Bennu is an unusually accessible target for science. The asteroid completes one orbit of the Sun every 1.2 years and passes within roughly 300,000 kilometres of Earth every six years, a close approach that made it an ideal destination for a sample-return mission. NASA seized this opportunity with its OSIRIS-REx probe, which in a spectacular operation touched down on the asteroid’s surface and collected material directly from it. In 2023, the sample container descended into the Utah desert carrying around 120 grams of Bennu’s rocky payload, the largest amount of asteroid material ever returned to Earth. From that haul, a small but extraordinarily precious portion made its way to Switzerland, where Maria Schönbächler, Professor of Isotope Geochemistry at ETH Zurich, received half a gram for analysis. Her laboratory began working on the samples immediately, and the completed investigations have now yielded results that reach far beyond Bennu itself, offering new insight into how the entire Solar System took shape.

The key to the discovery lies in isotopes, atoms of the same element that differ slightly in mass because their nuclei contain different numbers of neutrons. The ETH team measured isotopes of three elements: iron, titanium and chromium. Together, these isotopic ratios create a distinctive chemical fingerprint that allows researchers to determine where a body’s raw material originated and, to some extent, how old it is. Because isotopic ratios are inherited from the cloud of dust and gas that formed the Solar System and are altered only by specific nuclear and chemical processes, they act like immutable birth certificates written into the fabric of rocks. For Bennu, that fingerprint turned out to be unlike anything scientists expected.

The measurements revealed that titanium and iron are uniformly distributed throughout the Bennu material, a sign of a remarkably well-mixed source. More striking still, the analyses showed that Bennu has close relatives scattered across the Solar System. The asteroid Ryugu, sampled by Japan’s Hayabusa2 mission, and the so-called CI meteorites, a rare class of primitive, carbon-rich rocky bodies occasionally found on Earth, all share a similar isotopic fingerprint with Bennu. This shared signature indicates that all three bodies formed from the same reservoir of cosmic dust. At the same time, the group differs significantly in isotopic composition from other known asteroids, meteorite groups and the planets, marking Bennu and its siblings out as members of a chemically distinct family with a very specific place of origin.

That place of origin is precisely where the new study overturns long-held assumptions. Until now, scientists had assumed that asteroids such as Bennu formed in the outer regions of the Solar System, possibly in the same environment where comets formed, and that they accreted relatively late in the Solar System’s evolution. The new isotope data contradict both ideas. Instead, the most likely scenario is that the birthplace of Bennu, Ryugu and the CI meteorites lay close to the water-ice line, the boundary marking the point where water vapour freezes. Around 4.5 billion years ago, as the Solar System was still taking shape, this location was a dynamic mixing zone where material from the inner and outer regions met and mingled. The ice present there acted as a kind of glue, binding the finest dust particles together into larger aggregates that would eventually grow into asteroid-sized bodies.

Bennu, in other words, is a hybrid. As Schönbächler explains, the material does not clearly match either the inner or the outer Solar System; it bears characteristics of both regions, having formed in a specific zone where flows of matter from both sides converged. This hybrid character explains several long-standing puzzles about Bennu’s composition, including why its material is so rich in water. In the vicinity of the water-ice line, ice evaporated as temperatures fluctuated, and some of the resulting water vapour condensed again in exactly the region where Bennu’s parent body formed, soaking the accumulating dust with hydrated minerals. The result is an asteroid whose substance carries the chemical memory of a boundary environment that no longer exists in the modern Solar System.

The ETH researchers and their co-authors attribute a central role in this story to Jupiter. The gas giant formed remarkably early, within roughly one million years of the Sun’s birth from a collapsing cloud of dust and gas, driven by gravitational forces within the swirling disc of material that surrounded the young star. Because it grew so rapidly, Jupiter acted as a bridge pillar within that disc: its growing bulk blocked most coarse material from crossing its orbit, while fine dust from various regions of the disc flowed around the giant planet and mixed evenly in the transition zone near the water-ice boundary. The precursors of Bennu, Ryugu and the CI meteorites subsequently accreted in this sheltered region, built almost entirely from finely intermixed dust rather than from the larger pebbles and boulders that Jupiter filtered out.

This scenario elegantly accounts for another of Bennu’s defining traits: the extraordinary chemical similarity of its material to that of the Sun itself. Because Jupiter’s protective influence ensured that Bennu formed mainly from fine dust, and because fine dust orbiting in the disc around the young Sun was thoroughly mixed, the asteroid’s composition mirrors the average Solar System inventory of elements. Schönbächler compares it to fine dust at home, which simply ends up everywhere over time. That makes Bennu an extraordinarily valuable scientific resource. It is a very primordial asteroid, and its material dates back to the birth of the Solar System around 4.5 billion years ago, having hardly changed since. As Schönbächler notes, Bennu may offer our best glimpse of the original mix of chemical elements from which the terrestrial planets were ultimately built.

