A new study has identified a fundamental difference between the asteroid samples returned to Earth from Ryugu and Bennu and the meteorites that have traditionally served as the main source of information about the early Solar System. The research, published in Nature Communications, reports that both carbon-rich asteroids preserve primordial isotopic heterogeneity—a chemical unevenness inherited from the Solar System’s birth—that appears to have been erased, blurred, or overlooked in the meteorite record. The finding offers scientists a new way to investigate the material from which planets formed and suggests that the Solar System may have been chemically more diverse at its beginning than laboratory collections have indicated.
Isotopes are atoms of the same element that contain different numbers of neutrons. They behave almost identically in ordinary chemical reactions, but their subtle mass differences and radioactive histories make them powerful tracers of cosmic events. Some isotopic patterns were created in ancient stars before the Sun existed, while others emerged from radioactive decay or nuclear reactions in the young Solar System. Because these signatures can survive for billions of years, scientists use them as fingerprints to determine where planetary material formed, how it moved through the protoplanetary disk, and whether apparently similar objects actually came from distinct reservoirs.
The study focuses on samples from Ryugu and Bennu, two dark, carbon-rich near-Earth asteroids explored by Japan’s Hayabusa2 mission and NASA’s OSIRIS-REx mission. Unlike ordinary meteorites, which have passed through Earth’s atmosphere and often experienced heating, contamination, fragmentation, and prolonged terrestrial weathering, returned asteroid samples are collected, sealed, and analyzed under carefully controlled conditions. That difference is scientifically crucial. Meteorites provide an invaluable but selective archive: only material strong enough to survive ejection from an asteroid, travel through space, enter Earth’s atmosphere, and remain recognizable on the surface becomes part of the collection. Fragile and chemically unusual materials may be missing before scientists ever examine them.
According to the researchers, the Ryugu and Bennu samples retain isotopic variations that are not readily visible in conventional meteorite groups. These differences indicate that the parent materials of the two asteroids, and perhaps the broader region from which they originated, were not chemically uniform. Instead, the early Solar System contained multiple reservoirs with distinct isotopic compositions. Such reservoirs may have formed from dust and grains inherited from different stellar sources or may have developed as material was separated, transported, and mixed within the disk of gas and dust surrounding the newborn Sun.
This result challenges a long-standing assumption behind many models of planetary formation: that the meteorites available on Earth adequately represent the full range of primitive material that existed in the Solar System. Meteorite classification has traditionally relied on recognizable chemical and mineralogical features, and many meteorites do preserve ancient components with remarkable clarity. Yet the new evidence suggests that the surviving meteorite population may be biased toward certain types of parent bodies and geological histories. Processes such as aqueous alteration, thermal metamorphism, impact fragmentation, and atmospheric entry can modify or destroy the very isotopic contrasts that researchers are trying to measure.
The importance of isotopic heterogeneity extends beyond the classification of asteroids. Planetary scientists use differences in isotopic composition to reconstruct the architecture of the protoplanetary disk, including the movement of solids across large distances. If materials formed in different parts of the disk retained distinct isotope signatures, those signatures can reveal whether early planetary building blocks remained isolated or were mixed by powerful transport processes. They can also help test competing explanations for the separation between inner and outer Solar System materials, a division reflected in the compositions of rocky planets, primitive asteroids, and the giant planets’ smaller remnants.
Ryugu and Bennu are especially valuable because they are considered primitive bodies: their bulk compositions and mineral assemblages preserve evidence of processes that occurred before, or during, the earliest stages of planetary assembly. Both asteroids contain carbon-bearing material and minerals that interacted with water inside their parent bodies. Their samples therefore provide a layered record. Some components may predate the Sun, while others formed after the Solar System emerged. Untangling these histories requires high-precision measurements capable of distinguishing inherited nucleosynthetic signatures from changes caused by radioactive decay, chemical alteration, or later processing. The new study’s central message is that the returned samples contain information that can be difficult or impossible to recover from meteorites alone.
The discovery also highlights why sample-return missions have become a turning point in planetary science. Remote observations can determine an asteroid’s color, reflectivity, shape, and surface mineral signals, but they cannot fully resolve microscopic isotope distributions. Laboratory analysis, by contrast, can measure variations at extremely small scales and compare them with reference materials from Earth and meteorite collections. Every grain can be examined for its elemental abundances, mineral structure, organic compounds, and isotopic ratios. Because the samples from Ryugu and Bennu were collected directly from their asteroids and protected from extensive terrestrial exposure, they allow researchers to test whether patterns seen in meteorites are universal or merely the result of sampling bias.
The findings may force scientists to revise how they connect meteorite groups to asteroid families and how they estimate the composition of the material that built the planets. A meteorite that appears representative of a primitive asteroid may instead record only a narrow portion of its parent body’s chemical diversity. Conversely, isotopic signatures preserved in Ryugu and Bennu could help identify links between returned samples, meteorites, and distant populations of asteroids that previously seemed unrelated. Future work will likely compare these measurements with samples from other missions, including material returned from different regions of the Moon and, eventually, Mars. Each new collection could reveal another missing piece of the Solar System’s chemical map.
For now, the study presents Ryugu and Bennu as time capsules of a more varied cosmic environment than the meteorite record alone had suggested. Their isotopic heterogeneity preserves traces of the raw ingredients that existed before planets, moons, and asteroids settled into their modern forms. The result does not make meteorites obsolete; instead, it shows that they are one part of a much larger and more selective archive. By combining meteorite analyses with pristine asteroid samples, scientists can begin to distinguish the original structure of the Solar System from the alterations imposed by billions of years of geological and atmospheric history. What looks like uniformity in Earth’s collections may, in fact, be the residue of a far more diverse beginning.
Subject of Research: Primordial isotopic heterogeneity preserved in samples from the asteroids Ryugu and Bennu, and its significance for understanding the early Solar System.
Article Title: Ryugu and Bennu preserve primordial isotopic heterogeneity absent from the meteorite record.
Article References: Bizzarro, M., Schiller, M., van Kooten, E. et al. “Ryugu and Bennu preserve primordial isotopic heterogeneity absent from the meteorite record.” Nature Communications (2026). https://doi.org/10.1038/s41467-026-76720-z
Image Credits: AI Generated
DOI: 10.1038/s41467-026-76720-z
Keywords: Ryugu, Bennu, asteroid samples, isotopes, primordial Solar System, meteorites, planetary formation, sample-return missions, cosmochemistry, isotopic heterogeneity
