Early Outer Solar System Planetesimals Were 92% Heat-Forged Rock, Not Ice-Rich Dust
New research published in Nature Astronomy suggests that the first planetesimals in the outer Solar System were composed of up to 92% heat-processed chondrules, with only 8-17% fine, volatile-rich matrix. This indicates that gas dynamics in the young solar nebula selectively filtered out icy dust, allowing larger, denser rocky particles to accrete first. The findings, based on chemical reconstructions of carbonaceous iron meteorites, push evidence for selective planet building back to the Solar System's first million years, challenging the assumption that early outer worlds simply accumulated all available local material.