The young Solar System resembled a giant construction site: around the newborn Sun swirled a disk of gas and dust, and from this dust gradually assembled stones, boulders, and then planetary embryos — planetesimals. Today, their fragments fall to Earth as meteorites. By composition, meteorites fall into two big families: they once formed on opposite sides of an invisible barrier in the disk — likely near the orbit of the future Jupiter.
To determine when the birth of these bodies began, the authors built a refined model of their thermal history. It included chemical reactions and phase transitions during heating, as well as natural variations in composition. It turned out that the parent bodies of iron meteorites from both groups — the “inner” and the “outer”—began forming almost simultaneously, roughly 0.95 million years after the appearance of the first solid particles (the so-called CAIs — calcium-aluminum-rich inclusions). In contrast, the parent bodies of stony meteorites, chondrites, were born later and at different times for different groups.
By comparing the ages with the proportions of isotopic “signatures” in meteorites, the scientists reconstructed the motion of material through the disk. They found that the material from both groups began crossing the barrier exactly when planetesimal formation started. It seems that the same event both triggered the birth of planetary embryos and opened a “gate” for mixing. What that phenomenon was remains unclear, but now its traces can be sought in models of disk evolution. Thus, meteorites that fell to Earth billions of years later help us reconstruct the first steps of our planetary system.
as written by the authors arXiv:2602.17367
The formation of planetesimals was an integral part of the cascading series of processes that built the terrestrial planets. To illuminate planetesimal formation, here we develop a refined thermal evolution model to calculate the formation ages of meteorite parent planetesimals. This model includes chemical reactions and phase changes during heating, as well as natural variations in the proportions of the constituent phases of these planetesimals. We find that the parent bodies of non-carbonaceous (NC) and carbonaceous (CC) iron meteorites start forming at very similar times (~0.95 Myr after calcium-aluminium-rich inclusion [CAI] formation) and occupy overlapping time windows. NC and CC chondrite parent bodies formed later during non-overlapping periods. We combine these ages with proportions of isotopic end-members we recover from mixing models to construct records of motion throughout the protoplanetary disk. These records argue that NC and CC material traversed the barrier in the disk after ~0.95 Myr after CAI formation. The onset of this motion coincided with planetesimal formation, indicating that the phenomenon that drove motion also triggered planetesimal formation. We argue that this feature also served as the semi-permeable barrier in the disk. Although its identity is uncertain, the effects this phenomenon had on the timing of planetesimal formation and motion through the disk can now serve as constraints on models of disk evolution. Models that reproduce these effects would elucidate the nature and implications of this phenomenon, which is key to unlocking a holistic model of terrestrial planet building.
Iron meteorites are fragments of the cores of ancient planetesimals that managed to melt and separate into a metallic core and a rocky mantle before being destroyed.
In Arthur C. Clarke's novel Rendezvous with Rama, humanity encounters an object that came from the depths of space — much like meteorites bring us material that traveled through the entire young Solar System.