  In protoplanetary disks, dust grains rich in metallic iron can attract each
other magnetically. If they are magnetized to values near saturation, the
magnetically induced collision speeds are high enough to knock off the
non-magnetized, loosely bound silicates. This process enriches the surviving
portions of the dust grains in metallic iron, which further enhances the
magnetically mediated collisions. The magnetic enhancement to the collisional
cross-section between the iron rich dust results in rapid grain growth leading
to planetesimal formation. While this process of knocking off silicates, which
we term "magnetic erosion", occurs only in a very limited portion of a
protoplanetary disk, it is a possible explanation for Mercury's
disproportionately large iron core.
