RESUMEN
The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres' surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 µm. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.
RESUMEN
The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud.
