Abstract

Planetary magnetic fields are generated by vigorous convection of an electrically-conductive, molten metallic core. Paleomagnetic measurements have revealed that a surprising number of small planetesimals, with radii of just a few hundred kilometres, were able to sustain active magnetic fields in their early histories. This provides invaluable insight into their interior structure, formation and thermal histories. In order to extract these magnetic field histories, many novel experimental approaches have been utilized including synchrotron X-ray microscopy and quantum diamond microscopy. In particular, these methods have allowed paleomagnetic records to be extracted from tetrataenite, a mineral with an exceptionally robust ability to preserve records of magnetic fields that were active billions of years ago. Paleomagnetic records extracted from nanoscale tetrataenite structures in pallasite meteorites have demonstrated that the parent body must have had a large core and a thin mantle. Also, contrary to popular belief, these results show that pallasites do not represent core-mantle-boundary material. The formation of pallasite meteorites remains debated with several formation mechanisms currently in contention including ferrovolcanism, impacts and partial differentiation. By combining paleomagnetic data with petrological and geochemical observations, each of the proposed mechanisms can be systematically ruled in or out. Determining the nature and formation of small planetary bodies is key in understanding the processes that eventually resulted in the formation of the planets in our solar system today.