PALEOMAGNETISM OF CALCIUM-ALUMINUM-RICH INCLUSIONS

Magnetic fields have been proposed to play a central role in the evolution of protoplanetary disks by transporting mass and angular momentum. Paleomagnetic studies of meteorites have shown that magnetic fields of ~50-100 µT existed within ~7 AU of the Sun at ~2-3 million years (Ma) after the formation of calcium-aluminum-rich inclusions (CAIs), dispersing by ~4 Ma after CAI formation. Nonetheless, the existence of magnetic fields and their role prior to 2 Ma after CAI formation remains undetermined. Here, we seek to establish the magnetic field of the solar nebula during its first ~20-50 thousand years by obtaining paleomagnetic measurements of CAIs. This might also shed light on CAI’s poorly-understood formation and transport mechanisms. If CAIs acquired their magnetic records close to the Sun (<0.1 AU), they would have experienced fields >10⁴ µT, while if they acquired in the outer solar system (>3 AU) these would have been ~100 µT. To address this, we analyzed mutually-oriented CAIs extracted from the CO3.00 chondrite DOM 08006 for which our previous studies of bulk samples and chondrules indicate has not been remagnetized since its accretion. Alternating field demagnetization of six CAIs reveals three CAIs with stable magnetization components with coercivities up to 145 mT. Paleointensities obtained from these CAIs indicate that they formed in ancient fields of 147.7 ± 22.7 µT. Backscattered electron microscopy images indicate that the magnetic carriers are likely to be small (<0.5 µm) nearly pure Fe kamacite. This indicates the presence of magnetic fields during the very beginning of the solar system and is likely the oldest known paleomagnetic record yet identified from any sample. When coupled to models that describe magnetically-driven accretion in protoplanetary disks, our results suggest that CAIs likely acquired their magnetic record at >8 AU. Given that previous isotopic, mineralogical and redox studies favor a formation of CAIs <0.1 AU from the Sun, our records suggest that CAIs acquired magnetization through reheating during or after transport to the outer solar system, potentially associated with magnetized disk winds and stellar outbursts. Ongoing studies will investigate the CAI’s isotopic composition and rock magnetic properties to determine the nature and origin of their magnetization.