Iron meteorites are remnants of the metallic cores of the earliest asteroids in our solar system. Iron meteorites contain refractory metals, such as iridium and platinum, that formed near the sun but were transported to the outer solar system. New research shows that for this to have happened, the protoplanetary disk of our solar system had to have been doughnut-shaped because the refractory metals could not have crossed the large gaps in a target-shaped disk of concentric rings. The paper suggests that the refractory metals moved outward as the protoplanetary disk rapidly expanded, and were trapped in the outer solar system by Jupiter.