Long-lived magnetism from solidification-driven convection on the pallasite parent body

James F. J. Bryson, Claire I. O. Nichols,Julia Herrero-Albillos, Florian Kronast,Takeshi Kasama, Hossein Alimadadi, Gerrit van der Laan, Francis Nimmo, Richard J. Harrison

Nature 517, 472–475, (22 January 2015), doi:10.1038/nature14114

LINK (abstract)

A rock hard drive
Meteorites found on earth contain a well preserved record of their magnetic history and could teach us about the early solar system. Reporter Lizzie Gibney speaks to researcher James Bryson about using meteorites to study the history of the solar system.

Palaeomagnetic measurements of meteorites1, 2, 3, 4, 5 suggest that, shortly after the birth of the Solar System, the molten metallic cores of many small planetary bodies convected vigorously and were capable of generating magnetic fields6. Convection on these bodies is currently thought to have been thermally driven7, 8, implying that magnetic activity would have been short-lived9. Here we report a time-series palaeomagnetic record derived from nanomagnetic imaging10 of the Imilac and Esquel pallasite meteorites, a group of meteorites consisting of centimetre-sized metallic and silicate phases. We find a history of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shutdown of the magnetic field as core solidification completed. We demonstrate that magnetic activity driven by progressive solidification of an inner core11, 12, 13 is consistent with our measured magnetic field characteristics and cooling rates14. Solidification-driven convection was probably common among small body cores15, and, in contrast to thermally driven convection, will have led to a relatively late (hundreds of millions of years after accretion), long-lasting, intense and widespread epoch of magnetic activity among these bodies in the early Solar System.