Measuring the intensity of the Moon's ancient magnetic field is an important goal of lunar sample analysis. Paleointensity estimates using thermal methods (Thellier–Thellier) raise the problem of sample alteration, especially for lunar samples carrying sulfides. To address this problem, we made real-time measurements of sample magnetization during heating with a three-axis vibrating sample magnetometer (the Triaxe, LeGoff and Gallet, 2004), in the hope that rapid heating would minimize alteration (Coe et al., 2014). We studied the Millbillillie meteorite, which has a lunar-like mineralogy. We find that after repeated heating phases to ∼600 °C, we form pyrrhotite, magnetite, and magnetic phases with low (200–270 °C) Curie temperatures. These low-temperature phases appear after pyrrhotite has apparently been destroyed by subsequent heating phases, and their mineralogy is unknown. These results have implications for the paleomagnetic study of any extraterrestrial samples with even small amounts of sulfides, and further experiments are required to understand them.
Bibliographical noteFunding Information:
Cécile Cournède, Ian Garrick-Bethell, and Robert Coe acknowledge support from the NASA Solar System Workings Program (grant # NNX15AH47G). This work was partially supported by the BK21 plus program through the National Research Foundation (NRF), funded by the Ministry of Education of Korea and the Louis Gentil–Jacques Bourcart award from the French “Académie des sciences”. The first author was invited by the chief editor to propose a paper, as the recipient of one of the Academy of Sciences prizes for 2015. The authors also thank Pierre Rochette for his helpful comments. The chief editor thanks Pierre Rochette for his review of this invited paper.
- Apollo samples
- Millbillillie meteorite
- Mineralogical changes
- Paleointensity recovery
- Thermal method