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

1Roger R. Fu,1,2Pauli Kehayias,1Benjamin P. Weiss,3Devin L. Schrader,4Xue‐Ning Bai,5,6,7Jacob B. Simon
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006260]
1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
2Sandia National Laboratories, Albuquerque, NM, USA
3Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
4Institute for Advanced Study, Tsinghua University, Beijing, China
5Department of Physics and Astronomy, Iowa State University of Science and Technology, Ames, IA, USA
6JILA, University of Colorado Boulder and NIST, Boulder, CO, USA
7Department of Space Studies, Southwest Research Institute, Boulder, CO, USA
Published by arrangement with John Wiley & Sons

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.

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