From the start, the solar system chose fire over ice to build its first bodies

The study reveals that the early solar system favored the formation of chondrules over matrix, which are millimeter-sized rock fragments and cold, icy dust, respectively. Researchers from Yale found that the first million years after the solar system formed, the earliest bodies in the outer solar system were mostly made of chondrules, with very little of the icy, volatile-rich dust that later forms planets. The findings suggest that the process of forming solid bodies was highly selective, favoring heat-forged chondrules over matrix.

The study used chemical tracers in iron meteorites to determine the original composition of early planetesimals. These tracers, sulfur and the oxidation state of iron, indicated that matrix levels were only 8% to 17% in the original bodies. This shows that the early solar system was preferentially sorting chondrules over matrix, a process that began from the very start. The findings help explain why older chondrules are scarce in the meteorite record, as they were incorporated into bodies that later melted.

The study is published in Nature Astronomy and is led by Damanveer Grewal. Co-authors include Zhongtian Zhang and Joanna Drążkowska. The research provides the first geochemical evidence of this selective sorting process, which is crucial for understanding the formation of the solar system's first solid bodies. The findings also highlight the importance of chondrules as the basic building blocks of planets, showing that they were already being sorted and incorporated into the first generation of solid bodies from the very start.

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