The implications extend to the deepest questions about our own origins. By performing precise geochemical analyses of Bennu’s samples, researchers are refining our understanding of how the Solar System arose and under what conditions planets formed. Because the asteroid is rich in water and organic material, it also provides important pieces of the puzzle regarding how the young Earth acquired the building blocks of life, the volatile compounds and carbon-based chemistry that may have been delivered to our planet by primitive bodies like Bennu during the chaotic early era of planetary formation.

Many questions remain open. The team is now wondering whether other asteroids share the same isotopic signature as Bennu and Ryugu, and it is still unclear to what extent the young Jupiter contributed to the fact that only fine dust particles clumped together in the transition zone. Further research will help clarify this picture. Meanwhile, Schönbächler is eagerly awaiting the Japanese sample-return mission to Mars’ moon Phobos, due to launch at the end of October this year, and intends to apply to the Japanese space agency JAXA for material to analyse in her laboratory. Patience will be required, however: the capsule containing the Phobos material is not expected to return to Earth until 2031. When it does, it may allow scientists to test whether the strange hybrid fingerprint of Bennu, forged beside a growing Jupiter at the edge of the ice, was shared more widely across the early Solar System than anyone had imagined.

Subject of Research: Isotopic analysis of OSIRIS-REx samples revealing the formation origin of asteroid Bennu near the Solar System's water-ice line

Article Title: Mystery surrounding the formation of asteroid Bennu solved

Article References: Mystery surrounding the formation of asteroid Bennu solved. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: asteroid Bennu, OSIRIS-REx, isotope geochemistry, water-ice line, Jupiter, Solar System formation, Ryugu, CI meteorites, ETH Zurich, sample return, Science Advances, planet formation

The team focused on JN100, an introgression line developed by backcrossing the salt-tolerant but low-yielding Indian landrace Nona Bokra into Jupiter, a medium-grain, high-yielding Louisiana cultivar that is vulnerable to salinity. Nona Bokra carries undesirable domestication traits such as seed dormancy, shattering, and photosensitivity, but it donates genomic segments conferring tolerance. JN100 inherits those segments while retaining most of Jupiter’s agronomic background, making it an ideal system for separating tolerance-associated chemistry from ordinary genetic noise. In greenhouse experiments, seedlings of JN100, Jupiter, and Nona Bokra were exposed to salt in a stepwise protocol, first at 6 dS/m for two days and then at 12 dS/m for three days, while untreated seedlings served as controls. Leaf tissues were harvested with three biological replicates per treatment for untargeted metabolomic analysis.

The analytical core of the study was untargeted liquid chromatography-mass spectrometry performed on a Waters Synapt XS quadrupole time-of-flight instrument coupled to an Acquity Premier UPLC system at the LSU Mass Spectrometry Facility. Metabolites were separated on a hydrophilic interaction liquid chromatography amide column, an approach chosen to maximize retention of small polar compounds such as amino acids, sugars, and tricarboxylic acid cycle intermediates. Data were acquired in MSᴱ mode, with alternating low- and high-energy scans capturing both precursor ions and fragment ions across an m/z range of 100 to 1500 in positive and negative ionization modes. Features were processed in Progenesis QI, annotated against METLIN and other spectral libraries with a 10 parts-per-million mass tolerance, and reported as putative identifications under Metabolomics Standards Initiative Level 2 criteria because authentic standards were not run in-house.

Statistical treatment was deliberately stringent. Metabolites were declared differentially accumulated only when they satisfied three conditions simultaneously: a Benjamini-Hochberg false-discovery-rate-adjusted p-value below 0.05, a fold change of at least 1.5, and a variable importance in projection score greater than 1 from an orthogonal partial least squares discriminant analysis model. This supervised model cleanly separated genotypes and treatments, with the predictive score explaining 79.7 percent of class-discriminating variance under control conditions and 91.2 percent under salt stress. Post hoc power analysis confirmed that all significant differences exceeded a power of 0.8, lending statistical weight to the biological patterns that emerged.

Those patterns were striking. In the JN100-Jupiter comparison under salt stress, the team identified 201 differentially accumulated metabolites, 89 upregulated and 112 downregulated, spanning amino acids, carbohydrates, fatty acids, purines, pyrimidines, and numerous other chemical classes. Several compounds stood out as signature markers of tolerance. Glycitin, an isoflavone, was present at roughly 20-fold higher levels under control conditions and 25-fold higher under salt stress in JN100, and it was entirely undetectable in Jupiter when the cultivars were analyzed individually under salinity. D-arabinono-1,4-lactone, a precursor in ascorbic acid biosynthesis, accumulated 23-fold more under salt stress, while the sugar alcohol ribitol rose 19-fold. Because ascorbate is a central antioxidant that detoxifies reactive oxygen species, the enrichment of its precursor suggests that JN100 boosts its capacity to neutralize the oxidative burst that accompanies salt exposure.

