# Seeding the Formation of Mercurys: An Iron-sensitive Bouncing Barrier in Disk Magnetic Fields

## TL;DR

This study investigates how magnetic fields influence dust aggregation in protoplanetary disks, revealing that magnetic forces promote iron-rich cluster formation, potentially explaining planetary composition gradients.

## Contribution

It demonstrates that magnetic fields induce clustering of iron-rich dust, leading to larger aggregates and suggesting a mechanism for iron enrichment in inner planetary regions.

## Key findings

- Magnetic fields cause reversible clustering of dust particles.
- Iron-rich dust forms larger clusters than quartz in magnetic fields.
- Cluster size increases with magnetic field strength and iron content.

## Abstract

The inner part of protoplanetary disks can be threaded by strong magnetic fields. In laboratory levitation experiments, we study how magnetic fields up to 7 mT influence the aggregation of dust by observing the self-consistent collisional evolution of particle ensembles. As dust samples we use mixtures of iron and quartz in different ratios. Without magnetic fields, particles in all samples grow into a bouncing barrier. These aggregates reversibly form larger clusters in the presence of magnetic fields. The size of these clusters depends on the strength of the magnetic field and the ratio between iron and quartz. The clustering increases the size of the largest entities by a factor of a few. If planetesimal formation is sensitive to the size of the largest aggregates, e.g., relying on streaming instabilities, then planetesimals will preferentially grow iron-rich in the inner region of protoplanetary disks. This might explain the iron gradient in the solar system and the formation of dense Mercury-like planets.