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Fresh emplacement of hydrated sodium chloride on Ceres from ascending salty fluids

Abstract

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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Fig. 1: Cerealia Facula.
Fig. 2: Morphology and colours of Cerealia Tholus.
Fig. 3: Band intensity.
Fig. 4: Cerealia spectral ratio compared with laboratory spectra of brines.
Fig. 5: Spectral fits of the pixels in area A using different mixtures.
Fig. 6: Brines on Cerealia Facula.

Data availability

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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Acknowledgements

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).

Author information

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Authors

Contributions

M.C.D.S. elaborated interpreted VIR data, and wrote most of the manuscript. A.F. elaborated the VIR data projections over FC data. A.R. developed the spectral modelling of the spectra. M. Formisano developed the thermal model. All authors participated in data acquisition, discussion of results and/or editing of the manuscript.

Corresponding author

Correspondence to M. C. De Sanctis.

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Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Michael Sori and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Cerealia Facula.

Pan-sharpened FC colour data showing an asymmetric distribution of reddish material (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA).

Extended Data Fig. 2 Pasola Facula.

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.

Extended Data Fig. 3 A typical spectrum of Cerealia facula.

An example of spectra of Cerealia facula with highlighted the main features within the 2.6–3.5 micron band.

Extended Data Fig. 4 Spectrum of the southern part of Pasola Facula.

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.

Extended Data Fig. 5 Spectral fits of the average spectrum of Cerealia facula.

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.

Extended Data Fig. 6 Thermal models of the hydrohalite rich area.

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.

Extended Data Fig. 7 Spectral 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.

Extended Data Fig. 8 Species present in frozen ammonium-sodium-chloride-carbonate brine mixtures.

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.

Extended Data Fig. 9 Spectral modelling of the brightest pixels, including organic species.

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.

Extended Data Fig. 10 VIR data used in the spectral modelling.

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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