Detrital remanent magnetization in the solar nebula

Abstract

We introduce the theoretical basis of a new form of remanent magnetization that likely formed on primitive bodies in the solar system. Accretional detrital remanent magnetization (ADRM) operates via “compass needle”-type alignment of ferromagnetic solids with locally uniform background fields in the solar nebula. Accretion of coherently aligned magnetic particles should have formed aggregates up to centimeters in size with significant net magnetic moment. We quantify several processes that constrain the likelihood of ADRM formation, finding that rotational gas damping and background field intensities expected for the solar nebula are sufficient to mutually align magnetic particles with diameters between ∼30 μm and several cm. The lower bound is dictated by Brownian motion or radiative torque while the upper bound is set by aerodynamic torque on non-spherical particles. Processes important for interstellar dust dynamics such as Larmor-type precession and Purcell torque are less significant in the solar nebula. ADRM can be potentially observed as zones of coherent magnetization in primitive chondrites and may be detected by spacecraft magnetic field observations on the surfaces of small bodies. Observational identification and characterization of ADRM would constrain the strength and geometry of magnetic fields in the early solar system, the accretion process of sub-meter sized objects, the formation regions of chondrite parent bodies, and the alteration history of chondritic components.