields at least as low as 20 T have recorded magnetizations which correspond to paleointensities of several tens of T. Therefore, we have yet to confidently identify samples dating from the early phase of the lunar dynamo that recorded a low lunar paleofield.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMGP44A..05V