The mystery of the missing mantle problem and insights from spectroscopy

Differentiation of planetesimals results in the segregation of materials, with the densest materials sinking, producing a metallic core, while the lighter fraction, rises, fabricating a crust. While there are multiple examples of planetary crusts (e.g., V-type asteroids) and metallic cores (e.g., M-type asteroids), there appears to be a scarcity of mantle-like materials in both the asteroid (e.g., A-type asteroids) and meteorite record. This lack of olivine-dominated material has been dubbed ‘The Missing Mantle Problem’. Here we measure the reflectance spectra of four olivine-rich meteorites expected to originate from the mantle of differing planetesimals. Following the Bus-DeMeo taxonomy, NWA 12264 and Chassigny can be classified as Sa-types, while NWA 8535 and NWA 15717 are classified as Q-types. This result implies that mantle-like materials are not restricted to A-type asteroids as previously expected. This study provides a significant step toward the resolution of the apparent shortage of olivine-rich material in the early Solar System.