HISTORY OF THE SOLAR NEBULA FROM METEORITE PALEOMAGNETISM

B P Weiss , R R Fu , H Wang , X.-N Bai , J. Gattacceca (1) , R J Harrison , D L Schrader

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

Introduction: A key stage in the origin of planetary systems is the formation of a gas-rich protoplanetary disk. Theoretical studies suggest that magnetic fields mediated the global evolution and structure of protoplanetary disks by transporting angular momentum and driving disk accretion [1]. However, the nature and history of nebular magnetic fields have been poorly constrained. Here we review recent advances in our understanding of the magnetism of the solar nebula as inferred from meteorites. We discuss their implications for the mechanism and rate of accretion, the dispersal time of the nebula, the formation of chondrules and the gas giants, and planetary migration. The solar nebula and nebular magnetism: Until recently, evidence for magnetic fields in the terrestrial planet-forming regions of disks around young stellar objects (YSOs) and in the early solar system had been absent. Two recent classes of measurements are filling this gap: astronomical and meteoritic studies. Astronomical observations: Although there are presently no techniques available for resolving magnetic fields in the midplane region at stellar distances of ~0.1-50 AU, Zeeman spectroscopy and spectropolarimetry have mapped magnetic field intensities and directions on the surface of T Tauri stars and their innermost disks (<0.05 AU)[2]. The orientations of magnetic fields at scales of >50-100 AU could be mapped via their alignment of the spin axes of aspherical dust grains spun-up by radiation torques, which leads to emission polarized perpendicularly to the field direction [3]. Recent millimeter and mid-infrared observations have observed polarized emission of embedded objects and those with visible disks with masses ranging from ~0.2-2.5 solar masses (M⨀) [3]. However, it is unclear whether the observed polarization is a signature of magnetic fields or is due to dust self-scattering [4, 5]. Meteorite measurements: Recent paleomagnetic measurements of chondrules from the Semarkona meteorite [6] indicate the that solar nebula magnetic field was 5-50 µT in the midplane at ~2-3 AU at the time of chondrule formation at ~1-3 My after the formation of calcium aluminum-rich inclusions (CAIs) (assumed here to be 4567.30 ± 0.16 My ago [7], just after the collapse of the molecular cloud). Furthermore, paleomagnetic studies of seven CM chondrites indicate they were magnetized by a field of >4 ± 3 µT sometime between 2.4-4 My after CAI formation (from I-Xe dating) although it is unclear whether this field was nebular or generated by the CM parent body [8] (note these paleointensities are twice those reported by [8] to take into account rotation of the 2054.

Domaines: Planète et Univers [physics]

B P Weiss, R R Fu, H Wang, X.-N Bai, J. Gattacceca, et al.. HISTORY OF THE SOLAR NEBULA FROM METEORITE PALEOMAGNETISM. Accretion: Building New Worlds, 2017, Houston, United States. ⟨hal-03533006⟩