Solar Nebula Accretion Studied with Paleomagnetism - Caue Borlina - 2021 MagIC Workshop (1/20/21)
Channel: Magnetics Information Consortium (MagIC)
Date: 2021-01-25

"Non-steady Accretion in the Solar Nebula Inferred from Paleomagnetism of CO Chondrules" by Caue Borlina, Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology.

Lightning poster talk presented at the virtual 2021 MagIC Workshop (https://earthref.org/events/MAGIC/2021/) - Rock and Paleomagnetism through Time and Space. Jan 19th-21st, 2021.


Abstract:
"Non-steady Accretion in the Solar Nebula Inferred from Paleomagnetism of CO Chondrules"
C. S. Borlina(1), B. P. Weiss(1), J. F. J. Bryson(2), E. A. Lima(1), Xue-Ning Bai(3)
(1)Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA, (2)Department of Earth Sciences, University of Oxford, Oxford, UK, (3)Institute for Advanced Study, Tsinghua University, Beijing, China


Magnetic fields have been hypothesized to play a central role during the evolution of the protoplanetary disk [1]. In support of this, previous paleomagnetic measurements support the presence of magnetic fields during the first few million years after the formation of the calcium-aluminum-rich inclusions (CAIs) [2, 3]. Isotopic measurements indicate that known meteorites are derived from two main regions: the non-carbonaceous and carbonaceous reservoirs [4]. Here we assess the nature and origin of the gap that separated these reservoirs using paleomagnetic measurements. While the LL chondrule records of the nebular magnetic field were obtained for the non-carbonaceous reservoir robust chondrule records of the carbonaceous region have been lacking.
To address this, we targeted chondrules from the pristine CO carbonaceous chondrites DOM 08006 (type 3.00) and ALHA 77307 (type 3.03) to obtain records of the magnetic field at ~2.5 Ma after CAI formation in the carbonaceous reservoir [5, 6]. We targeted dusty olivine chondrules from these samples since they are known to be robust paleomagnetic recorders containing metal grains that formed prior to accretion of the CO parent body [3, 7-9]. The chondrules were demagnetized using stepwise alternating fields and their natural remanent magnetization measured using superconducting quantum interference device (SQUID) microscopy at MIT [10]. Paleointensity estimates were acquired using anhysteretic remanent magnetization methods which have been previously calibrated for dusty olivine thermoremanent magnetization [7].


Our results support the presence of magnetic fields in the carbonaceous reservoir at ~2.5 Ma after CAI formation with a mean paleointensity of 96.2 ± 10.1 μT (2s). When compared to previous measurements and models that describe the expected spatial distribution of the magnetic field in protoplanetary disk, we observe that our measurements do not follow the expected decay of the magnetic strength for a disk with a smoothly decaying mass distribution and constant accretion rate [3, 11]. These results support the presence of non-steady state accretion in the early solar system, resulted from a tenfold increase in the accretion rate over time and/or from spatial inhomogeneities in the magnetic field intensity. While an increase in the accretion rate could have been associated with accretion bursts [12], the presence of inhomogeneities could have been associated with the existence of density substructures in the disk [13-16]. Finally, our measurements support an additional hypothesis for disk substructure formation, where magnetic inhomogeneities could have created the gap that separated the non- carbonaceous and carbonaceous reservoirs [13].


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