Equally telling were the metabolites that declined. Violanthin, a flavonoid glycoside, dropped 24-fold under salt stress, and rutin, another antioxidant flavonoid, fell by a similar margin with a VIP score above 1 only under stress, indicating a stress-specific metabolic shift. L-methionine S-oxide, an oxidized methionine derivative that serves as a substrate for methionine sulfoxide reductases, decreased 20-fold, which the authors interpret as evidence of more efficient enzymatic repair of oxidized proteins in the tolerant line. Allantoin, a purine catabolism product known to activate jasmonate signaling, was also reduced, suggesting that JN100 avoids the excessive jasmonate activation and programmed cell death that can follow unchecked stress signaling. Lysine fell 21-fold, pointing to active redistribution of nitrogen away from storage amino acids toward stress-protective pathways.

Pathway enrichment analysis in MetaboAnalyst using rice-specific KEGG pathways revealed the systemic logic behind these individual changes. Arginine biosynthesis and the metabolism of alanine, aspartate, and glutamate were the most significantly enriched pathways in the tolerant-versus-susceptible comparison under salt, with impact scores of 0.494 and 0.787 respectively. Purine metabolism, the pentose phosphate pathway, glutathione metabolism, and glyoxylate and dicarboxylate metabolism were also enriched, indicating that salt tolerance in JN100 rests on coordinated reprogramming of nitrogen assimilation, redox buffering, and energy metabolism. The susceptible parent Jupiter showed its own perturbations in arginine biosynthesis and amino acid metabolism, but Nona Bokra and JN100 displayed patterns emphasizing antioxidant defense and osmoprotection, consistent with the tolerance they share.

To connect chemistry with genetics, the researchers integrated these metabolomic profiles with differentially expressed genes from their earlier transcriptomic study of JN100, using joint pathway analysis and the STITCH gene-chemical interaction database. Ten differentially expressed genes mapped onto the metabolite network with high confidence, with combined interaction scores ranging from 0.998 to 0.999. Three glutamate synthase genes, OsGLT1, OsGLT2, and OsFd-GOGAT, formed the network’s hub, each interacting with more than a dozen metabolites of nitrogen assimilation and the TCA cycle, including glutamate, glutamine, alpha-ketoglutarate, aspartate, and reduced glutathione. Two paralogs, OsP5CS1 and OsP5CS2, which channel glutamate into proline biosynthesis, connected this nitrogen module to osmotic adjustment, since proline acts as an osmoprotectant, membrane stabilizer, and radical scavenger. OsNAGS2, which catalyzes the committed step of arginine biosynthesis, and OsDHQDT/SDH, a shikimate pathway enzyme linking carbon metabolism to aromatic amino acid and flavonoid production, completed the picture, alongside a phenylalanyl-tRNA synthetase and a pyridoxal phosphate-dependent transferase involved in cofactor metabolism.

The integrated model that emerges is one of coordinated metabolic plasticity. Shikimate-derived carbon appears to be selectively routed toward the accumulating isoflavone glycitin rather than toward the declining flavonoid glycosides violanthin and rutin, while methionine repair, NAD cofactor turnover signaled by nicotinamide ribotide, and purine catabolism converge on redox homeostasis. Nitrogen freed from lysine catabolism feeds the glutamate-proline-arginine axis, where the P5CS and GOGAT enzymes, sensitive to salt-induced disruption in susceptible plants, remain active in JN100. The authors are careful to note that these gene-metabolite associations are correlative: no transcription factors appeared in the mapping, and establishing causal regulation will require chromatin immunoprecipitation, transactivation assays, gene editing, and metabolic flux analysis. Even so, the study delivers a concrete set of metabolite markers, including glycitin, D-arabinono-1,4-lactone, and ribitol, and candidate genes, including OsP5CS1, OsFd-GOGAT, and OsDHQDT/SDH, that breeders and biotechnologists can now pursue to engineer rice capable of thriving where salt once meant failure.

Subject of Research: Metabolomic mechanisms of salinity tolerance in a rice introgression line

Article Title: Comparative metabolomic profiling reveals salinity tolerance mechanisms in a rice introgression line

Article References: Chaudhary, C. K., Guttula, P. K., Agrawal, K., Subudhi, P. K., & Gartia, M. R. (2026). Comparative metabolomic profiling reveals salinity tolerance mechanisms in a rice introgression line. Metabolomics, 22(5), Article 149. https://doi.org/10.1007/s11306-026-02525-2

Image Credits: AI Generated

DOI: 10.1007/s11306-026-02525-2

Keywords: rice, salinity tolerance, metabolomics, introgression line, Nona Bokra, Jupiter, glycitin, proline biosynthesis, redox homeostasis, nitrogen metabolism, LC-MS, abiotic stress