During the Solar System’s first million years, its earliest outer worlds formed from material that was up to 92 percent heat-forged rock, while gas flowing through the young system filtered out much o
A new study of carbonaceous iron meteorites reveals that the earliest outer Solar System planetesimals were composed primarily of heat-forged rock rather than volatile-rich material. This finding suggests that selective planet building occurred within the first million years of the Solar System's formation.
Why it matters
This research challenges previous assumptions about the composition of early planetary building blocks and refines our understanding of the Solar System's formative processes.
Two chemical tracers in carbonaceous iron meteorites indicate that the earliest outer Solar System planetesimals contained only 8 to 17 percent fine matrix, extending aerodynamic sorting to the opening era of planet formation.
Published September 20, 2026 · How we edit
The first solid worlds assembled in the outer Solar System did not simply collect a representative scoop of everything around them. A new analysis of carbonaceous iron meteorites indicates that their parent planetesimals contained only 8 to 17 percent fine, volatile-rich matrix. The rest, as much as 92 percent by mass, was dominated by millimetre-scale rocky particles called chondrules that had been intensely heated before they cooled.
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