First solar system worlds formed from rock, not ice
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Scientists at Yale University uncovered the earliest chemical evidence showing that the building blocks of planets in the solar system sorted themselves by composition within its first million years.
The research team analysed iron meteorites to reconstruct the makeup of planetesimals, early, solid bodies that eventually formed planets. These planetesimals contained melted material, but preserved chemical traces revealed they originally held a surprisingly low amount of icy dust, known as matrix.
Researchers used sulfur and iron oxidation as tracers to determine the original proportions of chondrules, millimeter-sized rock beads, and matrix. Both tracers indicated that early planetesimals were composed of only 8% to 17% matrix, much less than found in later-forming meteorites. This suggests that the process of assembling these early bodies favored rocky materials over icy ones from the very beginning.
The team’s findings extend our understanding beyond what previous studies of carbonaceous chondrites, primitive meteorites containing water and organic compounds, could reveal. These earlier planetesimals were built from 83% to 92% chondrules, demonstrating a selective assembly process. By studying chondrites, which haven’t undergone complete melting, scientists can directly examine materials from this ancient period of planet formation.
