Weak Magnetic Fields in the Outer Solar Nebula Recorded in CR Chondrites

Roger R. Fu, Pauli Kehayias, Benjamin P. Weiss, Devin L. Schrader, Xue‐Ning Bai, Jacob B. Simon

JGR Planets
Volume 125, 5 May 2020


” – Paleomagnetic measurements of carbonaceous chondrites can provide important constraints on outer solar system magnetic fields
– Our measurements on primitive CR chondrules show that they formed in a magnetic field ≤8 μT
– Such low fields suggest either spatial variations in the nebular magnetic field or incipient dissipation of the nebula by 3.7 Myr after CAIs”

“Theoretical investigations suggest that magnetic fields may have played an important role in driving rapid stellar accretion rates and efficient planet formation in protoplanetary disks. Experimental constraints on magnetic field strengths throughout the solar nebula can test the occurrence of magnetically driven disk accretion and the effect of magnetic fields on planetary accretion. Here we conduct paleomagnetic experiments on chondrule samples from primitive CR (Renazzo type) chondrites GRA 95229 and LAP 02342, which likely originated in the outer solar system between 3 and 7 AU approximately 3.7 million years after calcium aluminum‐rich inclusion formation. By extracting and analyzing 18 chondrule subsamples that contain primary, igneous ferromagnetic minerals, we show that CR chondrules carry internally non‐unidirectional magnetization that requires formation in a nebular magnetic field of ≤8.0 ± 4.3 μT (2σ). These weak magnetic fields may be due to the secular decay of nebular magnetic fields by 3.7 million years after calcium aluminum‐rich inclusions, spatial heterogeneities in the nebular magnetic field, or a combination of both effects. The possible inferred existence of spatial variations in the nebular magnetic field would be consistent with a prominent role for disk magnetism in the formation of density structures leading to gaps and planet formation.”