Through pristine samples returned by Hayabusa2 on December 6, 2020, scientists have uncovered a mineral on asteroid Ryugu that shouldn’t be there, upending assumptions about the building blocks of our Solar System. In a paper published May 28, 2025, in Meteoritics & Planetary Science, a team at Hiroshima University reports finding djerfisherite, a potassium‑bearing iron‑nickel sulfide, embedded in a grain from the carbon‑rich C‑type asteroid.
Ryugu’s rocks closely resemble CI chondrite meteorites, which formed in watery environments and stayed relatively cool, never exceeding about 50°C. Those conditions should preclude the formation of djerfisherite, which until now has only been seen in the highly reduced interiors of enstatite chondrites.
“Djerfisherite is a mineral that typically forms in very reduced environments, like those found in enstatite chondrites, and has never been reported in CI chondrites or other Ryugu grains,” says Masaaki Miyahara, associate professor at Hiroshima University.
Miyahara’s team was investigating how Earth’s atmosphere might have altered Ryugu grains when they turned to field‑emission transmission electron microscopy (FE‑TEM). While scanning grain C0105‑042 from sample plate C0105‑042, they spotted an isolated crystal of djerfisherite surrounded by magnesium‑iron phyllosilicates.
“The discovery of djerfisherite in a Ryugu grain suggests that materials with very different formation histories may have mixed early in the solar system’s evolution, or that Ryugu experienced localized, chemically heterogeneous conditions not previously recognized,” Miyahara elaborates.
Asteroid Ryugu is believed to be part of a larger parent body that formed 1.8 to 2.9 million years after the Sun ignited. In its outer‑solar‑system birthplace, ice and rock mixed until heat from radioactive decay melted the ice, but temperatures likely stayed below 50°C. In contrast, enstatite chondrite bodies formed closer to the Sun, where high‑temperature gases or potassium‑rich fluids heated rocks above 350°C—conditions thought necessary for djerfisherite to crystallize.
To explain the presence of this exotic mineral on Ryugu, the team proposes two scenarios: an extrinsic origin, in which djerfisherite fragments were delivered from more reduced asteroids; or an intrinsic origin, where localized reactions between hot, potassium‑bearing fluids or vapors and iron‑nickel sulfides forged the mineral in situ when parts of Ryugu briefly heated above 350 °C.
Preliminary analyses tip the balance toward the intrinsic hypothesis. The next step is to conduct isotopic studies on this grain and others, which could reveal whether the mineral’s atoms match Ryugu’s typical composition or point to an external source.
The study has been published in Meteoritics & Planetary Science.
