The surface and internal structure of Ceres show evidence of a global process of aqueous alteration, indicating the existence of an ocean in the past. However, it is not clear whether part of this ocean is still present and whether residual fluids are still circulating in the dwarf planet. These fluids may be exposed in a geologically young surface, and the most promising site to verify the occurrence of present fluids on Ceres is Cerealia Facula dome, in Occator crater. This very young facula exhibits minerals that are relatively rare in our Solar System, the formation of which requires the presence of liquid water in combination with hydrothermal activity. Here we report the discovery of hydrated sodium chloride on Cerealia Facula. These newly identified chloride salts are concentrated on the top of the dome, close to a system of radial fractures. The spatial distribution of the hydrated phase suggests that chloride salts are the solid residue of deep brines that reached the surface only recently, or are still ascending. These salts are very efficient in maintaining Ceres’s warm internal temperature and lowering the eutectic temperature of the brines, in which case ascending salty fluids may exist in Ceres today.
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Dawn data are archived in NASA’s Planetary Data System. VIR spectral data may be obtained at https://sbn.psi.edu/pds/resource/dawn/dwncvirL1.html.
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We thank E. C. Thomas, T. H. Vu, R. Hodyss, P. V. Johnson and M. Choukroun for providing the spectra of the fast frozen brines. We thank M. Zolotov for the discussion about the dehydration rate of hydrohalite. We thank M. Sori for helpful comments. We also thank the Dawn Mission Operations team and the Framing Camera team. The VIR was funded and coordinated by the Italian Space Agency and built by Leonardo (Italy), with the scientific leadership of the Institute for Space Astrophysics and Planetology, Italian National Institute for Astrophysics, Italy, and is operated by the Institute for Space Astrophysics and Planetology, Rome, Italy. This work has been supported by the following institution and Agencies: the Italian Space Agency (ASI, Italy) (grant ASI I/004/12/2), the National Aeronautics and Space Administration (NASA, USA) and Deutsches Zentrum für Luft- und Raumfahrt (DLR, Germany).
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Michael Sori and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Pan-sharpened FC colour data showing an asymmetric distribution of reddish material (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA).
Pasola Facula. Left) mosaic of Pasola facula located on the western side of Cerealia Facula (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA); Right): Map of Pasola Facula showing VIR coverage (in grey) along with the main geologic features. Units label are: bd, the bright discontinuous unit – bc, bright continuous unit and t, talus material.
An example of spectra of Cerealia facula with highlighted the main features within the 2.6–3.5 micron band.
Average spectrum of the pixels covering the southern part of Pasola Facula. The data at 2.5 micron has been removed because affected by the detector filters.
The spectrum used for the spectral modelling is an average of the spectra of the pixels on the bright Cerealia facula selected on the basis of the absolute reflectance (median reflectance > 5 times median reflectance of dark surrounding regions, in the range 2.6 – 3.4 µm). Dataset used is described in Extended Data Table 4. A) spectral fit using the species reported in Extended Data Table 3, without organics; B) spectral fit using the species reported in Extended Data Table 3, including low-anthraxolite; C) spectral fit using the species reported in Extended Data Table 3, including IOM. The data 2.5 micron has been removed because affected by the detector filters.
a) Temperature of the hydrohalite rich region, located at the centre of Occator, at different heliocentric distances: aphelium, perihelium and 2.70 AU; B) Dehydration rate on Occator at same heliocentric distances; C) 3-D reconstruction of Occator used in our numerical modelling.
Species used in the spectral fits, retrieved abundance and X2 of the spectral modelling. The percentage are expressed in cross section (% of surface). The end member spectra are taken form RELAB except for Sol.3 from 22. The spectrum used for the fits is the average of the spectra of samples 61-64, line 82, scet 582998159.
Species present in frozen ammonium-sodium-chloride-carbonate brine mixtures from ref. 22. Solution 1 was prepared with an equal amount of sodium and ammonium ions. Solution 2 was prepared at room temperature and was composed of 0.6 M [Na+], 3.6 M [NH4+], 3.6 M [Cl−], and 0.3 M [CO3 2−]. Solution 3 was prepared at room temperature and composed of 3.1 M [Na+], 0.6 M [NH4+], 3.1 M [Cl−], and 0.3 M [CO32−]. See ref. 22 for details.
Species used in the spectral fits, retrieved abundance and Χ2 of the spectral modelling. The spectrum used for the spectral modelling is an average of the spectra of the pixels on the bright Cerealia facula selected on the basis of the absolute reflectance (median reflectance > 5 times median reflectance of dark surrounding regions, in the range 2.6 – 3.4 µm). The percentage are expressed in cross section (% of surface). Dataset used is described in Extended Data Fig. 10.
VIR infrared data used in this analysis.
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De Sanctis, M.C., Ammannito, E., Raponi, A. et al. Fresh emplacement of hydrated sodium chloride on Ceres from ascending salty fluids. Nat Astron 4, 786–793 (2020). https://doi.org/10.1038/s41550-020-1138-8
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