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Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres

2015; Nature Portfolio; Volume: 528; Issue: 7581 Linguagem: Inglês

10.1038/nature16172

1476-4687

M. C. De Sanctis, E. Ammannito, A. Raponi, S. Marchi, T. B. McCord, H. Y. McSween, F. Capaccioni, M. T. Capria, F. G. Carrozzo, M. Ciarniello, A. Longobardo, F. Tosi, S. Fonte, V. Formisano, A. Frigeri, M. Giardino, G. Magni, E. Palomba, D. Turrini, F. Zambon, J. Ph. Combe, W. C. Feldman, R. Jaumann, L. A. McFadden, C. M. Pieters, T. H. Prettyman, Michael J. Toplis, C. A. Raymond, C. T. Russell,

Isotope Analysis in Ecology

Infrared spectra of (1) Ceres acquired at distances of 82,000 to 4,300 kilometres from the surface indicate widespread ammoniated phyllosilicates; the presence of ammonia suggests that material from the outer Solar System was incorporated into Ceres. The VIR spectrometer onboard NASA's Dawn spacecraft has obtained infrared spectra of the dwarf planet Ceres at distances of 82,000 to 4,300 kilometres and at wavelengths of 0.4–5 μm, including the 2.6–2.9 μm spectral region not accessible to Earth-bound telescopes due to atmospheric absorption. The data indicate the widespread presence of ammoniated phyllosilicates across the asteroid's surface. No water ice could be detected, though small localized occurrences of water ice cannot be excluded. The discovery of ammonia implies that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt. Studies of the dwarf planet (1) Ceres using ground-based and orbiting telescopes have concluded that its closest meteoritic analogues are the volatile-rich CI and CM carbonaceous chondrites1,2. Water in clay minerals3, ammoniated phyllosilicates4, or a mixture of Mg(OH)2 (brucite), Mg2CO3 and iron-rich serpentine5,6 have all been proposed to exist on the surface. In particular, brucite has been suggested from analysis of the mid-infrared spectrum of Ceres6. But the lack of spectral data across telluric absorption bands in the wavelength region 2.5 to 2.9 micrometres—where the OH stretching vibration and the H2O bending overtone are found—has precluded definitive identifications. In addition, water vapour around Ceres has recently been reported7, possibly originating from localized sources. Here we report spectra of Ceres from 0.4 to 5 micrometres acquired at distances from ~82,000 to 4,300 kilometres from the surface. Our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. Ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on Ceres during differentiation. This suggests that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt.