Advances in Planetary Magnetism from Quantum Diamond Microscopy

Presented by Sarah Steele (Harvard University). Understanding the magnetic histories of terrestrial bodies such as the Moon, Mars, and Mercury can provide unique insights into their thermal histories and deep interior properties. However, there are distinct challenges associated with interpreting both remotely sensed magnetic observations and the paleomagnetic records preserved in individual meteorites. Deriving magnetic histories from crustal magnetic surveys is complicated by poorly known magnetic mineralogies, high measurement altitudes, and uncertain magnetic source regions. Meteorite- and returned-sample-based studies must contend with limited sample volumes, complex shock and heating histories, and alteration-prone magnetic mineralogies. New techniques for micron-scale magnetic imaging with the Quantum Diamond Microscope (QDM) can address some of these obstacles by enabling the study of samples with complex magnetic histories, maximizing return from small sample volumes, and permitting detailed in situ magnetic characterization. We discuss two distinct applications of quantum diamond microscopy to problems in planetary magnetism. First, we present results from a QDM-based paleomagnetic study of the martian meteorite ALH 84001. Although ALH 84001 contains multiple magnetic populations of different ages, partly due to submillimeter variations in temperature and pressure experienced during several shock events in its history, QDM-based techniques enabled us to characterize magnetization in several of these populations. Second, we discuss the recent use of quantum diamond microscopy to characterize magnetic mineralogies of highly reduced samples, with important implications for interpreting crustal magnetization on reduced bodies such as Mercury and the Moon. By pairing micron-scale magnetic imagery of aubrites and eucrites with compositional measurements from electron microscopy, we identify remanence-hosting phases in situ. We observe remanence associated with pyrrhotite in several reduced samples, suggesting that Fe-depleted pyrrhotite may be stable under more reducing conditions than previously expected. These studies demonstrate the QDM’s utility for interpreting remanence in samples with complex magnetic histories and for characterizing exotic magnetic mineralogies.