A new study of ancient iron meteorites suggests that the very first solid bodies in the Solar System were assembled from tiny, heat-forged rock beads called chondrules. These meteorites, which are fragments of planetesimals that formed early on, show that water-rich dust played only a minor role in their construction. The finding points to a process that actively selected for heat-processed material while leaving icy components behind.
The analysis pushes this selective planet-building mechanism back to the Solar System's first million years, earlier than previously established. Rather than a uniform mix of dusty and icy grains, the earliest planetesimals appear to have been built from a narrow range of ingredients. This suggests that high-temperature events, such as shocks or radiation from the young Sun, may have dominated the environment where these bodies took shape.
The results add a new layer to our understanding of planetary formation. They imply that the conditions in the nascent Solar System were not merely chaotic, but chemically and thermally sorted from the very beginning. While the study is based on a single set of meteorite samples, its implications align with models that favor rapid, hot accretion over cold, ice-rich assembly for the first generation of solid bodies.