An unexpected Ryugu mineral is forcing scientists to rethink how the earliest asteroids formed and evolved. A potassium-bearing Fe–Ni sulfide called djerfisherite has been identified in a single Ryugu grain and, crucially, it typically forms at temperatures above 350°C—conditions long thought incompatible with the famously “cold and wet” histories of CI chondrites like Ryugu. The finding, from a mission that returned just 5.4 grams of material, points to either localized heating or early Solar System mixing, and it could rewrite parts of planetary formation timelines.

Key Takeaways

– shows a >350°C formation signal in a CI-type sample, as djerfisherite appears in Ryugu grain C0105-042, contradicting low-temperature alteration expectations. – reveals Hayabusa2 delivered 5.4 grams of Ryugu material on December 6, 2020, enabling laboratory confirmation of the high-temperature mineral in grain no. 15. – demonstrates sample C0105-042’s composition is heterogeneous, implying either transport from hotter inner regions or in-situ heating above 350°C on the parent body. – indicates Ryugu’s parent body assembled 1.8–2.9 million years after Solar System birth, tightening the window for early mixing and thermal events. – suggests non-invasive X-ray methods at two NSLS-II beamlines (XFM, TES) and 2024 phosphate detections frame a multi-stage fluid and thermal history.

Why the Ryugu mineral discovery defies expectations

The detection of djerfisherite in Ryugu grain number 15 (sample plate C0105-042) is startling because CI chondrites are the most chemically primitive meteorites and are typically altered at low temperatures by water, not forged in high-temperature regimes. Lead author Masaaki Miyahara likened the result to “finding a tropical seed in Arctic ice,” underscoring how out of place a >350°C signal is in such material. The team notes the mineral had not been reported in CI chondrites before this study, making the case especially compelling [1].

Djerfisherite’s presence points to compositional heterogeneity within Ryugu’s parent body material. That heterogeneity may reflect a mix of primordial building blocks or transient heating pockets that briefly raised temperatures far above the limits usually associated with CI chondrite alteration. Either scenario weakens the long-standing assumption that CI-type bodies experienced only gentle, low-temperature aqueous processing and little high-temperature overprint.

The 5.4 g cache: what it tells us and how it arrived

Hayabusa2 returned 5.4 grams of Ryugu material to Earth on December 6, 2020, providing pristine samples for laboratory analysis that cannot be replicated by meteorite falls contaminated on Earth. In a June 2025 summary, researchers laid out two main hypotheses to explain djerfisherite in a CI sample: transport of hot inner Solar System material to the outer asteroid, or intrinsic formation within Ryugu’s parent body at temperatures greater than 350°C. The paper (DOI 10.1111/maps.14370) notes isotopic work is planned to test these models [2].

Both hypotheses carry testable predictions. If inner Solar System transport seeded the grain, isotopic fingerprints may skew toward reservoirs associated with hotter, metal- and sulfide-forming environments. If localized heating within the parent body is responsible, textures, diffusion profiles, and co-located alteration phases could preserve a thermal gradient and time sequence consistent with short-lived, internal heat pulses rather than wholesale importation of exotic material.

Timelines that constrain the origin

Chronology further tightens the interpretive window. Independent reporting places Ryugu’s parent body assembly at roughly 1.8–2.9 million years after the Solar System’s origin—early enough for energetic mixing and transient heat sources to still be active. Djerfisherite’s typical formation either from high-temperature gas or hydrothermal reactions above 350°C clashes with the uniform, low-temperature narrative for CI chondrites and instead implies a planetesimal environment punctuated by heterogeneity in both chemistry and temperature [3].

That timing aligns with recognized periods of vigorous radial transport of dust and pebbles, as well as potential heat from short-lived radionuclides and shock events. The mineral’s occurrence in just one identified grain so far does not limit its significance; in rare-material studies, even single-grain evidence can anchor models for early Solar System dynamics when the thermodynamic constraints are strong.

How scientists probed the Ryugu mineral without breaking it

Even before this high-temperature find, beamline experiments on Ryugu samples had signaled a complex alteration history. Using the National Synchrotron Light Source II (NSLS‑II), researchers applied pink‑beam fluorescence computed tomography and tender‑energy X-ray absorption spectroscopy at the XFM and TES beamlines to map elements such as phosphorus, sulfur, selenium, and iron in situ. The non-invasive workflow preserved samples while identifying a rare phosphide and suggesting multiple stages of fluid alteration within Ryugu materials [4].

These non-destructive approaches are essential because pristine extraterrestrial grains are scarce and irreplaceable. By combining 3D fluorescence imaging with energy-tuned spectroscopy, teams can locate sub-grain microenvironments—sulfidic, phosphatic, or otherwise—that record distinct redox and thermal episodes. That context is critical for interpreting why a >350°C phase appears adjacent to minerals emblematic of low-temperature aqueous alteration, and it helps design targeted follow-up measurements without consuming the sample.

