Study finds earliest solar system bodies were built almost entirely from heat-formed rock, not icy dust

By the Everything Space news desk · 18 Sep 2026 · written from the sources below

Image: Phys.org

New chemical evidence shows planet-building material was being selectively sorted within the solar system's first million years, far earlier than previously documented.

Researchers have found the earliest evidence yet that the young solar system favored heat-forged rocky grains called chondrules over icy, dust-rich material called matrix when building its first solid bodies. The study indicates that this sorting process was already underway within the first million years of the solar system's formation, far earlier than the 2-4 million year timeframe established by previous research.

The team, led by a Yale researcher, examined iron meteorites originating from the outer solar system. These meteorites came from planetesimals that absorbed so much radioactive aluminum-26 that they melted entirely, wiping out physical evidence of their original composition. To get around this, the researchers used chemical tracers linked to matrix content: sulfur, which concentrates in matrix material, and the oxidation state of iron, which reflects how much water ice and oxidized dust was originally present.

Both tracers pointed to the same conclusion independently, giving the researchers confidence in the result. The calculations showed the original bodies contained only a small fraction of matrix material, less than what has been observed in any known chondrite meteorites, meaning these early planetesimals were overwhelmingly composed of chondrules.

This matrix-poor, chondrule-rich composition helps explain why very old chondrules are rarely found in the meteorite record. Rather than being lost, the researchers propose these chondrules were folded into planetesimals that later melted, destroying the physical traces while leaving behind the chemical fingerprints identified in the study.

The findings extend understanding of how the raw ingredients of planets, moons and other bodies were selected and organized from the solar system's very earliest stages, showing that the preference for heat-processed rock over icy dust was a foundational feature of planet formation rather than something that emerged later.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.