Magnetization of carbonaceous asteroids by nebular fields and the origin of CM chondrites

Abstract

The solar nebula carried a strong magnetic field that had a stable intensity and direction for periods of a thousand years or more 1 . The solar nebular field may have produced post-accretional magnetization in at least two groups of meteorites, CM and CV chondrites 1-3 , which originated from planetesimals that may have underwent aqueous alteration before gas in the solar nebula dissipated 1,3 . Magnetic minerals produced during aqueous alteration, such as magnetite and pyrrhotite 4 , could acquire a chemical remanent magnetization from that nebular field 3 . However, many questions about the size, composition, formation time, and, ultimately, identity of the parent bodies that produced magnetized CM and CV chondrites await answers-including whether a parent body might exhibit a detectable magnetic field today. Here, we use thermal evolution models to show that planetesimals that formed between a few Myr after CAIs and ~1 Myr before the nebular gas dissipated could acquire from the nebular field, and retain until today, a chemical remanent magnetization throughout nearly their entire volume. Hence, in-situ magnetometer measurements of C-type asteroids could help link magnetized asteroids to magnetized meteorites. Specifically, a future mission could search for a magnetic field as part of testing the hypothesis that 2 Pallas is the parent body of the CM chondrites 5 . Overall, large carbonaceous asteroids might record ancient magnetic fields in magnetic remanence that produces strong modern magnetic fields, even without a metallic core that once hosted a dynamo.