Bennu is a near-Earth asteroid about 500 metres across and is widely regarded as a surviving fragment of the Solar System’s earliest building materials. NASA’s OSIRIS-REx mission collected samples from its surface in 2020 and delivered them to Earth in 2023. Laboratory studies of those samples have identified abundant carbon-bearing compounds, hydrated minerals, phosphate and other components that record interactions between rock and water. The new research focuses on a particularly distinctive component: refractory stardust. These microscopic particles, sometimes called presolar grains, condensed in the outflows of dying stars or in the debris surrounding stellar explosions. Because they formed before the Sun, they carry isotopic signatures unlike those produced by ordinary Solar System processes.

“Refractory” describes a material that remains stable at relatively high temperatures compared with more volatile substances. Presolar refractory grains can include silicon carbide, oxide and silicate minerals, depending on the type of stellar environment in which they formed. Their survival in meteorites has allowed scientists to reconstruct aspects of stellar evolution using laboratory measurements of isotopes such as carbon, nitrogen, oxygen and silicon. The grains are commonly identified through anomalous isotopic ratios: instead of matching the average composition of the Solar System, they preserve fingerprints inherited from their parent stars. Yet survival is not guaranteed. Once a grain is exposed to chemically reactive fluids, its surface can dissolve, become coated, exchange elements with the surrounding solution or be replaced by new minerals.

The study’s central chemical setting is an alkali brine, a concentrated water-based solution rich in alkaline elements and ions. On Earth, brines can form when water dissolves salts from rocks and later becomes concentrated through evaporation. Inside an asteroid, similar fluids may develop when ice melts and reacts with minerals. Alkali-rich solutions can reach high pH values, meaning they contain relatively large concentrations of hydroxide ions. Such fluids can attack silicate structures by breaking bonds between silicon and oxygen, mobilizing elements into solution and precipitating secondary minerals. The precise reaction depends on temperature, fluid composition, grain size, porosity and the duration of contact, but even modest alteration over geological timescales can transform the chemical and isotopic record of a microscopic particle.

Bennu’s minerals indicate that liquid water once circulated through its parent body, probably after radioactive heating melted internal ice. The asteroid itself is thought to have formed from fragments of a larger carbonaceous body that experienced this aqueous alteration before being disrupted by impacts. In that setting, fluids could have moved through pores and fractures, reacting with soluble salts and silicate minerals as they travelled. The result would not have been a single uniform chemical event. Instead, different regions and grains could have encountered fluids with changing pH, salinity and oxidation state. A refractory presolar grain located near an active fluid pathway might therefore have been altered much more extensively than a similar grain sealed inside a relatively dry mineral aggregate.

The word “gradual” in the study’s title is crucial. Destruction of stardust in Bennu’s brines would not necessarily resemble a sudden dissolution event. It could proceed through a sequence of surface reactions. A thin outer layer might first lose mobile elements, while the interior retains its original isotopic composition. Continued exposure could roughen the grain, generate pits and cracks, or form a chemically modified rim. Secondary minerals might then grow over the altered surface, physically isolating parts of the grain while also recording the composition of the fluid. At a sufficiently advanced stage, the original particle could be partly or entirely replaced. This stepwise progression matters because researchers examining returned samples may find not only pristine presolar grains but also damaged survivors and mineralogical traces of grains that no longer remain.

Such alteration creates a challenge for interpreting the abundance of stardust in Bennu. If fewer presolar grains are found than expected from the composition of primitive meteorites, the difference may not mean that Bennu formed from material poor in stardust. Some of the grains could have been chemically erased after accretion. Conversely, grains that remain may represent the most resistant mineral types or the portions that were protected from fluid flow. Any estimate of the original presolar inventory must therefore account for selective destruction. The researchers’ focus on alkali brines provides a mechanism by which a body can begin with an ancient stellar record and later preserve only a filtered, incomplete version of it.

The findings also connect Bennu to a broader question in planetary science: how much of an asteroid’s apparent chemical primitiveness is genuinely primordial, and how much is the product of later alteration? Primitive asteroids are not untouched time capsules. They can preserve ancient solids while simultaneously hosting reactions that modify those solids. Water can create new minerals, redistribute elements and alter organic compounds without completely erasing the original parent material. In Bennu, this dual history is especially important because returned samples permit analysis at scales from whole grains to nanometre-thick reaction layers. Electron microscopy, spectroscopy and isotope measurements can reveal whether a particle formed around another star, identify chemical zoning caused by brine exposure and distinguish original material from alteration products.

The work has implications beyond Bennu. Asteroids that contain hydrated minerals and salts may have experienced comparable episodes of internal water circulation. The chemistry of those fluids would have influenced which organic molecules survived, which minerals formed and how efficiently ancient interstellar or circumstellar material was preserved. Understanding brine-driven destruction is also relevant to the interpretation of samples from other carbon-rich bodies, including material delivered by meteorites and future returned-sample missions. Bennu’s microscopic grains are therefore more than isolated curiosities: they are probes of stellar history, asteroid geology and the chemical evolution of the Solar System. By showing that even refractory stardust can be gradually consumed by alkaline fluids, the research underscores a fundamental lesson of planetary science—ancient evidence may endure for billions of years, but it survives only through a continual contest between resistance and alteration.

