Time-resolved records of the Earth's planetary magnetic field have been essential in understanding the dynamic history of our planet. Although most rocky planets, moons and asteroids of the solar system do not generate magnetic fields nowadays, they are thought to have generated dynamo fields in the early solar system. The nature and temporal evolution of those fields has remained enigmatic but its understanding could provide a unique insight into planetary evolution.
In the case of asteroids, our foremost source of information regarding magnetic fields comes from meteorites. Regions containing nano-scale islands of tetrataenite (chemically ordered FeNi), found within the meteoritic metallic material, have been recently proposed as reliable remanence carriers. X-ray Photoelectron Emission Microscopy (PEEM) results on meteorites suggest that unconventional mechanisms acted in the early solar system giving rise to a long-lasting and widespread epoch of dynamo activity among small bodies in the early solar system, and might help to explain the long-lived magnetic activity observed in larger bodies, such as the moon.