Ferromagnetism and particle collisions: applications to protoplanetary disks and the meteoritical record

TL;DR

This paper explores how magnetic interactions between iron-rich dust grains in protoplanetary disks can increase collision rates, potentially explaining isotopic partitioning observed in meteorites and influencing early planetary formation.

Contribution

It provides a parameterization for magnetic dipole interactions affecting particle collisions and assesses their significance in protoplanetary disk environments.

Findings

Magnetic fields in disks can magnetize iron-bearing dust grains.

Magnetic interactions can significantly increase collision rates.

This mechanism may preserve isotopic inhomogeneities in meteorites.

Abstract

The meteoritical record shows both iron partitioning and tungsten isotopic partitioning between matrix and chondrules. Tungsten is not abundant enough to have driven its own isotopic partitioning, but if tungsten were correlated with iron, then ferromagnetic interactions grains could help explain both observations. We derive a practical parameterization for the increase in particle-particle collision rates caused by mutually attracting particle magnetic dipole moments. While the appropriate magnetic parameters remain uncertain, we show that ambient magnetic fields in protoplanetary disks are expected to be strong enough to magnetize iron metal bearing dust grains sufficiently to drive large increases in their collision rates. Such increased collision rates between iron metal rich grains could help preserve primordial iron and W isotopic inhomogeneities; and would help explain why the meteoritical record shows their partitioning in the solar nebula. The importance of magnetic interactions for larger grains whose growth is balanced by fragmentation is less clear, and will require future laboratory or numerical studies.