Nature, formation, and distribution of carbonates on Ceres

摘要

Different carbonates have been detected on Ceres, and their abundance and spatial distribution have been mapped using a visible and infrared mapping spectrometer (VIR), the Dawn imaging spectrometer. Carbonates are abundant and ubiquitous across the surface, but variations in the strength and position of infrared spectral absorptions indicate variations in the composition and amount of these minerals. Mg-Ca carbonates are detected all over the surface, but localized areas show Na carbonates, such as natrite (Na₂CO₃) and hydrated Na carbonates (for example, Na₂CO₃·H₂O). Their geological settings and accessory NH₄-bearing phases suggest the upwelling, excavation, and exposure of salts formed from Na-CO₃-NH₄-Cl brine solutions at multiple locations across the planet. The presence of the hydrated carbonates indicates that their formation/exposure on Ceres’ surface is geologically recent and dehydration to the anhydrous form (Na₂CO₃) is ongoing, implying a still-evolving body.