Paleomagnetic evidence for a nebular magnetic field from calcium

Paleomagnetic evidence for a nebular magnetic field from calcium-aluminum-rich inclusions Edited by Denton S. Ebel, American Museum of Natural History, New York, NY; received August 7, 2025; accepted June 16, 2026 by Editorial Board Member Peter B. Kelemen Significance A key step in the formation of planetary systems is the collapse of a cloud of gas and dust into a protoplanetary disk. It has been unclear what forces transformed the disk into the final configuration of a central massive star surrounded by planets. In particular, it has been proposed that in the earliest stages of disk evolution gravity and/or magnetism played a central role. Here we report studies of the remanent magnetization in calcium-aluminum-rich inclusions, the oldest known solar system solids. We find that they record ancient magnetic fields with intensities stronger than that of the Earth today. This supports the hypothesis that magnetism played a key role in driving mass transport in the early protoplanetary disk. Abstract 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 103 K at the earliest stages of solar system formation. Data, Materials, and Software Availability All data needed to evaluate the conclusions in the paper is available in the Magnetics Information Consortium (MagIC) Database through the DOI: https://doi.org/10.7288/V4/MAGIC/20586 (87). Acknowledgments We thank K. Righter and the Meteorite Working Group for allocating the samples. We also thank Eduardo A. Lima for helpful discussions. C.S.B. thanks The Morton K. Blaustein Scholars Fund for their support. B.P.W. and E.N.M. thank the NASA Laboratory Analysis of Returned Samples program (80NSSC23K1267) for support. X.-N.B. is supported by NSF of China under grant no. 12325304. R.J.H. thanks the European Union’s Research and Innovation Actions under grant agreements 101005611 and 101131765. P.-Y.T. and R.J.H. acknowledge funding from EXCITE (award no. G106564) and EXCITE2 (award no. G122171). B.P.W. also thanks the NASA Emerging Worlds program (80NSSC25K0347). Author contributions C.S.B. and B.P.W. designed research; C.S.B., P.-Y.T., R.J.H., E.N.M., and N.C. performed research; C.S.B., X.-N.B., P.-Y.T., and E.N.M. contributed new reagents/analytic tools; C.S.B., X.-N.B., P.-Y.T., R.J.H., E.N.M., N.C., F.L.H.T., and K.D.M. analyzed data; and C.S.B., B.P.W., X.-N.B., R.J.H., E.N.M., F.L.H.T., and K.D.M. wrote the paper. Competing interests The authors declare no competing interest. Supporting Information Appendix 01 (PDF) - Download - 28.30 MB References 1 P. J. Armitage, W. Kley, From Protoplanetary Disks to Planet Formation (Springer-Verlag, Berlin Heidelberg, 2019). 2 W. J. Fischer et al., “Accretion variability as a guide to stellar mass assembly” in Protostars and Planets VII, S. Inutsuka, Y. Aikawa, T. Muto, K. Tomida, M. Tamura, Eds. (Astronomical Society of the Pacific, 2023), pp. 355-378. 3 L. Hartmann, N. Calvet, E. Gullbring, P. D’Alessio, Accretion and the evolution of T Tauri disks. Astrophys. J. 495, 385 (1998). 4 D. M. 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This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). Data, Materials, and Software Availability All data needed to evaluate the conclusions in the paper is available in the Magnetics Information Consortium (MagIC) Database through the DOI: https://doi.org/10.7288/V4/MAGIC/20586 (87). Submission history Received: August 7, 2025 Accepted: June 16, 2026 Published online: August 24, 2026 Published in issue: September 8, 2026 Keywords Acknowledgments We thank K. Righter and the Meteorite Working Group for allocating the samples. We also thank Eduardo A. Lima for helpful discussions. C.S.B. thanks The Morton K. Blaustein Scholars Fund for their support. B.P.W. and E.N.M. thank the NASA Laboratory Analysis of Returned Samples program (80NSSC23K1267) for support. X.-N.B. is supported by NSF of China under grant no. 12325304. R.J.H. thanks the European Union’s Research and Innovation Actions under grant agreements 101005611 and 101131765. P.-Y.T. and R.J.H. acknowledge funding from EXCITE (award no. G106564) and EXCITE2 (award no. G122171). B.P.W. also thanks the NASA Emerging Worlds program (80NSSC25K0347). Author contributions C.S.B. and B.P.W. designed research; C.S.B., P.-Y.T., R.J.H., E.N.M., and N.C. performed research; C.S.B., X.-N.B., P.