Phosphorus and nitrogen, two elements fundamental to terrestrial life, play crucial roles in biological molecules and processes. The presence and relative abundance of these elements in nascent planetary bodies can provide key insights into the evolutionary pathways that led to habitable worlds. The Rice University team, led by Professor Rajdeep Dasgupta, embarked on a detailed investigation into the early chemical environment of planetesimals—the small bodies that coalesced to form planets—and how these environments influenced the availability of life-essential elements.

Central to this research was the recreation of iron meteorite formation conditions within the laboratory. Utilizing a high-pressure, high-temperature apparatus, the scientists simulated the crystallization processes that occurred within the metallic cores of these early planetesimals. Iron meteorites, which are fragments from these cores, provide an invaluable record of the primordial chemical environment, allowing researchers to reverse-engineer the elemental makeup of their parent bodies. Graduate student Debjeet Pathak, the study’s corresponding author, explained that their method involved correlating known meteorite chemical compositions with experimental results to deduce the nitrogen and phosphorus content in early planetesimals.

The solar system’s infancy, more than 4.5 billion years ago, was a dynamic milieu in which gases and dust laden with volatile compounds, including nitrogen and phosphorus, gradually coalesced into solid bodies. These small planetary embryos formed differentiated interiors, including metallic cores from which iron meteorites originated when disrupted by collisions or other cataclysmic events. The current repository of these iron meteorites largely resides in the asteroid belt, nestled between Mars and Jupiter, which acts as a dynamic boundary separating the inner terrestrial planets from the more distant gas giants.

The Rice team’s experimental approach offered unprecedented insight into the inner versus outer solar system’s chemical evolution. By simulating conditions of planetesimal formation across this spatial gradient, they observed a distinct variation in the phosphorus-to-nitrogen ratio. Inner solar system iron meteorites exhibited lower phosphorus to nitrogen ratios compared to their outer solar system counterparts. This spatial heterogeneity underscores the role of localized environmental conditions and processes in establishing the elemental inventory accessible to forming planets.

Interestingly, when the team compared these findings to the chemical signatures of chondrites—primitive, undifferentiated asteroids that formed slightly later—they found notable differences. Chondrites from the inner solar system possessed higher phosphorus-to-nitrogen ratios, which decreased progressively moving outward toward the outer solar system. This trend contrasts with the pattern found in iron meteorite-related planetesimals, suggesting distinct evolutionary timelines and mechanisms controlled element distribution during different formation epochs.

A pivotal factor influencing these disparities appears to be the massive gas giant, Jupiter. As it accrued mass and gravitational influence early in solar history, Jupiter likely acted as a formidable barrier, modulating the migration of volatile-rich materials across the nebula. This barrier would have curtailed the inward flow of nitrogen and phosphorus-bearing compounds from the outer to the inner solar system, leading to the decreasing elemental ratios observed in later chondritic bodies forming 2–3 million years after the iron meteorite parent planetesimals.

Crucially, both generations of planetesimals—those that spawned iron meteorites and those that formed chondrites—exhibited phosphorus-to-nitrogen ratios most closely aligned with the balance supporting life on Earth in the inner solar system. This convergence suggests that Earth’s life-essential elemental inventory may have predominantly originated from indigenous inner solar system sources rather than being imported from the more volatile-rich outer regions, challenging existing paradigms about planetary element delivery.

Professor Dasgupta emphasized the broader implications of these findings, stating that they offer a refined narrative on how early dust and planetesimal composition evolved under the combined influences of giant planetary growth and nebular cooling dynamics. The interplay between disk chemistry and planetary processes within the first few million years was integral to establishing the elemental framework that would foster habitable environments.

These discoveries advance our understanding of the cosmochemical processes governing planetary formation and evolution. By elucidating the distinct chemical reservoirs and transport mechanisms in the nascent solar system, this work provides foundational knowledge relevant not only to Earth’s history but also to the search for life-supporting conditions on exoplanets orbiting other stars.

The study’s fusion of experimental petrology, meteorite chemistry, and planetary formation models showcases how interdisciplinary approaches can unravel complex astrophysical phenomena. It affirms the idea that the early solar system was chemically and dynamically diverse, with primordial planetary building blocks exhibiting distinct evolutionary paths driven by both environmental and gravitational forces.

Sponsored by NASA grants 80NSSC18K0828 and 80NSSC22K0635, this research continues to position Rice University at the forefront of planetary origins and habitability studies. As the scientific community further explores these findings, the nuanced understanding of element delivery mechanisms will enrich our grasp of how indispensable ingredients for life were distributed, setting the stage for the emergence of life on Earth.

This work opens new avenues for future investigation into the timing, location, and processes that governed life-essential element synthesis and transport in the solar nebula. It also strengthens the conceptual framework guiding astrobiological exploration and the interpretation of meteoritic evidence in the context of planetary sciences. As humanity presses forward in unraveling the origins of life, studies like this illuminate the deep interconnections between cosmic evolution and biological potential.

Subject of Research: Elemental composition and formation history of early planetesimals in the solar system as revealed by phosphorus-nitrogen systematics in iron meteorites and chondrites.

Article Title: Phosphorus-nitrogen systematics of first-generation planetesimals constrain life-essential element delivery to Earth

News Publication Date: 3-Jun-2026

Web References:
https://www.science.org/doi/10.1126/sciadv.aed8749
http://dx.doi.org/10.1126/sciadv.aed8749

Keywords
Phosphorus, Nitrogen, Iron Meteorites, Chondrites, Planetesimals, Early Solar System, Elemental Ratios, Planet Formation, Jupiter, Habitability, Rice University, Solar Nebula