Evidence of non-uniform crust of Ceres from Dawn’s high-resolution gravity data

Abstract

The gravity and shape data acquired by the Dawn spacecraft during its primary mission revealed that Ceres is partially differentiated with an interior structure consistent with a volatile-rich crust, a mantle of hydrated rock and isostatically compensated topography1,2,3. Detailed analyses showed that the mechanically strong crust overlays a weak, fluid-bearing upper mantle4. Previous studies, however, assumed that Ceres’s crust is a uniform layer. Here, we report findings from the new high-resolution gravity data from Dawn’s second extended mission (XM2), which reveal a complex crustal structure of Ceres. In the low-altitude regions probed by the Dawn spacecraft during the XM2 phase, we observe that gravity–topography admittance progressively shifts to a lower density solution at higher degrees, implying a radial density gradient across Ceres’s crust that is consistent with decreasing porosity with depth and/or increasing content of dense phases, such as rock and salts. That gradient brings a critical new constraint on the crustal freezing history, suggesting that the salts and silicates concentrated in the liquid phase while the crust was growing. Localized spectral analysis of the new data also shows evidence for a lower crustal density in the north polar region than in the south or near the equator, supporting impact-driven porosity variations for the observed latitudinal density differences5. On the local scale, the new data show evidence for density or rheological variations within the crust, in association with lobate landslides and ejecta deposits that were inferred to be ice-rich6,7 as well as an extensional fault system8. These inferences provide geophysical context for geological features on the surface and help us advance our understanding of the evolution of an ice-rich but heat-starved body, whose evolution was in part shaped by impacts.

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Fig. 1: Maps of DS, isostatic anomaly and height above geoid.
Fig. 2: Global and localized admittance and correlation.
Fig. 3: Local admittance analysis.
Fig. 4: Maps of isostatic anomaly for several regions of interest computed from degree 3 to local DS.

Data availability

The data that support the plots within this paper and other findings of this study are available from the PDS Small Bodies Node website (https://sbn.psi.edu/pds/resource/dawn) or from the corresponding author on reasonable request.

Code availability

We have opted not to make the code available because it is based on well-known theories for orbit and shape determinations, as described in Methods.

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Acknowledgements

This research was in part carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We thank the Dawn operations team for the development, cruise, orbital insertion and operations of the Dawn spacecraft at Ceres. Government sponsorship acknowledged. All rights reserved.

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Contributions

R.S.P, A.S.K. and A.T.V. performed data analysis and calibration. R.S.P, A.I.E., J.C.C.-R., R.R.F., K.H.G.H., T.H.P., C.A.R., J.E.C.S., H.G.S., M.M.S., G.M., B.E.S. and C.T.R. contributed to the interpretation of the data. All authors contributed to the discussion of the results and to writing the paper.

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Correspondence to R. S. Park.

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Supplementary Figs. 1–10 and Tables 1 and 2.

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Park, R.S., Konopliv, A.S., Ermakov, A.I. et al. Evidence of non-uniform crust of Ceres from Dawn’s high-resolution gravity data. Nat Astron 4, 748–755 (2020). https://doi.org/10.1038/s41550-020-1019-1

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