Djerfisherite in a Ryugu grain: A clue to localized heterogeneous conditions or material mixing in the early solar system

Djerfisherite, a K-bearing Fe-Ni sulfide, was identified in grain C0105-042 collected from the subsurface of asteroid Ryugu through SEM and TEM analyses. The mineral occurs as an isolated crystal embedded within a matrix of Mg-Fe phyllosilicates. Although djerfisherite is known to form as a condensate phase in enstatite chondrites and aubrites, its mode of occurrence in Ryugu grain C0105-042 is markedly different. Two possible origin scenarios are considered: (i) an extrinsic origin, in which a djerfisherite fragment derived from enstatite chondrites or aubrites was deposited onto asteroid Ryugu, and (ii) an intrinsic origin, where djerfisherite formed in situ through a localized reaction between K-bearing hot fluid or vapor and Fe-Ni sulfide under reducing alkaline conditions within asteroid Ryugu's body. Isotopic data, which could directly constrain its origin, are currently unavailable; thus, the origin of djerfisherite remains unresolved. Nonetheless, this finding suggests the presence of exotic material or localized chemical heterogeneities within Ryugu's body, offering new insights into the complex evolutionary processes that shaped primitive bodies in the early Solar System.