Paleomagnetic evidence for a nebular magnetic field from calcium-aluminum-rich inclusions

The initial stage of planet formation is expected to take place in a nascent protoplanetary disk (PPD) accreting onto the protostar embedded in an infalling envelope. This stage is likely accompanied by the formation of high-condensation temperature solids resembling calcium-aluminum-rich inclusions (CAIs), the oldest known solar system solids. However, it is unknown whether magnetism and/or gravity dominantly drove accretion in the youngest evolutionary stages of PPDs and the solar nebula. Here we report paleomagnetic measurements of CAIs indicating that they record a nebular magnetic field of ∼150 to 600 μT. This intensity is consistent with magnetic fields playing a key role driving disk accretion while also heating the very inner disk to 10 3 K at the earliest stages of solar system formation.