-Y.T., and E.N.M. contributed new reagents/analytic tools; C.S.B., X.-N.B., P.-Y.T., R.J.H., E.N.M., N.C., F.L.H.T., and K.D.M. analyzed data; and C.S.B., B.P.W., X.-N.B., R.J.H., E.N.M., F.L.H.T., and K.D.M. wrote the paper. Competing interests The authors declare no competing interest. Notes This article is a PNAS Direct Submission. D.S.E. is a guest editor invited by the Editorial Board. Authors Metrics & Citations Metrics Altmetrics Citations Cite this article Paleomagnetic evidence for a nebular magnetic field from calcium-aluminum-rich inclusions, Proc. Natl. Acad. Sci. U.S.A. 123 (36) e2521660123, https://doi.org/10.1073/pnas.2521660123 (2026). Copied! Copying failed. Export the article citation data by selecting a format from the list below and clicking Export. View Options View options Download this article as a PDF file. PDFPDF and Supporting Information Download the article PDF and supporting information. Download PDF and supporting informationeReader View this article with eReader. eReaderFigures Tables Media References References References 1 P. J. Armitage, W. Kley, From Protoplanetary Disks to Planet Formation (Springer-Verlag, Berlin Heidelberg, 2019). 2 W. J. Fischer et al., “Accretion variability as a guide to stellar mass assembly” in Protostars and Planets VII, S. Inutsuka, Y. Aikawa, T. Muto, K. Tomida, M. Tamura, Eds. (Astronomical Society of the Pacific, 2023), pp. 355-378. 3 L. Hartmann, N. Calvet, E. Gullbring, P. D’Alessio, Accretion and the evolution of T Tauri disks. Astrophys. J. 495, 385 (1998). 4 D. M. Segura-Cox et al., Four annular structures in a protostellar disk less than 500,000 years old. Nature 586, 228–231 (2020). 5 D. Harsono et al., Evidence for the start of planet formation in a young circumstellar disk. Nat. Astron. 2, 646–651 (2018). 6 G. Lesur et al., “Hydro-, magnetohydro-, and dust-gas dynamics of protoplanetary disks” in Protostars and Planets VII, S. i. Inutsuka, Y. Aikawa, T. Muto, K. Tomida, M. Tamura, Eds. (Astronomical Society of the Pacific, 2023), pp. 465–500. 7 R. D. Blandford, D. G. Payne, Hydromagnetic flows from accretion disks and the production of radio jets. Mon. Not. R. Astr. Soc. 199, 883–903 (1982). 8 X. N. Bai, Wind-driven accretion in protoplanetary disks. II. Radial dependence and global picture. Astrophys. J. 772, 96 (2013). 9 S. A. Balbus, J. F. Hawley, A powerful local shear instability in weakly magnetized disks. I. Linear analysis. Astrophys. J. 376, 214 (1991). 10 S. J. Desch, N. J. Turner, High-temperature ionization in protoplanetary disks. Astrophys. J. 811, 156 (2015). 11 S. Hirose, Magnetic turbulence and thermodynamics in the inner region of protoplanetary discs. Mon. Not. R. Astron. Soc. 448, 3105–3120 (2015). 12 K. Kratter, G. Lodato, Gravitational instabilities in circumstellar disks. Annu. Rev. Astron. Astrophys. 54, 271–311 (2016). 13 K. Tomida, M. N. Machida, T. Hosokawa, Y. Sakurai, C. H. Lin, Grand-design spiral arms in a young forming circumstellar disk. Astrophys. J. Lett. 835, L11 (2017). 14 W. Xu, M. W. Kunz, Formation and evolution of protostellar accretion discs - II. From 3D simulation to a simple semi-analytic model of Class 0/I discs. Mon. Not. R. Astron. Soc. 508, 2142–2168 (2021). 15 B. Huang et al., On the magnetic field properties of protostellar envelopes in Orion. Astrophys. J. Lett. 963, L31 (2024). 16 C. Flores, M. S. Connelley, B. Reipurth, A. Boogert, G. Doppmann, iSHELL K-band survey of Class I and flat spectrum sources: Magnetic field measurements in the protostellar phase. Astrophys. J. 972, 149 (2024). 17 W. Kwon et al., Highly ordered and pinched magnetic fields in the Class 0 protobinary system L1448 IRS 2. Astrophys. J. 879, 25 (2019). 18 J. F. Donati, F. Paletou, J. Bouvier, J. Ferreira, Direct detection of a magnetic field in the innermost regions of an accretion disk. Nature 438, 466–469 (2005). 19 R. Teague et al., A radially resolved magnetic field threading the disk of TW Hya. Astrophys. J. Lett. 991, L6 (2025). 20 B. P. Weiss, X. N. Bai, R. R. Fu, History of the solar nebula from meteorite paleomagnetism. Sci. Adv. 7, eaba5967 (2021). 21 C. S. Borlina, B. P. Weiss, J. F. J. Bryson, P. J. Armitage, Lifetime of the outer solar system nebula from carbonaceous chondrites. J. Geophys. Res. 127, e2021JE007139 (2022). 22 J. F. J. Bryson, C. I. O. Nichols, C. 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