title: Long-lived magnetism from solidification-driven convection on the pallasite parent body.
abstract: Palaeomagnetic measurements of meteorites 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 fields. Convection on these bodies is currently thought to have been thermally driven, implying that magnetic activity would have been short-lived. Here we report a time-series palaeomagnetic record derived from nanomagnetic imaging 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 core is consistent with our measured magnetic field characteristics and cooling rates. Solidification-driven convection was probably common among small body cores, 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.
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
authors.forename: James F J
authors.initials: JF
authors.lastname: Bryson
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
authors.forename: Claire I O
authors.initials: CI
authors.lastname: Nichols
authors.affiliation: 1] Centro Universitario de la Defensa, Carretera de Huesca s/n, E-50090 Zaragoza, Spain [2] Instituto de Ciencia de Materiales de Aragón, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza, Spain.
authors.forename: Julia
authors.initials: J
authors.lastname: Herrero-Albillos
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Kronast
authors.affiliation: Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kasama
authors.affiliation: Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark.
authors.forename: Hossein
authors.initials: H
authors.lastname: Alimadadi
authors.affiliation: Diamond Light Source, Chilton, Didcot, Oxfordshire OX11 0DE, UK.
authors.forename: Gerrit
authors.initials: G
authors.lastname: van der Laan
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Santa Cruz, California 95064, USA.
authors.forename: Francis
authors.initials: F
authors.lastname: Nimmo
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Harrison