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Dark material on Vesta from the infall of carbonaceous volatile-rich material

Abstract

Localized dark and bright materials, often with extremely different albedos, were recently found on Vesta’s surface1,2. The range of albedos is among the largest observed on Solar System rocky bodies. These dark materials, often associated with craters, appear in ejecta and crater walls, and their pyroxene absorption strengths are correlated with material brightness. It was tentatively suggested that the dark material on Vesta could be either exogenic, from carbon-rich, low-velocity impactors, or endogenic, from freshly exposed mafic material or impact melt, created or exposed by impacts. Here we report Vesta spectra and images and use them to derive and interpret the properties of the ‘pure’ dark and bright materials. We argue that the dark material is mainly from infall of hydrated carbonaceous material (like that found in a major class of meteorites and some comet surfaces3,4,5), whereas the bright material is the uncontaminated indigenous Vesta basaltic soil. Dark material from low-albedo impactors is diffused over time through the Vestan regolith by impact mixing, creating broader, diffuse darker regions and finally Vesta’s background surface material. This is consistent with howardite–eucrite–diogenite meteorites coming from Vesta.

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Figure 1: Locations of dark and bright material.
Figure 2: Frequency distribution of albedos.
Figure 3: Reflectance spectra of dark and bright materials.
Figure 4: Correlation of pyroxene absorption with material reflectance.
Figure 5: Correlation of OH spectral absorption with material reflectance.

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Acknowledgements

This research was supported by the NASA Dawn Project under contract from UCLA, by the NASA Dawn at Vesta Participating Scientist program, the Italian Space Agency, the Max Planck Institute for Solar System Research, and the Germany Aerospace Agency (DLR). We acknowledge the support of the Dawn Science, Instrument and Operations Teams.

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T.B.McC. designed the study, directed the research and wrote the manuscript; J.-P.C., J-Y.L. and H.Y.McS. were the major contributors helping to design the study, direct the research and write the manuscript. D.T., T.B.McC. and J.-P.C. wrote the Supplementary Information. J.-P.C. performed the spectral unmixing of the VIR mapping spectrometer data and the correlation of OH with albedo. J.-P.C. and F.T. produced global maps from the VIR mapping spectrometer data. V.R. performed the correlation of albedo with band strength. L.L.C. and R.J. produced global mapping of Vesta with Framing Camera images. H.Y.McS., V.R. and D.W.M. contributed to the laboratory analysis of Vestan meteorites. J.-P.C., E.P., E.A., M.C.D.S. and A.L. contributed to the location of dark materials and to the spectral analysis of hydroxyl-rich areas from the VIR mapping spectrometer data. R.J. provided the location of dark materials from Framing Camera images. D.T. provided estimates of amounts of dark material coming from carbonaceous chondrite meteorites. J.-P.C., J-Y.L., F.C., E.P. and A.L. contributed to the photometric correction for the VIR mapping spectrometer. J-Y.L., S.E.S. and L.L.C. contributed to the photometric correction of Framing Camera images. F.T. and J.-P.C. investigated the need for thermal emission correction of the VIR mapping spectrometer. D.A.W. contributed much of the geologic context of dark material, developed example site descriptions, and wrote or edited geological context materials. D.T.B. participated in developing the dark-material interpretation and edited the manuscript. C.M.P. participated in providing context for the mixing effects on the resulting surface material and integrating space-weathering concepts. M.C.D.S. is the Principal Investigator of the VIR mapping spectrometer and helped to provide the VIR data. A.N. is the Principal Investigator of the Framing Camera and helped to provide the Framing Camera data. M.T.C. and F.C. analysed the thermal properties of the surface of Vesta. D.W.M. located bright materials from Framing Camera images. E.A., F.C., F.T., A.L., M.C.D.S. and J.-P.C. contributed to the calibration of the VIR mapping spectrometer. A.N., S.E.S. and V.R. contributed to the calibration of the Framing Camera. E.A. contributed to the sequencing of data acquisition for the VIR mapping spectrometer. S.E.S. contributed to the sequencing of data acquisition for the Framing Camera. H.H. contributed to the design and development of the Framing Camera. A.W.B., U.C., H.U.K., B.W.D. & J.M.S. participated in the working group studying the bright material. C.A.R. is the deputy Principal Investigator of the Dawn mission. C.T.R. is the Principal Investigator of the Dawn mission. All authors discussed the results and commented on the manuscript.

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Correspondence to T. B. McCord or J.-P. Combe.

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The authors declare no competing financial interests.

Additional information

Data from the Dawn mission are publicly available through the NASA Planetary Data System.

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Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figure 1 and additional references. (PDF 246 kb)

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McCord, T., Li, JY., Combe, JP. et al. Dark material on Vesta from the infall of carbonaceous volatile-rich material. Nature 491, 83–86 (2012). https://doi.org/10.1038/nature11561

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