¹⁶ O poor cosmic spherules from near-Earth CY chondrite asteroids

Approximately 10% of cosmic spherules—microscopic extraterrestrial particles that melt upon atmospheric entry and dominate the influx of astromaterials to Earth—exhibit anomalous oxygen isotopic compositions, suggesting an asteroidal source not represented in current meteorite collections. We introduce a a previously unidentified subset of micrometeorites, the sulfur-rich cumulate olivine (SCumPo) cosmic spherules, characterized by cumulate textures evidencing the settling of olivine crystals, and oxygen-16 ( 16 O)–poor bulk signatures. The systematically nickel-poor olivine phenocrysts, frequent iron-nickel-sulfur droplets, unusually sulfur-rich mesostasis, and a virtual absence of magnetite all point to unusually highly reducing conditions during atmospheric entry, which may reflect unusual precursor mineralogy. Numerical modeling of olivine settling under deceleration speeds of ~14 to 17 kilometers per second suggests high-eccentricity precursor orbits ( e > 0.2), incompatible with typical main-belt asteroid sources. These findings point to a previously unsampled, primitive, sulfide-rich CY-like near-Earth asteroid, which represents a “missing” meteorite parent body that contributes distinctive 16 O-poor cosmic dust to Earth.