Beyond sulfides: phosphorus minerals complicate the story

A 2024 peer-reviewed study used similar NSLS‑II techniques to report hydrated ammonium magnesium phosphate (HAMP) and hydroxyapatite in Ryugu material, expanding the catalog of water-related minerals and hinting that phosphorus speciation on small bodies may have shaped early organic chemistry. The work emphasized that these phosphates could have influenced prebiotic phosphorus availability on early Earth, and, more broadly, they reinforce that Ryugu’s record includes multiple, distinct stages of fluid processing [5].

This phosphate evidence dovetails with the new sulfide result: Ryugu’s rocky history appears to weave together water-mediated alteration with episodes capable of crossing the >350°C threshold. That blend might reflect a patchwork parent body where fluids circulated through some zones while others experienced thermal spikes—whether via internal heat, impacts, or imported hot grains—before the material agglomerated into the rubble-pile asteroid explored by Hayabusa2.

Why the Ryugu mineral discovery defies expectations

For decades, CI chondrites were cast as chemical yardsticks for the Solar System—primitive, aqueously altered, and largely devoid of high-temperature overprint. Finding djerfisherite flips that simplicity on its head. Because this phase prefers hotter conditions, its occurrence implies either that Ryugu’s source material was more diverse than assumed or that the parent body experienced unrecognized thermal regimes. Either way, the Ryugu mineral discovery injects temperature—and therefore energy—back into the storyline for at least part of the CI spectrum.

The consequences extend beyond taxonomy. If small bodies like Ryugu carry both low-temperature aqueous signatures and high-temperature mineralogies, then the pathways that delivered volatiles and prebiotic ingredients to early Earth could have been punctuated by thermal episodes that altered mineral catalysts, redox states, and phosphorus availability. Understanding the exact sequence and scale of heating versus hydration now becomes central to modeling which combinations best fostered prebiotic chemistry.

How scientists probed the Ryugu mineral without breaking it

Methodology will decide how quickly this puzzle resolves. The same non-invasive X-ray toolset that revealed phosphates and phosphides—3D fluorescence CT and tender-energy spectroscopy—can be tuned to locate sulfide-rich microdomains and determine their spatial relationships to hydrated phases. Combined with micro-focused diffraction and microprobe analyses, researchers can build a voxel-by-voxel map of temperature and fluid history for grain C0105-042 and neighboring fragments without exhausting the precious sample.

Future isotopic measurements, already planned by the reporting team, could discriminate between imported inner Solar System material and in-situ heating on the parent body. Signatures in elements sensitive to temperature histories, when cross-referenced with textural evidence and the presence or absence of secondary alteration halos, will constrain whether the >350°C phase formed locally or represents a transported relic from a hotter neighborhood closer to the Sun.

Timelines, tests, and the road ahead

What would decisively favor the “import” scenario? A strong isotopic offset from typical CI matrices aligned with reservoirs known for high-temperature sulfide formation, plus textural sharpness consistent with foreign-grain encapsulation. In contrast, clear evidence of reaction rims, fluid-mediated recrystallization, or diffusion gradients into adjacent CI-like material could argue for localized thermal events on Ryugu’s parent body after assembly.

Critically, both scenarios must fit within the 1.8–2.9 million-year assembly window and the broader cadence of early Solar System transport and heating. The djerfisherite result encourages teams to resurvey other Ryugu grains systematically and to revisit CI chondrite collections with higher-resolution, non-destructive workflows. If additional >350°C indicators appear—even sporadically—it would cement the case for CI heterogeneity and reframe how “primitive” materials record early planetary processes.

Sources:

[1] Hiroshima University – An unexpected mineral in a Ryugu grain: www.hiroshima-u.ac.jp/en/news/90759″ target=”_blank” rel=”nofollow noopener noreferrer”>https://www.hiroshima-u.ac.jp/en/news/90759

[2] ScienceDaily (Hiroshima University) – A mysterious mineral in asteroid Ryugu may rewrite planetary history: www.sciencedaily.com/releases/2025/06/250627234111.htm” target=”_blank” rel=”nofollow noopener noreferrer”>https://www.sciencedaily.com/releases/2025/06/250627234111.htm [3] Phys.org – Unexpected mineral in a Ryugu grain challenges paradigm of the nature of primitive asteroids: https://phys.org/news/2025-06-unexpected-mineral-ryugu-grain-paradigm.html

[4] Brookhaven National Laboratory / Newswise – Ryugu Asteroid Research Reveals Mineral History Predating Any on Earth: www.newswise.com/articles/ryugu-asteroid-research-reveals-mineral-history-predating-any-on-earth” target=”_blank” rel=”nofollow noopener noreferrer”>https://www.newswise.com/articles/ryugu-asteroid-research-reveals-mineral-history-predating-any-on-earth [5] OSTI / Geosciences – Chemistry in Retrieved Ryugu Asteroid Samples Revealed by Non-Invasive X-Ray Microanalyses: www.osti.gov/biblio/2367443″ target=”_blank” rel=”nofollow noopener noreferrer”>https://www.osti.gov/biblio/2367443

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