Is Vesta an intact and pristine protoplanet?

•No chondritic composition model fits the Dawn data for Vesta’s density, core size, lack of exposed mantle material.•Vesta’s core is consistent with that of an H chondrite composition, but the density of a sodium-depleted H mineralogy is much higher than that of Vesta, requiring significant macropor...

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Bibliographic Details
Published in:Icarus (New York, N.Y. 1962) N.Y. 1962), 2015-07, Vol.254, p.190-201
Main Authors: Consolmagno, G.J., Golabek, G.J., Turrini, D., Jutzi, M., Sirono, S., Svetsov, V., Tsiganis, K.
Format: Article
Language:English
Subjects:
Asteroid Vesta
Asteroids
Asteroids, composition
Density
Enrichment
Formations
Mantle
Meteorites
Planetary formation
Sodium
Vesta asteroid
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Summary:•No chondritic composition model fits the Dawn data for Vesta’s density, core size, lack of exposed mantle material.•Vesta’s core is consistent with that of an H chondrite composition, but the density of a sodium-depleted H mineralogy is much higher than that of Vesta, requiring significant macroporosity deep into the crust or mantle – difficult to reconcile with Vesta’s history of differentiation.•Even with a thick orthopyroxene upper mantle and/or unusually dense lower mantle, to match Vesta’s bulk density and large core requires a crust too thin to hide the olivine mantle from exposure during the formation of the large south pole basins.•We suggest that Vesta has been radically altered since the period when the HED meteorites were formed. It is difficult to find a Vesta model of iron core, pyroxene and olivine-rich mantle, and HED crust that can match the joint constraints of (a) Vesta’s density and core size as reported by the Dawn spacecraft team; (b) the chemical trends of the HED meteorites, including the depletion of sodium, the FeO abundance, and the trace element enrichments; and (c) the absence of exposed mantle material on Vesta’s surface, among Vestoid asteroids, or in our collection of basaltic meteorites. These conclusions are based entirely on mass-balance and density arguments, independent of any particular formation scenario for the HED meteorites themselves. We suggest that Vesta either formed from source material with non-chondritic composition or underwent after its formation a radical physical alteration, possibly caused by collisional processes, that affected its global composition and interior structure.
ISSN:0019-1035
1090-2643
DOI:10.1016/j.icarus.2015.03.029