NASA's Dawn spacecraft has observed terrains rich in dark material on the surface of Vesta. Spectral data suggest that these terrains share a similar composition with the class of meteorites known as carbonaceous chondrites, suggesting that the dark material could have been delivered by meteorite impacts.
Vishnu Reddy at the Max Plank Institute for Solar System Research, Germany, and colleagues analysed Dawn images to characterize the properties of the low-albedo dark material. They find that the majority of dark terrains are composed of similar materials, and that dark material is particularly abundant around the rim of the ancient south polar crater Veneneia. This is consistent with an origin of the dark material from impacts rather than volcanism. They suggest that Veneneia is the product of a collision with a carbonaceous chondrite, which deposited a mixture of dark material and surface rocks as ejecta around the resulting crater. Smaller impacts of carbon-rich asteroids could explain the distribution of dark material elsewhere on Vesta's surface.
Intriguingly, the similarities between the dark material and carbonaceous clasts in howardite meteorites found on Earth are further evidence that these meteorites originally hailed from Vesta.
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Goldin, T. Vesta's veneer. Nature Geosci 5, 762 (2012). https://doi.org/10.1038/ngeo1630
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DOI: https://doi.org/10.1038/ngeo1630
